ls-arm/string.S

/*
    @args:
        r1 => pointer to the string
    @returns:
        r0 => string length
    @clobbers:
        r2
*/
bytelen:
    mov r0, #0
1:
    ldrb r2, [r1, r0]
    cmp r2, #0
    bxle lr

    add r0, r0, #1
    b 1b

/*
    @args:
        r1 => pointer to first string
        r2 => pointer to second string
    @returns:
        r0 => 0 if equal, -1 if a < b, 1 if a > b
    @clobbers:
        r1, r2, r3
*/
strcmp_ascii:
@ comparison loop
1:
    ldrb r0, [r1], #1
    ldrb r3, [r2], #1
    cmp r0, r3
    bne 2f
    cmp r0, #0
    bne 1b

    @ strings are equal
    mov r0, #0
    bx lr

@ if we found a different byte then return the appropriate integer
2:
    sub r0, r0, r3
    cmp r0, #0
    movlt r0, #-1
    movgt r0, #1
    bx lr