feat: buffered decoding API

.gitignore

@@ -1,7 +1,4 @@
+.vscode/
 ols.json
 odinfmt.json
-example/
+tests/*.flac
-example/!*.odin
-tests/test-files/LPC_example.flac
-tests/test-files/fixed_example.flac
-tests/test-files/verbatim_example.flac

TODO.md

@@ -2,11 +2,14 @@ Files:-
 27 -> This one uses the old format of specifying a variable block strategy. Look into it.
 	  The way to know the blocking strategy for this old format FLACs is to see if min_block_size and max_block_size are different,
 	  if they are, then the blocking strategy is VARIABLE, if not, then it's FIXED.
-44 -> High memory and CPU usage. needs optimization.
 
-uncommon/01 -> This one decodes fine but the expected MD5 is 0x00 * 16 which doesn't match the calculated MD5. not sure what to do about this.
+Playback issues in the example program that may relate to the decoder:-
-uncommon/02 -> No MD5
+05 - CRC fails for a frame. The gotten CRC is different each time, expected CRC is also different sometimes.
-uncommon/03 -> No MD5
+06 - Same as above
+23 - Crunchy loud noise mixed with the actual audio data
+25 - Same CRC problem
+It's worth noting that if we get rid of the CRC checks the files play just fine.
+
 uncommon/04 -> We get a bits per sample mismatch
 uncommon/10 -> We error with Invalid Signature. I assume for these two I should look for the frame sync bits. But maybe my decoder should reject these. idk.
 uncommon/11 -> We error with Invalid Signature
@@ -14,19 +17,24 @@ uncommon/11 -> We error with Invalid Signature
 faulty/01 -> This one works when it shouldn't (Wrong max blocksize)
 faulty/02 -> This one works when it shouldn't (Wrong max framesize)
 faulty/04 -> This one works when it shouldn't. This one has a wrong number of channels (whatever that means)
+			 Each frame has to be played by itself, otherwise plays sped up.
 faulty/05 -> This one works when it shouldn't. (Wrong number of samples)
+			 This should be fine to decode and play.
 faulty/08 -> This one works when it shouldn't. (Blocksize 65536, exceeds the allowed max of 65535)
-faulty/09 -> This one works when it shouldn't. (Blocksize 1, below the allowed min of 16 (last frame(subframe?) is allowed to have less than 16))
+			 We should error here. We segfault currently.
+faulty/09 -> This one works when it shouldn't. (Blocksize 1, below the allowed min of 16 (only the last frame is allowed to have less than 16))
+			 We should error here. We play correctly currently.
+faulty/11 -> We return an error now, but we should just warn and decode the audio fine.
 
 Things:-
 [ ] Options
-	- [ ] Vorbis comment data
+	- [x] Vorbis comment data
 	- [ ] Cuesheet ?
 	- [ ] Seektable ?
 	- [x] Picture data
-[ ] File streaming API? io.Stream??
+[x] File streaming API? io.Stream??
 [ ] Lots of checks (look at the TODOs in flac.odin)
-[ ] Memory optimizations
+[x] Memory optimizations
 [ ] Speed optimizations
 [ ] Seeking
 [ ] Fuzzing to test the stability of the code

example/main.odin

@@ -1,36 +0,0 @@
-package flac_example
-
-import "core:fmt"
-import "core:mem"
-import "core:mem/virtual"
-import "core:os"
-import "core:time"
-
-import "../"
-
-main :: proc() {
-    if len(os.args) < 2 {
-        fmt.eprintln("Please provide a path to a flac file.")
-        os.exit(1)
-    }
-
-    arena: virtual.Arena
-    arena_err := virtual.arena_init_static(&arena, mem.Megabyte * 8)
-    if arena_err != nil {
-        fmt.eprintln("Failed to alloc memory")
-        return
-    }
-    allocator := virtual.arena_allocator(&arena)
-
-    start := time.now()
-    flac_data, err := flac.load_from_file(os.args[1], allocator = allocator)
-    if err != nil {
-        fmt.eprintln(err)
-        os.exit(1)
-    }
-
-    end := time.now()
-
-    elapsed := time.diff(start, end)
-    fmt.println("Decoding took", elapsed)
-}

examples/buffered/main.odin

@@ -0,0 +1,189 @@
+package flac_example
+
+import "core:fmt"
+import "core:mem"
+import "core:mem/virtual"
+import "core:crypto/legacy/md5"
+import "core:os"
+import "core:time"
+
+import "shared:flac"
+import "shared:alsa"
+
+DEVICE :: "default"
+
+main :: proc() {
+    if len(os.args) < 2 {
+        fmt.eprintln("Please provide a path to a flac file.")
+        os.exit(1)
+    }
+
+    arena: virtual.Arena
+    handle: ^alsa.pcm_t
+
+    alsa_err := alsa.pcm_open(&handle, DEVICE, .PLAYBACK, .BLOCK)
+    if alsa_err < 0 {
+        fmt.eprintln("Failed to initialize audio device: ", alsa.strerror(alsa_err))
+        os.exit(1)
+    }
+
+    arena_err := virtual.arena_init_growing(&arena, mem.Megabyte * 8)
+    if arena_err != nil {
+        fmt.eprintln("Failed to alloc memory")
+        return
+    }
+    allocator := virtual.arena_allocator(&arena)
+
+    start := time.now()
+    flac_data, reader, err := flac.load_from_file_buffered(os.args[1], allocator)
+    if err != nil {
+        fmt.println("Error while reading flac file:", err)
+        os.exit(1)
+    }
+    defer flac.destroy(flac_data, reader, allocator)
+
+    fmt.println(flac_data)
+
+	alsa_err = alsa.pcm_set_params(handle, .S16_LE, .RW_INTERLEAVED, u32(flac_data.metadata.channels), flac_data.metadata.sample_rate, 1, 500000)
+	if alsa_err < 0 {
+		fmt.eprintln("Playback open error:", alsa.strerror(alsa_err))
+		os.exit(1)
+	}
+
+	sample_rate := flac_data.metadata.sample_rate
+	channels := flac_data.metadata.channels
+
+    //md5_ctx: md5.Context
+    //md5.init(&md5_ctx)
+    for {
+        frame, err := flac.read_next_frame(reader, flac_data)
+
+        defer delete(frame.samples)
+        if err != nil {
+            if err == .EOF {
+                break
+            } else {
+                fmt.println("Error while decoding frame:", err)
+                os.exit(1)
+            }
+        }
+
+		//if frame.sample_rate != sample_rate || frame.channels != channels {
+		//	sample_rate = frame.sample_rate
+		//	channels = frame.channels
+		//	alsa_err = alsa.pcm_set_params(handle, .S16_LE, .RW_INTERLEAVED, u32(channels), sample_rate, 1, 0)
+		//	if alsa_err < 0 {
+		//		fmt.eprintln("Playback open error:", alsa.strerror(alsa_err))
+		//		os.exit(1)
+		//	}
+		//}
+
+        //converted_samples := make([]u8, len(samples))
+        //defer delete(converted_samples)
+        //for sample, i in samples {
+        //    converted_samples[i] = u8(sample & 0xFF)
+        //}
+
+        converted_samples := make([]i16, len(frame.samples))
+        defer delete(converted_samples)
+        for sample, i in frame.samples {
+            new_sample := sample & 0xFF
+            new_sample |= ((sample >> 8) & 0xFF) << 8
+            converted_samples[i] = i16(new_sample)
+        }
+
+        frames := alsa.pcm_writei(handle, raw_data(converted_samples), u64(len(frame.samples)) / u64(frame.channels))
+        if frames < 0 {
+            fmt.eprintln("Error writing to PCM device:", alsa.strerror(auto_cast frames))
+            break
+        }
+        fmt.printfln("Played %d frames", frames)
+
+        //flac.md5hash(&md5_ctx, flac_data.metadata.bits_per_sample, samples)
+    }
+    end := time.now()
+
+    //err = flac.md5sum(&md5_ctx, flac_data)
+    //if err == .MD5_Mismatch {
+    //    fmt.println("Decoded audio data is not correct.")
+    //    os.exit(1)
+    //}
+
+    alsa_err = alsa.pcm_drain(handle)
+    if alsa_err < 0 {
+        fmt.eprintln("pcm_drain failed with:", alsa.strerror(alsa_err))
+    }
+    alsa.pcm_close(handle)
+
+    elapsed := time.diff(start, end)
+    fmt.println("Decoding took", elapsed)
+}
+
+old_main :: proc() {
+    if len(os.args) < 2 {
+        fmt.eprintln("Please provide a path to a flac file.")
+        os.exit(1)
+    }
+
+    handle: ^alsa.pcm_t
+
+    arena: virtual.Arena
+    arena_err := virtual.arena_init_growing(&arena, mem.Megabyte * 8)
+    if arena_err != nil {
+        fmt.eprintln("Failed to alloc memory")
+        return
+    }
+    allocator := virtual.arena_allocator(&arena)
+
+    alsa_err := alsa.pcm_open(&handle, DEVICE, .PLAYBACK, .BLOCK)
+    if alsa_err < 0 {
+        fmt.eprintln("Failed to initialize audio device: ", alsa.strerror(alsa_err))
+        os.exit(1)
+    }
+
+    start := time.now()
+    flac_data, err := flac.load_from_file(os.args[1], allocator = allocator)
+    if err != nil {
+        fmt.eprintln(err)
+        if err == .MD5_Mismatch {
+            fmt.printfln("Expected: %v, got: %v", flac_data.metadata.expected_md5, flac_data.metadata.calculated_md5)
+        }
+        os.exit(1)
+    }
+    defer flac.destroy(flac_data, allocator = allocator)
+    end := time.now()
+
+    fmt.println(flac_data.metadata)
+
+    alsa_err = alsa.pcm_set_params(handle, .S16_LE, .RW_INTERLEAVED, u32(flac_data.metadata.channels), flac_data.metadata.sample_rate, 1, 500000)
+    if alsa_err < 0 {
+        fmt.eprintln("Playback open error:", alsa.strerror(alsa_err))
+        os.exit(1)
+    }
+
+    converted_samples := make([]i16, len(flac_data.samples))
+
+    for sample, i in flac_data.samples {
+        new_sample := sample & 0xFF
+        new_sample |= ((sample >> 8) & 0xFF) << 8
+        converted_samples[i] = i16(new_sample)
+    }
+
+    for {
+        frames := alsa.pcm_writei(handle, raw_data(converted_samples), u64(len(flac_data.samples)) / u64(flac_data.metadata.channels))
+        if frames < 0 {
+            fmt.eprintln("Error writing to PCM device:", alsa.strerror(auto_cast frames))
+            break
+        }
+        fmt.printfln("Played %d frames", frames)
+    }
+
+    alsa_err = alsa.pcm_drain(handle)
+    if alsa_err < 0 {
+        fmt.eprintln("pcm_drain failed with:", alsa.strerror(alsa_err))
+    }
+    alsa.pcm_close(handle)
+
+    elapsed := time.diff(start, end)
+    fmt.println("Decoding took", elapsed)
+}

examples/in_memory/main.odin

@@ -0,0 +1,81 @@
+package main
+
+import "core:os"
+import "core:fmt"
+import "core:mem"
+import "core:mem/virtual"
+import "core:time"
+
+import "shared:alsa"
+import "shared:flac"
+
+DEVICE :: "default"
+
+main :: proc() {
+    if len(os.args) < 2 {
+        fmt.eprintln("Please provide a path to a flac file.")
+        os.exit(1)
+    }
+
+    handle: ^alsa.pcm_t
+
+    arena: virtual.Arena
+    arena_err := virtual.arena_init_growing(&arena, mem.Megabyte * 8)
+    if arena_err != nil {
+        fmt.eprintln("Failed to alloc memory")
+        return
+    }
+    allocator := virtual.arena_allocator(&arena)
+
+    alsa_err := alsa.pcm_open(&handle, DEVICE, .PLAYBACK, .BLOCK)
+    if alsa_err < 0 {
+        fmt.eprintln("Failed to initialize audio device: ", alsa.strerror(alsa_err))
+        os.exit(1)
+    }
+
+    start := time.now()
+    flac_data, err := flac.load_from_file(os.args[1], allocator = allocator)
+    if err != nil {
+        fmt.eprintln(err)
+        if err == .MD5_Mismatch {
+            fmt.printfln("Expected: %v, got: %v", flac_data.metadata.expected_md5, flac_data.metadata.calculated_md5)
+        }
+        os.exit(1)
+    }
+    defer flac.destroy(flac_data, allocator = allocator)
+    end := time.now()
+
+    fmt.println(flac_data.metadata)
+
+    alsa_err = alsa.pcm_set_params(handle, .S16_LE, .RW_INTERLEAVED, u32(flac_data.metadata.channels), flac_data.metadata.sample_rate, 1, 500000)
+    if alsa_err < 0 {
+        fmt.eprintln("Playback open error:", alsa.strerror(alsa_err))
+        os.exit(1)
+    }
+
+    converted_samples := make([]i16, len(flac_data.samples))
+
+    for sample, i in flac_data.samples {
+        new_sample := sample & 0xFF
+        new_sample |= ((sample >> 8) & 0xFF) << 8
+        converted_samples[i] = i16(new_sample)
+    }
+
+    for {
+        frames := alsa.pcm_writei(handle, raw_data(converted_samples), u64(len(flac_data.samples)) / u64(flac_data.metadata.channels))
+        if frames < 0 {
+            fmt.eprintln("Error writing to PCM device:", alsa.strerror(auto_cast frames))
+            break
+        }
+        fmt.printfln("Played %d frames", frames)
+    }
+
+    alsa_err = alsa.pcm_drain(handle)
+    if alsa_err < 0 {
+        fmt.eprintln("pcm_drain failed with:", alsa.strerror(alsa_err))
+    }
+    alsa.pcm_close(handle)
+
+    elapsed := time.diff(start, end)
+    fmt.println("Decoding took", elapsed)
+}

flac.odin

@@ -1,6 +1,7 @@
 package flac
 
 import "core:bytes"
+import "core:bufio"
 import "core:crypto/legacy/md5"
 import "core:fmt"
 import "core:io"
@@ -20,7 +21,6 @@ FlacError :: enum {
     Missing_StreamInfo,
     Missing_Lead_Out_Track,
     Invalid_Coefficient_Precision,
-    Metadata_Block_Length_Mismatch,
     CRC_Mismatch,
     MD5_Mismatch,
     Unsupported_BPS, // Remove when implemented
@@ -36,17 +36,12 @@ Option:
     `.skip_md5_check`
         Skips checking the MD5 hash of the decoded sample data.
         Offers a slight performance increase but will not error if the data is incorrect.
-    `.only_return_picture_data`
-        Returns the embedded picture metadata and encoded pixel data (if available)
-        `.only_return_metadata` includes this.
     `.only_return_metadata`
         Returns all metadata of a FLAC stream without decoding the audio data.
 */
 
-// TODO: Implement these
 Option :: enum {
     skip_md5_check,
-    only_return_picture_data,
     only_return_metadata,
 }
 
@@ -77,9 +72,8 @@ PictureType :: enum u32 {
 }
 
 Flac :: struct {
-    // TODO: Other stuff
     metadata: FlacMetadata,
-    samples:  []i32,
+    samples:  [dynamic]i32,
 }
 
 FlacMetadata :: struct {
@@ -90,6 +84,8 @@ FlacMetadata :: struct {
     expected_md5:    [16]byte,
     calculated_md5:  [16]byte,
     pictures:        []Picture,
+    vendor_name:     string,
+    vorbis_comments: []string,
 }
 
 Picture :: struct {
@@ -103,14 +99,17 @@ Picture :: struct {
     data: []byte,
 }
 
+Frame :: struct {
+    channels: u8,
+    sample_rate: u32,
+    samples: []i32,
+}
+
+@(private)
 decode_subframe :: proc(r: ^Reader, bps: u8, block_size: u16) -> (samples: []i32, err: Error) #no_bounds_check {
-    // TODO: temp allocator?? so we copy the slice of data into the _actual_ sample buffer
-    // Maybe even a static arena with a size of 32MB by default (and configurable using #config) or something
-    // that we then use to allocate from (better perf is the reason because allocating on the heap for every subframe
-    // is probably noticibly slower)
     subframe_samples := make([]i32, block_size)
 
-    data := read_byte(r) or_return
+    data := read_bits(r, 8) or_return
 
     subframe_type := (data & 0x7E) >> 1
     low_3_bits := subframe_type & 7
@@ -118,7 +117,7 @@ decode_subframe :: proc(r: ^Reader, bps: u8, block_size: u16) -> (samples: []i32
     wasted_bits := 0
 
     if has_wasted_bits {
-        for (read_bit(r) or_return) != 1 {
+        for (read_bits(r, 1) or_return) != 1 {
             wasted_bits += 1
         }
         wasted_bits += 1
@@ -251,7 +250,7 @@ decode_subframe :: proc(r: ^Reader, bps: u8, block_size: u16) -> (samples: []i32
                 for s in 0..<num_samples {
                     quotient := 0
                     // Read bits until we encounter a 1 (also called unary encoding). That's our quotient.
-                    for (read_bit(r) or_return) != 1 {
+                    for (read_bits(r, 1) or_return) != 1 {
                         quotient += 1
                     }
                     remainder := int(read_bits(r, uint(rice_parameter)) or_return)
@@ -352,7 +351,7 @@ decode_subframe :: proc(r: ^Reader, bps: u8, block_size: u16) -> (samples: []i32
                 for s in 0..<num_samples {
                     quotient := 0
                     // Read bits until we encounter a 1 (also called unary encoding). That's our quotient.
-                    for (read_bit(r) or_return) != 1 {
+                    for (read_bits(r, 1) or_return) != 1 {
                         quotient += 1
                     }
                     remainder := int(read_bits(r, uint(rice_parameter)) or_return)
@@ -395,22 +394,29 @@ decode_subframe :: proc(r: ^Reader, bps: u8, block_size: u16) -> (samples: []i32
     return subframe_samples, nil
 }
 
-// TODO: remove
+@(private)
-frame_num := 0
-
 decode_frame :: proc(
     r: ^Reader,
     flac: ^Flac,
+    md5_ctx: ^md5.Context,
+    options: Options,
 ) -> (
     err: Error,
 ) #no_bounds_check {
     //
     // Frame Header
     //
-    frame_beginning := r.i
+    tee_r: io.Tee_Reader
-
+    crc_buffer: bytes.Buffer
-    //fmt.println("STARTING FRAME", frame_num)
+    bytes.buffer_init_allocator(&crc_buffer, 0, 128)
-    //fmt.println("FRAME START AT OFFSET:", r.i)
+    defer bytes.buffer_destroy(&crc_buffer)
+    crc := bytes.buffer_to_stream(&crc_buffer)
+    r := &Reader{
+        r = io.tee_reader_init(&tee_r, r, crc),
+        buf = r.buf,
+        x = r.x,
+        n = r.n,
+    }
 
     data := read_data(r, u16be) or_return
 
@@ -451,7 +457,7 @@ decode_frame :: proc(
         case 2..=5:
             actual_block_size = 576 * auto_cast (pow2(block_size - 2))
         case 6:
-            actual_block_size = auto_cast (read_byte(r) or_return) + 1
+            actual_block_size = auto_cast (read_bits(r, 8) or_return) + 1
         case 7:
             actual_block_size = (read_data(r, u16be) or_return) + 1
         case 8..=15:
@@ -491,7 +497,7 @@ decode_frame :: proc(
         case ._96kHz:
             actual_sample_rate_in_Hz = 96000
         case .USE_8_BITS_IN_kHz_FROM_HEADER_END:
-            actual_sample_rate_in_Hz = auto_cast (read_byte(r) or_return) * 1000
+            actual_sample_rate_in_Hz = auto_cast (read_bits(r, 8) or_return) * 1000
         case .USE_16_BITS_IN_Hz_FROM_HEADER_END:
             actual_sample_rate_in_Hz = auto_cast (read_data(r, u16be) or_return)
         case .USE_16_BITS_IN_TENS_OF_Hz_FROM_HEADER_END:
@@ -504,16 +510,9 @@ decode_frame :: proc(
     // TODO: sample rate MUST NOT be 0 if the subframe contains audio.
     // a sample rate of 0 MAY be used when non-audio is represented.
 
-    frame_header_end := r.i
+    crc8_bytes := bytes.buffer_to_bytes(&crc_buffer)
-
+    frame_header_crc := u8(read_bits(r, 8) or_return)
-    frame_header_crc := read_byte(r) or_return
+    calculated_header_crc := calculate_crc8(crc8_bytes)
-    calculated_header_crc := calculate_crc8(r.s[frame_beginning:frame_header_end])
-
-    //fmt.printfln("block size bits: 0b%b", block_size)
-    //fmt.printfln("actual block size: %d sample(s)", actual_block_size)
-    //fmt.println("sample rate bits:", sample_rate)
-    //fmt.printfln("actual sample rate: %dHz", actual_sample_rate_in_Hz)
-    //fmt.println("channel assignment:", channel_assignment)
 
     if frame_header_crc != calculated_header_crc {
         fmt.printfln("Expected frame header CRC: 0x%X, got: 0x%X", frame_header_crc, calculated_header_crc)
@@ -576,7 +575,6 @@ decode_frame :: proc(
         // so many questions...
     }
 
-    // TODO: remember to clean this up
     subframes := make([][]i32, frame_channels)
     defer delete(subframes)
     for i in 0..<frame_channels {
@@ -594,6 +592,59 @@ decode_frame :: proc(
 
     align_to_byte(r)
 
+    correlate(subframes, channel_assignment)
+
+    // Write the samples interleaved.
+    for i in 0..<len(subframes[0]) {
+        for subframe, sf in subframes {
+            sample := subframe[i]
+            append(&flac.samples, sample)
+
+            if .skip_md5_check not_in options {
+                switch bps {
+                    case 1..=8:
+                        md5.update(md5_ctx, {u8(sample)})
+                    case 9..=16:
+                        first_byte := u8(sample & 0xFF)
+                        second_byte := u8((sample >> 8) & 0xFF)
+                        md5.update(md5_ctx, {first_byte, second_byte})
+                    case 17..=24:
+                        first_byte := u8(sample & 0xFF)
+                        second_byte := u8((sample >> 8) & 0xFF)
+                        third_byte := u8((sample >> 16) & 0xFF)
+                        md5.update(md5_ctx, {first_byte, second_byte, third_byte})
+                    case 25..=32:
+                        data := transmute([4]u8)sample
+                        md5.update(md5_ctx, data[:])
+                    case:
+                        fmt.println("INVALID BPS")
+                        os.exit(1)
+                }
+            }
+        }
+    }
+
+    for subframe in subframes {
+        delete(subframe)
+    }
+
+    //
+    // Frame Footer
+    //
+    crc16_bytes := bytes.buffer_to_bytes(&crc_buffer)
+    frame_crc := u16(read_data(r, u16be) or_return)
+    calculated_frame_crc := calculate_crc16(crc16_bytes)
+
+    if frame_crc != calculated_frame_crc {
+        fmt.eprintfln("Expected frame CRC 0x%X, got 0x%X", frame_crc, calculated_frame_crc)
+        return .CRC_Mismatch
+    }
+
+    return nil
+}
+
+@(private)
+correlate :: proc(subframes: [][]i32, channel_assignment: ChannelAssignment) {
     // Undo Stereo Decorrelation
     #partial switch channel_assignment {
         case .STEREO_MID_SIDE:
@@ -625,67 +676,11 @@ decode_frame :: proc(
                 subframes[1][i] = left - side
             }
     }
-
-    // TODO: Maybe this is slow if we have a lot of samples??
-    // The cases are ranges because streaminfo can define unusual bits per sample
-    for i in 0..<len(subframes[0]) {
-        for subframe in subframes {
-            sample := subframe[i]
-            switch bps {
-                case 1..=8:
-                    md5.update(&md5_ctx, {u8(sample)})
-                case 9..=16:
-                    first_byte := u8(sample & 0xFF)
-                    second_byte := u8((sample >> 8) & 0xFF)
-                    md5.update(&md5_ctx, {first_byte, second_byte})
-                case 17..=24:
-                    first_byte := u8(sample & 0xFF)
-                    second_byte := u8((sample >> 8) & 0xFF)
-                    third_byte := u8((sample >> 16) & 0xFF)
-                    md5.update(&md5_ctx, {first_byte, second_byte, third_byte})
-                case 25..=32:
-                    data := transmute([4]u8)sample
-                    md5.update(&md5_ctx, data[:])
-                case:
-                    fmt.println("INVALID BPS")
-                    os.exit(1)
-            }
-        }
-    }
-
-    // TODO: We need a way to copy (or better yet just point to) the decoded sample data
-    // We'll probably either copy each subframe's samples somehow, or have a dynamic array and append to that.
-    // Both are slow-ish but I can't think of a faster way that just works.
-    // This doesn't work btw, just for my future self to not think this is fine.
-    for subframe in subframes {
-        copy(flac.samples, subframe)
-    }
-
-    //
-    // Frame Footer
-    //
-    frame_end := r.i
-    frame_crc := read_data(r, u16be) or_return
-    calculated_frame_crc := calculate_crc16(r.s[frame_beginning:frame_end])
-
-    if auto_cast frame_crc != calculated_frame_crc {
-        fmt.eprintfln("Expected frame CRC 0x%X, got 0x%X", frame_crc, calculated_frame_crc)
-        return .CRC_Mismatch
-    }
-
-    frame_num += 1
-
-    return nil
 }
 
-load_from_bytes :: proc(data: []byte, options := Options{}, allocator := context.allocator) -> (flac: ^Flac, err: Error) {
+@(private)
-    r: Reader
+read_metadata :: proc(r: ^Reader, buffered := false, allocator := context.allocator) -> (flac: ^Flac, err: Error) {
-    bytes.reader_init(&r, data)
+    header := read_data(r, FlacHeader) or_return
-
-    md5.init(&md5_ctx)
-    defer md5.reset(&md5_ctx)
-
-    header := read_data(&r, FlacHeader) or_return
     if header.magic != FLAC_MAGIC {
         return nil, .Invalid_Signature
     }
@@ -718,7 +713,7 @@ load_from_bytes :: proc(data: []byte, options := Options{}, allocator := context
     pictures := make([dynamic]Picture, 0, 2, allocator)
     last_block := streaminfo_header.last_block
     for !last_block {
-        md_block_hdr := read_data(&r, u32be) or_return
+        md_block_hdr := read_data(r, u32be) or_return
         metadata_block_header := MetadataBlockHeader {
             last_block = bool(md_block_hdr >> 31),
             type       = BlockType((md_block_hdr >> 24) & 0x7F),
@@ -731,70 +726,95 @@ load_from_bytes :: proc(data: []byte, options := Options{}, allocator := context
             case .STREAMINFO:
                 // Do nothing, we already parse the mandatory streaminfo metadata
             case .PADDING:
-                //fmt.printfln("Skipping %d bytes of padding data", metadata_block_header.length)
+                if buffered {
-                bytes.reader_seek(&r, auto_cast metadata_block_header.length, .Current)
+                    reader := cast(^bufio.Reader)r.data
+                    skipped := bufio.reader_discard(reader, int(metadata_block_header.length)) or_return
+                } else {
+                    reader := cast(^bytes.Reader)r.data
+                    skipped := bytes.reader_seek(reader, i64(metadata_block_header.length), .Current) or_return
+                }
             case .APPLICATION:
                 //app_id := read_slice(&r, 4) or_return
                 //fmt.println("Found application with ID:", string(app_id))
                 //fmt.printfln("Skipping %d bytes of application metadata block", metadata_block_header.length)
-                bytes.reader_seek(&r, auto_cast metadata_block_header.length, .Current)
                 // TODO: handle the application data
+                if buffered {
+                    reader := cast(^bufio.Reader)r.data
+                    skipped := bufio.reader_discard(reader, int(metadata_block_header.length)) or_return
+                } else {
+                    reader := cast(^bytes.Reader)r.data
+                    skipped := bytes.reader_seek(reader, i64(metadata_block_header.length), .Current) or_return
+                }
             case .SEEKTABLE:
-                // TODO: check for size mismatch?
                 seekpoints := metadata_block_header.length / 18
                 //fmt.printfln("we have %d seekpoints", seekpoints)
+                actual_size := 0
                 for i in 0..<seekpoints {
-                    _ = read_data(&r, Seekpoint) or_return
+                    _ = read_data(r, Seekpoint) or_return
+                    actual_size += size_of(Seekpoint)
                     //fmt.println(seekpoint)
                 }
+
+                if metadata_block_header.length != u32(actual_size) {
+                    fmt.eprintln("Seektable metadata header length mismatch!")
+                    fmt.eprintfln("Expected size: %d, Got %d", metadata_block_header.length, actual_size)
+                }
             case .VORBIS_COMMENT:
-                // TODO: save this info to a struct
+                vendor_name_len := read_data(r, u32le) or_return
-                vendor_name_len := read_data(&r, u32le) or_return
+                vendor_name_slice := make([]byte, vendor_name_len)
-                vendor_name := string(read_slice(&r, auto_cast vendor_name_len) or_return)
+                read_slice(r, vendor_name_slice) or_return
-                user_comment_list_len := read_data(&r, u32le) or_return
+                vendor_name := string(vendor_name_slice)
+                user_comment_list_len := read_data(r, u32le) or_return
 
                 actual_size := 4 + vendor_name_len + 4
 
+                comments := make([]string, user_comment_list_len)
                 for i in 0..<user_comment_list_len {
-                    comment_len := read_data(&r, u32le) or_return
+                    comment_len := read_data(r, u32le) or_return
-                    comment := string(read_slice(&r, auto_cast comment_len) or_return)
+                    comment_slice := make([]byte, comment_len)
-                    //fmt.println(comment)
+                    read_slice(r, comment_slice) or_return
+                    comment := string(comment_slice)
                     actual_size += 4 + comment_len
+
+                    comments[i] = comment
                 }
+                flac.metadata.vorbis_comments = comments
+                flac.metadata.vendor_name = vendor_name
                 if metadata_block_header.length != u32(actual_size) {
-                    // TODO: should this be a warning instead of an error that halts the decoding?
+                    fmt.eprintln("Vorbis metadata header length mismatch!")
-                    // I think so, the comment isn't crucial to the decoding process.
+                    fmt.eprintfln("Expected size: %d, Got %d", metadata_block_header.length, actual_size)
-                    //fmt.println("Metadata header length mismatch!")
-                    //fmt.printfln("Expected size: %d, Got %d", metadata_block_header.length, actual_size)
-                    return flac, .Metadata_Block_Length_Mismatch
                 }
                 // TODO: framing bit??
-                //fmt.println(vendor_name)
             case .CUESHEET:
                 // TODO: save this to a struct
                 // + there's some CD-DA stuff that we need to consider I think
-                cuesheet := read_data(&r, CueSheet) or_return
+                cuesheet := read_data(r, CueSheet) or_return
                 if cuesheet.num_tracks < 1 {
                     // TODO: should this be a warning instead of an error that halts the decoding?
                     return flac, .Missing_Lead_Out_Track
                 }
                 //fmt.println(cuesheet)
                 for i in 0..<cuesheet.num_tracks {
-                    track := read_data(&r, CueSheetTrack) or_return
+                    track := read_data(r, CueSheetTrack) or_return
                     for i in 0..<track.num_track_index_points {
-                        _ = read_data(&r, CueSheetTrackIndex) or_return
+                        _ = read_data(r, CueSheetTrackIndex) or_return
                         //fmt.println(track_index)
                     }
                     //fmt.println(track)
                 }
             case .PICTURE:
-                pic_type := PictureType(read_data(&r, u32be) or_return)
+                pic_type := PictureType(read_data(r, u32be) or_return)
-                mime_len := read_data(&r, u32be) or_return
+                mime_len := read_data(r, u32be) or_return
-                mimetype := string(read_slice(&r, auto_cast mime_len) or_return)
+                mimetype_slice := make([]byte, mime_len)
-                desc_len := read_data(&r, u32be) or_return
+                read_slice(r, mimetype_slice) or_return
-                desc := string(read_slice(&r, auto_cast desc_len) or_return)
+                mimetype := string(mimetype_slice)
-                metadata := read_data(&r, PictureMetadata) or_return
+                desc_len := read_data(r, u32be) or_return
-                data := read_slice(&r, auto_cast metadata.data_len) or_return
+                desc_slice := make([]byte, desc_len)
+                read_slice(r, desc_slice) or_return
+                desc := string(desc_slice)
+                metadata := read_data(r, PictureMetadata) or_return
+                data := make([]byte, metadata.data_len)
+                read_slice(r, data) or_return
                 picture := Picture{
                     type = pic_type,
                     mimetype = mimetype,
@@ -808,40 +828,334 @@ load_from_bytes :: proc(data: []byte, options := Options{}, allocator := context
                 append(&pictures, picture)
             case .INVALID:
                 fmt.eprintln("Invalid block type")
-                bytes.reader_seek(&r, auto_cast metadata_block_header.length, .Current)
+                if buffered {
+                    reader := cast(^bufio.Reader)r.data
+                    skipped := bufio.reader_discard(reader, int(metadata_block_header.length)) or_return
+                } else {
+                    reader := cast(^bytes.Reader)r.data
+                    skipped := bytes.reader_seek(reader, i64(metadata_block_header.length), .Current) or_return
+                }
             case:
                 fmt.printfln("Skipping %d bytes of Unknown metadata block", metadata_block_header.length)
-                bytes.reader_seek(&r, auto_cast metadata_block_header.length, .Current)
+                if buffered {
+                    reader := cast(^bufio.Reader)r.data
+                    skipped := bufio.reader_discard(reader, int(metadata_block_header.length)) or_return
+                } else {
+                    reader := cast(^bytes.Reader)r.data
+                    skipped := bytes.reader_seek(reader, i64(metadata_block_header.length), .Current) or_return
                 }
         }
-
-    // Yucky
-    err = decode_frame(&r, flac)
-    for err == nil {
-        err = decode_frame(&r, flac)
     }
 
     flac.metadata.pictures = pictures[:]
 
+    return flac, nil
+}
+
+read_next_frame :: proc(r: ^Reader, flac: ^Flac) -> (frame: Frame, err: Error) {
+    //
+    // Frame Header
+    //
+    tee_r: io.Tee_Reader
+    crc_buffer: bytes.Buffer
+    bytes.buffer_init_allocator(&crc_buffer, 0, 128)
+    defer bytes.buffer_destroy(&crc_buffer)
+    crc := bytes.buffer_to_stream(&crc_buffer)
+    r := &Reader{
+        r = io.tee_reader_init(&tee_r, r, crc),
+        buf = r.buf,
+        x = r.x,
+        n = r.n,
+    }
+
+    data := read_data(r, u16be) or_return
+
+    sync_code := data >> 2
+    blocking_strategy := BlockingStrategy(data & 1)
+
+    data = read_data(r, u16be) or_return
+    block_size := data >> 12
+    sample_rate := SampleRate((data >> 8) & 0xF)
+    channel_assignment := ChannelAssignment((data >> 4) & 0xF)
+    sample_size := SampleSize((data >> 1) & 7)
+
+    coded_num := decode_extended_utf8(r) or_return
+    if blocking_strategy == .VARIABLE {
+        // Sample number of first sample
+        // MUST NOT be larger than 36 bits unencoded or 7 bytes encoded.
+        // MUST be equal to the number of samples preceding the current frame. Otherwise seeking is not possible.
+        // TODO: also write a check for the number of samples so we'll probably keep track of how many samples we decoded
+        // maybe the number of decoded samples can be inferred by the number of frames ?? or just use the length of 
+        // the decoded_samples slice.
+        if coded_num > 0x1000000000 {
+            // TODO: Sample number can't be bigger than 36 bits
+        }
+    } else {
+        // Frame number
+        // MUST NOT be larger than 31 bits unencoded or 6 bytes encoded.
+        // MUST be equal to the number of frames preceding the current frame. Otherwise seeking is not possible.
+        // TODO: also write a check for the number of frames so we'll probably keep track of how many frames we decoded.
+        if coded_num > 0x80000000 {
+            // TODO: Frame number cannot be bigger than 31 bits
+        }
+    }
+
+    actual_block_size: u16be
+    switch block_size {
+        case 1:
+            actual_block_size = 192
+        case 2..=5:
+            actual_block_size = 576 * auto_cast (pow2(block_size - 2))
+        case 6:
+            actual_block_size = auto_cast (read_bits(r, 8) or_return) + 1
+        case 7:
+            actual_block_size = (read_data(r, u16be) or_return) + 1
+        case 8..=15:
+            actual_block_size = 256 * auto_cast (pow2(block_size - 8))
+        case:
+            return {}, .Invalid_Block_Size
+    }
+
+    //if actual_block_size < 15 && !last_frame {
+        // TODO: block sizes less than 16 are only valid for the last frame and MUST NOT be used for any other frame.
+    //}
+
+    actual_sample_rate_in_Hz: u32
+    switch sample_rate {
+        case .USE_STREAMINFO:
+            actual_sample_rate_in_Hz = flac.metadata.sample_rate
+        case ._88_2kHz:
+            actual_sample_rate_in_Hz = 88200
+        case ._176_4kHz:
+            actual_sample_rate_in_Hz = 176400
+        case ._192kHz:
+            actual_sample_rate_in_Hz = 192000
+        case ._8kHz:
+            actual_sample_rate_in_Hz = 8000
+        case ._16kHz:
+            actual_sample_rate_in_Hz = 16000
+        case ._22_05kHz:
+            actual_sample_rate_in_Hz = 22005
+        case ._24kHz:
+            actual_sample_rate_in_Hz = 24000
+        case ._32kHz:
+            actual_sample_rate_in_Hz = 32000
+        case ._44_1kHz:
+            actual_sample_rate_in_Hz = 44100
+        case ._48kHz:
+            actual_sample_rate_in_Hz = 48000
+        case ._96kHz:
+            actual_sample_rate_in_Hz = 96000
+        case .USE_8_BITS_IN_kHz_FROM_HEADER_END:
+            actual_sample_rate_in_Hz = auto_cast (read_bits(r, 8) or_return) * 1000
+        case .USE_16_BITS_IN_Hz_FROM_HEADER_END:
+            actual_sample_rate_in_Hz = auto_cast (read_data(r, u16be) or_return)
+        case .USE_16_BITS_IN_TENS_OF_Hz_FROM_HEADER_END:
+            actual_sample_rate_in_Hz = auto_cast (read_data(r, u16be) or_return) * 10
+        case .INVALID: fallthrough
+        case:
+            return {}, .Invalid_Sample_Rate
+    }
+
+    // TODO: sample rate MUST NOT be 0 if the subframe contains audio.
+    // a sample rate of 0 MAY be used when non-audio is represented.
+
+    crc8_bytes := bytes.buffer_to_bytes(&crc_buffer)
+    frame_header_crc := u8(read_bits(r, 8) or_return)
+    calculated_header_crc := calculate_crc8(crc8_bytes)
+
+    if frame_header_crc != calculated_header_crc {
+        fmt.printfln("Expected frame header CRC: 0x%X, got: 0x%X", frame_header_crc, calculated_header_crc)
+        return {}, .CRC_Mismatch
+    }
+
+    //
+    // Subframes
+    //
+    bps: u8
+    switch sample_size {
+        case .USE_STREAMINFO:
+            bps = flac.metadata.bits_per_sample
+        case ._8BPS:
+            bps = 8
+        case ._12BPS:
+            bps = 12
+        case ._16BPS:
+            bps = 16
+        case ._20BPS:
+            bps = 20
+        case ._24BPS:
+            bps = 24
+        case ._32BPS:
+            bps = 32
+    }
+
+    if bps != flac.metadata.bits_per_sample {
+        return {}, .Bits_Per_Second_Mismatch
+    }
+
+    frame_channels := flac.metadata.channels
+    switch channel_assignment {
+        case .MONO:
+            frame_channels = 1
+        case ._3CHANNELS:
+            frame_channels = 3
+        case ._4CHANNELS:
+            frame_channels = 4
+        case ._5CHANNELS:
+            frame_channels = 5
+        case ._6CHANNELS:
+            frame_channels = 6
+        case ._7CHANNELS:
+            frame_channels = 7
+        case ._8CHANNELS:
+            frame_channels = 8
+        case ._2CHANNELS: fallthrough
+        case .STEREO_LEFT_SIDE: fallthrough
+        case .STEREO_SIDE_RIGHT: fallthrough
+        case .STEREO_MID_SIDE:
+            frame_channels = 2
+    }
+
+    if frame_channels != flac.metadata.channels {
+        // TODO: warning or error?
+        // we have a faulty file that says it has 5 channels but subframes all say they got 1
+        // we also have an two uncommon files with increasing and decreasing number of channels
+        // uncommon are supposed to be unusual but still valid FLAC files. why is that first one faulty then???
+        // so many questions...
+    }
+
+    subframes := make([][]i32, frame_channels)
+    defer delete(subframes)
+    for i in 0..<frame_channels {
+        frame_bps := bps
+        // For side channels we increase the bps by 1
+        // Left, mid and right channels don't need an extra bit.
+        // ref: https://github.com/ietf-wg-cellar/flac-specification/blob/master/rfc_backmatter.md#first-audio-frame
+        if (channel_assignment == .STEREO_SIDE_RIGHT && i == 0) ||
+           ((channel_assignment == .STEREO_LEFT_SIDE || channel_assignment == .STEREO_MID_SIDE) && i == 1) {
+            frame_bps += 1
+        }
+
+        subframes[i] = decode_subframe(r, frame_bps, auto_cast actual_block_size) or_return
+    }
+
+    align_to_byte(r)
+
+    correlate(subframes, channel_assignment)
+
+    samples_arr := make([dynamic]i32, 0, block_size * 2)
+    // Write the samples interleaved.
+    for i in 0..<len(subframes[0]) {
+        for subframe, sf in subframes {
+            sample := subframe[i]
+            append(&samples_arr, sample)
+        }
+    }
+
+    for subframe in subframes {
+        delete(subframe)
+    }
+
+    frame.samples = samples_arr[:]
+    frame.channels = frame_channels
+    frame.sample_rate = actual_sample_rate_in_Hz
+
+    //
+    // Frame Footer
+    //
+    crc16_bytes := bytes.buffer_to_bytes(&crc_buffer)
+    frame_crc := u16(read_data(r, u16be) or_return)
+    calculated_frame_crc := calculate_crc16(crc16_bytes)
+
+    if frame_crc != calculated_frame_crc {
+        fmt.eprintfln("Expected frame CRC 0x%X, got 0x%X", frame_crc, calculated_frame_crc)
+        return {}, .CRC_Mismatch
+    }
+
+    return frame, nil
+}
+
+md5hash :: proc(md5_ctx: ^md5.Context, bps: u8, samples: []i32) {
+    for sample in samples {
+        switch bps {
+            case 1..=8:
+                md5.update(md5_ctx, {u8(sample)})
+            case 9..=16:
+                first_byte := u8(sample & 0xFF)
+                second_byte := u8((sample >> 8) & 0xFF)
+                md5.update(md5_ctx, {first_byte, second_byte})
+            case 17..=24:
+                first_byte := u8(sample & 0xFF)
+                second_byte := u8((sample >> 8) & 0xFF)
+                third_byte := u8((sample >> 16) & 0xFF)
+                md5.update(md5_ctx, {first_byte, second_byte, third_byte})
+            case 25..=32:
+                data := transmute([4]u8)sample
+                md5.update(md5_ctx, data[:])
+            case:
+                fmt.println("INVALID BPS")
+                os.exit(1)
+        }
+    }
+}
+
+md5sum :: proc(md5_ctx: ^md5.Context, flac: ^Flac) -> Error {
+    calculated_md5: [16]byte
+    md5.final(md5_ctx, calculated_md5[:])
+
+    flac.metadata.calculated_md5 = calculated_md5
+
+    if mem.compare(calculated_md5[:], flac.metadata.expected_md5[:]) != 0 {
+        return .MD5_Mismatch
+    }
+
+    return nil
+}
+
+// `load_from_bytes` takes a byte slice and initializes a bitreader for it.
+// The data is expected to be a full flac stream.
+load_from_bytes :: proc(data: []byte, options := Options{}, allocator := context.allocator) -> (flac: ^Flac, err: Error) {
+    context.allocator = allocator
+
+    byte_r: bytes.Reader
+    bytes.reader_init(&byte_r, data)
+
+    r := Reader{bytes.reader_to_stream(&byte_r), 0, 0, 0}
+
+    flac = read_metadata(&r) or_return
+    if .only_return_metadata in options {
+        return flac, nil
+    }
+
+    md5_ctx: md5.Context
+    md5.init(&md5_ctx)
+    defer md5.reset(&md5_ctx)
+
+    for {
+        err = decode_frame(&r, flac, &md5_ctx, options)
+        if err != nil {
+            if err == .EOF {
+                break
+            } else {
+                return flac, err
+            }
+        }
+    }
+
     if err != .EOF {
         return flac, err
     }
 
-    //
+    if .skip_md5_check not_in options {
-    // Validate the decoded audio data's md5
+        md5sum(&md5_ctx, flac) or_return
-    //
-    calculated_md5: [16]byte
-    md5.final(&md5_ctx, calculated_md5[:])
-
-    flac.metadata.calculated_md5 = calculated_md5
-
-    if mem.compare(calculated_md5[:], header.streaminfo.md5[:]) != 0 {
-        return flac, .MD5_Mismatch
     }
 
     return flac, nil
 }
 
+// `load_from_file` reads the entire file to memory and operates on the returned byte slice.
+// Only use this with small files.
 load_from_file :: proc(filename: string, options := Options{}, allocator := context.allocator) -> (flac: ^Flac, err: Error) {
     context.allocator = allocator
 
@@ -849,22 +1163,71 @@ load_from_file :: proc(filename: string, options := Options{}, allocator := cont
     defer delete(data)
 
     if ok {
-        return load_from_bytes(data)
+        return load_from_bytes(data, options)
     } else {
         return nil, .Unable_To_Read_File
     }
 }
 
-destroy :: proc(flac: ^Flac) {
+
-    // TODO: clean up the allocations
+// `load_from_file_buffered` initializes a buffered reader for the file and reads all the metadata blocks.
-    delete(flac.samples)
+// Calls to `read_next_frame()` MUST be made to decode the audio data.
-    // TODO: I think this data gets deleted when the data from os.read_entire_file is deleted.
+// This is the recommended way to read most FLAC files as it has a minimal memory overhead.
-    // Double check that and if it's true then make sure to copy this data.
+load_from_file_buffered :: proc(filename: string, allocator := context.allocator) -> (flac: ^Flac, r: ^Reader, err: Error) {
-    // Copying small strings is fine but copying the image pixel data might be slow.
+    context.allocator = allocator
-    //for picture in flac.metadata.pictures {
+
-    //    picture.mimetype
+    file, open_err := os.open(filename)
-    //    picture.data
+    if open_err != os.ERROR_NONE {
-    //    picture.description
+        fmt.eprintln(open_err)
-    //}
+        return nil, {}, .Unable_To_Read_File
-    delete(flac.metadata.pictures)
+    }
+
+    br := new(bufio.Reader)
+    bufio.reader_init(br, os.stream_from_handle(file))
+
+    r = new(Reader)
+    r.r = bufio.reader_to_stream(br)
+    r.buf = 0
+    r.x = 0
+    r.n = 0
+
+    flac = read_metadata(r, true) or_return
+
+    return flac, r, nil
+}
+
+/* `destroy` cleans up and frees the memory allocated by all 3 loading functions.
+ The returned reader from `load_from_file_buffered` MUST be passed to `destroy` in order to close the file handle.
+ `load_from_file` and `load_from_bytes` may pass nil as the reader.
+ ---
+ The allocator that was used when loading the flac file MUST be passed to `destroy` in order to properly free
+ the memory, otherwise a bad free may occur and crash the program.
+*/
+destroy :: proc(flac: ^Flac, r: ^Reader = nil, allocator := context.allocator) {
+    context.allocator = allocator
+
+    delete(flac.samples)
+    for picture in flac.metadata.pictures {
+        delete(picture.mimetype)
+        delete(picture.data)
+        delete(picture.description)
+    }
+    delete(flac.metadata.pictures)
+
+    for comment in flac.metadata.vorbis_comments {
+        delete(comment)
+    }
+    delete(flac.metadata.vorbis_comments)
+    delete(flac.metadata.vendor_name)
+
+    free(flac)
+
+    if r != nil {
+        br := cast(^bufio.Reader)r.data
+        closer, ok := io.to_closer(br.rd)
+        io.close(closer)
+        bufio.reader_destroy(br)
+        free(br)
+        free(r)
+    }
 }

internal.odin

@@ -79,11 +79,6 @@ crc16_lookup := [256]u16 {
 
 fixed_coefficients := [4][]i32{{1}, {2, -1}, {3, -3, 1}, {4, -6, 4, -1}}
 
-// TODO: no idea if I want to keep this global and a thread_local
-// or if I should just init it in load_from_bytes
-@(thread_local)
-md5_ctx: md5.Context
-
 BlockType :: enum u16be {
     STREAMINFO,
     PADDING,
@@ -253,7 +248,7 @@ decode_extended_utf8 :: proc(r: ^Reader) -> (decoded_num: u64, err: Error) {
 
     decoded_num = u64(0)
 
-    first_byte := read_byte(r) or_return
+    first_byte := read_bits(r, 8) or_return
     utf8_sequence_len := 0
 
     for i: uint = 7; i > 0; i -= 1 {
@@ -269,7 +264,7 @@ decode_extended_utf8 :: proc(r: ^Reader) -> (decoded_num: u64, err: Error) {
         octets := make([dynamic]byte, 0, 8)
         defer delete(octets)
         for i := utf8_sequence_len - 1; i > 0; i -= 1 {
-            append(&octets, read_byte(r) or_return)
+            append(&octets, byte(read_bits(r, 8) or_return))
         }
 
         switch utf8_sequence_len {

reader.odin

@@ -8,119 +8,85 @@ import "core:io"
  Uses core:bytes reader under the hood with a few useful procedures for reading structs and other types.
 */
 Reader :: struct {
-    using _:   bytes.Reader,
+    using r: io.Stream,
-    bits_read: u8,
+    // Temporary read buffer.
+    buf: [8]u8,
+    // Between 0 and 7 buffered bits since previous read operations.
+    x: u8,
+    // The number of buffered bits in x.
+    n: uint,
 }
 
-read_slice :: #force_inline proc(r: ^Reader, size: int) -> (res: []u8, err: io.Error) {
+read_slice :: #force_inline proc(r: ^Reader, buf: []u8) -> io.Error {
-    #no_bounds_check {
+    io.read_full(r^, buf) or_return
-        if r.i + i64(size) <= i64(len(r.s)) {
-            res = r.s[r.i:r.i + i64(size)]
-            r.i += i64(size)
-            return res, .None
-        }
-    }
 
-    if i64(len(r.s)) == r.i {
+    return nil
-        return []u8{}, .EOF
-    } else {
-        return []u8{}, .Short_Buffer
-    }
 }
 
 read_data :: #force_inline proc(r: ^Reader, $T: typeid) -> (res: T, err: io.Error) {
-    b := read_slice(r, size_of(T)) or_return
+    b: [size_of(T)]byte
+    read_slice(r, b[:]) or_return
+
     return (^T)(&b[0])^, nil
 }
 
-read_bit :: proc(r: ^Reader) -> (bit: byte, err: Error) #no_bounds_check {
+// Read reads and returns the next n bits, at most 64. It buffers bits up to the
-    if r.i >= i64(len(r.s)) {
+// next byte boundary.
-        return 0, .EOF
+// Borrowed from https://github.com/mewkiz/flac
+read_bits :: proc(r: ^Reader, n: uint) -> (res: u64, err: io.Error) #no_bounds_check {
+    if n == 0 {
+        return 0, nil
     }
 
-    bits := 8 - (r.bits_read + 1)
+    n := n
-    b := (r.s[r.i] >> bits) & 1
-    r.bits_read += 1
 
-    if r.bits_read == 8 {
+    // Read buffered bits.
-        r.i += 1
+    if r.n > 0 {
-        r.bits_read = 0
+        switch {
-    }
+        case r.n == n:
-
+            r.n = 0
-    return b, nil
+            return u64(r.x), nil
-}
+        case r.n > n:
-
+            r.n -= n
-read_bits :: proc(r: ^Reader, n: uint) -> (bits: u64, err: Error) #no_bounds_check {
+            mask := ~u8(0) << r.n
-    res: u64
+            res = u64(r.x&mask) >> r.n
-
+            r.x &~= mask
-    // Fast path: if we can read all bits within the current byte.
-    if r.bits_read + u8(n) <= 8 {
-        res = (u64(r.s[r.i]) >> (8 - r.bits_read - u8(n))) & ((1 << n) - 1)
-        r.bits_read += u8(n)
-        if r.bits_read == 8 {
-            r.bits_read = 0
-            r.i += 1
-        }
             return res, nil
         }
-
+        n -= r.n
-    // General case: reading across multiple bytes.
+        res = u64(r.x)
-    rem_bits := n
+        r.n = 0
-    if r.bits_read > 0 {
-        // Read the remaining bits in the current byte.
-        bits_in_byte := 8 - r.bits_read
-        res = u64(r.s[r.i]) & ((1 << bits_in_byte) - 1)
-        rem_bits -= uint(bits_in_byte)
-        r.bits_read = 0
-        r.i += 1
     }
 
-    // Read full bytes.
+    // Fill the temporary buffer.
-    for rem_bits >= 8 {
+    bytes := n / 8
-        res = (res << 8) | u64(r.s[r.i])
+    bits := n % 8
-        rem_bits -= 8
+    if bits > 0 {
-        r.i += 1
+        bytes += 1
     }
+    io.read_full(r, r.buf[:bytes]) or_return
 
-    // Read remaining bits in the final byte.
+    // Read bits from the temporary buffer.
-    if rem_bits > 0 {
+    for b in r.buf[:bytes-1] {
-        res = (res << rem_bits) | (u64(r.s[r.i]) >> (8 - rem_bits))
+        res <<= 8
-        r.bits_read += u8(rem_bits)
+        res |= u64(b)
     }
-
+    b := r.buf[bytes-1]
-    return res, nil
+    if bits > 0 {
-}
+        res <<= bits
-
+        r.n = 8 - bits
-read_byte :: proc(r: ^Reader) -> (b: byte, err: Error) #no_bounds_check {
+        mask := ~u8(0) << r.n
-    if r.i >= i64(len(r.s)) {
+        res |= u64(b&mask) >> r.n
-        return 0, .EOF
+        r.x = b & ~mask
-    }
-    // Continue reading from the current byte if it has unread bits.
-    if r.bits_read != 0 {
-        cur_byte := r.s[r.i]
-        next_byte := r.s[r.i + 1]
-        rem_bits := 8 - r.bits_read
-        rem_bits_mask: u8 = (1 << rem_bits) - 1
-        b = ((cur_byte & rem_bits_mask) << r.bits_read) | (next_byte >> rem_bits)
-        r.i += 1
     } else {
-        b = r.s[r.i]
+        res <<= 8
-        r.i += 1
+        res |= u64(b)
     }
-    return b, nil
+
+    return res, nil
 }
 
-align_to_byte :: proc(r: ^Reader) -> Error {
+align_to_byte :: proc(r: ^Reader) {
-    if r.bits_read == 0 {
+    r.x = 0
-        return nil
+    r.n = 0
-    }
-    if r.i >= i64(len(r.s)) {
-        return .EOF
-    }
-
-    // Align by skipping the remaining bits in the byte
-    r.bits_read = 0
-    r.i += 1
-
-    return nil
 }