@ ARM assembly for binary tree search with cdr-coding for
        @ left-subtree pointers

        .syntax unified
        .cpu cortex-m4
        .globl tsearch
        .thumb_func
        .thumb
tsearch:    tst r1, r1
            beq notfound
    1:      ldr r2, [r1], #8  @ point to following entry (no postincrement on Thumb-1)
            cmp r0, r2
            beq found
            blo 1b            @ if lower, continue inner loop
            ldr r1, [r1, -4]  @ negative offset, not on Thumb-1
            b.n tsearch

etsearch:   tst r1, r1
            beq notfound
            add r1, r3        @ offset pointer by the file base address
    1:      ldr r2, [r1], #8
            cmp r0, r2
            blo 1b
            beq found
            ldr r1, [r1, #-4]
            b etsearch

estsearch:  sub r4, #7         @ adjust end of file
    2:      tst r1, r1
            beq notfound
            add r1, r3
    1:      cmp r1, r4         @ check each pointer against end of file
            bhs outofbounds    @ if pair not inside file, crap out here
            ldr r2, [r1], #8
            cmp r0, r2
            blo 1b
            beq found
            ldr r1, [r1, #-4]
            b 2b

separator:      

    2:      ldr r1, [r1, #-4]    @ right-subtree case: load pointer
stsearch:   tst r1, r1           @ check pointer for null
            beq notfound
    1:      ldr r2, [r1], #8
            cmp r0, r2
            blo 1b
            bhi 2b
            b found

sep2:   

    2:      ldr r1, [r1, #-4]
zsearch:    cbz r1, notfound
    1:      ldr r2, [r1], #8
            cmp r0, r2
            blo 1b
            bhi 2b
            b found

notfound:       nop


        @ Hypothetically dynamically-generated code for a couple of tree nodes:
tree:   
        movw r2, #0x38a3
        cmp r0, r2
        beq.n found
        bhi 1f                @ branch to right subtree

        movw r2, #0x2023
        cmp r0, r2
        beq.n found
        bhi 2f                @ branch to right subtree

1:      nop
2:      nop