;;
;; aPLib compression library  -  the smaller the better :)
;;
;; TASM / MASM / WASM assembler depacker
;;
;; Copyright (c) 1998-2000 by Joergen Ibsen / Jibz
;; All Rights Reserved
;;

.CODE


_aP_depack_asm proc
    pushad

    mov    esi, [esp + 36]    ; C calling convention
    mov    edi, [esp + 40]

    cld
    mov    dl, 80h

literal:
    movsb
nexttag:
    call   getbit
    jnc    literal

    xor    ecx, ecx
    call   getbit
    jnc    codepair
    xor    eax, eax
    call   getbit
    jnc    shortmatch
    inc    ecx
    mov    al, 10h
getmorebits:
    call   getbit
    adc    al, al
    jnc    getmorebits
    jnz    domatch
    stosb
    jmp    short nexttag
codepair:
    call   getgamma_no_ecx
    dec    ecx
    loop   normalcodepair
    call   getgamma
    jmp    short domatch_lastpos

shortmatch:
    lodsb
    shr    eax, 1
    jz     donedepacking
    adc    ecx, ecx
    jmp    short domatch_with_2inc

normalcodepair:
    xchg   eax, ecx
    dec    eax
    shl    eax, 8
    lodsb
    call   getgamma
    cmp    eax, 32000
    jae    domatch_with_2inc
    cmp    ah, 5
    jae    domatch_with_inc
    cmp    eax, 7fh
    ja     domatch_new_lastpos

domatch_with_2inc:
    inc    ecx

domatch_with_inc:
    inc    ecx

domatch_new_lastpos:
    xchg   eax, ebp
domatch_lastpos:
    mov    eax, ebp

domatch:
    push   esi
    mov    esi, edi
    sub    esi, eax
    rep    movsb
    pop    esi
    jmp    short nexttag

getbit:
    add     dl, dl
    jnz     stillbitsleft
    mov     dl, [esi]
    inc     esi
    adc     dl, dl
stillbitsleft:
    ret

getgamma:
    xor    ecx, ecx
getgamma_no_ecx:
    inc    ecx
getgammaloop:
    call   getbit
    adc    ecx, ecx
    call   getbit
    jc     getgammaloop
    ret

donedepacking:
    sub    edi, [esp + 40]
    mov    [esp + 28], edi    ; return unpacked length in eax

    popad
    ret

_aP_depack_asm endp