wavcrc32: Программа для проверки CRC аудиоданных, или о том, как EAC считает CRC (обсуждение)

Greetings!
Some time ago I noticed the strange behaviour of EAC CRC calculator
that is built in "WAVE Editor" feature (Tools->Process WAV...),
depending on checkbox "No use of null samples in CRC calculations".
1. when this checkbox is unchecked, EAC uses all samples to calculate CRC
while ripping CDs and while processing WAV files in WAVE editor.
So, if we "process" ripped image in WAV editor, we'll see that CRC
in .LOG-file and "Checksum" in the UL-corner of "WAVE Editor" are the
same. No problem.
But
2. when this checkbox is checked, the values that we obtain in .LOG-file
and in "WAVE Editor" during ripped image file processing do NOT MATCH!
This result is stable, so it does not depend on what disc we're
ripping and so on. I use WAV Editor when checking CRC on non-mine
rips, so this mismatch is annoying.
In the programmer terms, let RIP_CRC(bool bUseFlag) be the macro that calculates CRC
while ripping CDs, and WAV_ED_CRC(bool bUseFlag) be the macro that
calculates CRC in WAVE Editor. The parameter bUseFlag is the "No use
of nul samples..." checkbox state.
So, in these terms, we have that
RIP_CRC(false) = WAV_ED_CRC(false)
RIP_CRC(true) != WAV_ED_CRC(true) (!!!)
I tried to discover, where is the error. And I hope I was lucky that
day. So, the solution of this inconsistency lies in the algorythm
of WAV_ED_CRC(true) that is buggy (!). And You may easily check this.
Take a stereo WAVe file, and calculate CRC using WAVE Editor. You gget
value CRC=X. Then, modify ANY nonzero sample on RIGHT channel of this file.
And then calculate it again. You get the SAME value X.
But, obviously, this cannot be true if the procedure works fine.
Saying in a wisper, I ought to hack/reverse your beautiful program!
And then I found that, indeed, the specified bug has place, in
WAV_ED_CRC(true) routine.
Here is the assembly of the WAV_ED_CRC(true) [buggy]
(the listing is from IDA Pro 5.0)

.text:0045E520 ; int __stdcall proc_CRC_Calc_BUF_Ignore_Word_Zeros_S1(int count,int p_CRC,int pBuffer,int old_CRC)
.text:0045E520 proc_CRC_Calc_BUF_Ignore_Word_Zeros_S1 proc near            ; CODE XREF: .text:00525BAFp
.text:0045E520
.text:0045E520 count               = dword ptr  8
.text:0045E520 p_CRC               = dword ptr  0Ch
.text:0045E520 pBuffer             = dword ptr  10h
.text:0045E520 old_CRC             = dword ptr  14h
.text:0045E520
.text:0045E520                     push ebp
.text:0045E521                     mov ebp, esp
.text:0045E523                     push ebx
.text:0045E524                     push esi
.text:0045E525                     push edi
.text:0045E526                     push eax
.text:0045E527                     push ebx
.text:0045E528                     push ecx
.text:0045E529                     push edx
.text:0045E52A                     push esi
.text:0045E52B                     push edi
.text:0045E52C                     mov esi, [ebp+old_CRC]
.text:0045E52F                     mov edi, [ebp+pBuffer]
.text:0045E532                     mov edx, [ebp+p_CRC]
.text:0045E535                     mov eax, [ebp+count]
.text:0045E538                     mov ecx, [edx]
.text:0045E53A
.text:0045E53A cycle:                                                      ; CODE XREF:
proc_CRC_Calc_BUF_Ignore_Word_Zeros_S1+5Bj
; ---------------------------------------------------------
; here we obtain
; only lower word of [edi], that is L-R-sample
; the higher word is unused
; ---------------------------------------------------------
.text:0045E53A                     mov bx, [edi]
.text:0045E53D                     cmp bx, 0
.text:0045E541                     jz  short end_if__1
.text:0045E543                     push eax
.text:0045E544                     push edx
.text:0045E545                     push ecx
.text:0045E546                     call proc_CRC_TwoByte_BX_ptr_ESI
.text:0045E54B                     pop ecx
.text:0045E54C                     pop edx
.text:0045E54D                     pop eax
.text:0045E54E                     mov bx, [edi]
.text:0045E551                     cmp bx, 32768
.text:0045E556                     jnz short end_if__0
.text:0045E558                     mov bx, 8001h
.text:0045E55C
.text:0045E55C end_if__0:                                                  ; CODE XREF:
proc_CRC_Calc_BUF_Ignore_Word_Zeros_S1+36j
.text:0045E55C                     cmp bx, cx
.text:0045E55F                     jle short end_if__1
.text:0045E561                     mov cx, bx
.text:0045E564
.text:0045E564 end_if__1:                                                  ; CODE XREF:
proc_CRC_Calc_BUF_Ignore_Word_Zeros_S1+21j
.text:0045E564                                                             ; proc_CRC_Calc_BUF_Ignore_Word_Zeros_S1+3Fj
.text:0045E564                     ror ecx, 10h
.text:0045E567                     cmp bx, cx
.text:0045E56A                     jge short end_if__2
.text:0045E56C                     mov cx, bx
.text:0045E56F
.text:0045E56F end_if__2:                                                  ; CODE XREF:
proc_CRC_Calc_BUF_Ignore_Word_Zeros_S1+4Aj
.text:0045E56F                     ror ecx, 10h
; ---------------------------------------------------------
; we increment EDI by 4, so we skip right (or left?) channel
; ---------------------------------------------------------
.text:0045E572                     add edi, 4
.text:0045E575                     sub eax, 1
.text:0045E578                     cmp eax, 0
.text:0045E57B                     jge short cycle
.text:0045E57D                     mov [edx], ecx
.text:0045E57F                     pop edi
.text:0045E580                     pop esi
.text:0045E581                     pop edx
.text:0045E582                     pop ecx
.text:0045E583                     pop ebx
.text:0045E584                     pop eax
.text:0045E585                     pop edi
.text:0045E586                     pop esi
.text:0045E587                     pop ebx
.text:0045E588                     pop ebp
.text:0045E589                     retn 10h
.text:0045E589 proc_CRC_Calc_BUF_Ignore_Word_Zeros_S1 endp
;
------------------------------------------------------------------------

And here is the assembly of the WAV_ED_CRC(false) [normal, non-buggy]

.text:0045E590 proc_CRC_Calc_BUF_NoIgnore_Word_Zeros_S2 proc near          ; CODE XREF: .text:0049E4AAp
.text:0045E590
.text:0045E590 arg_0               = dword ptr  8
.text:0045E590 arg_4               = dword ptr  0Ch
.text:0045E590 arg_8               = dword ptr  10h
.text:0045E590 arg_C               = dword ptr  14h
.text:0045E590
.text:0045E590                     push ebp
.text:0045E591                     mov ebp, esp
.text:0045E593                     push ebx
.text:0045E594                     push esi
.text:0045E595                     push edi
.text:0045E596                     push eax
.text:0045E597                     push ebx
.text:0045E598                     push ecx
.text:0045E599                     push edx
.text:0045E59A                     push esi
.text:0045E59B                     push edi
.text:0045E59C                     mov esi, [ebp+arg_C]
.text:0045E59F                     mov edi, [ebp+arg_8]
.text:0045E5A2                     mov edx, [ebp+arg_4]
.text:0045E5A5                     mov eax, [ebp+arg_0]
.text:0045E5A8                     mov ecx, [edx]
.text:0045E5AA
.text:0045E5AA loc_45E5AA:                                                 ; CODE XREF:
proc_CRC_Calc_BUF_NoIgnore_Word_Zeros_S2+5Ej
.text:0045E5AA                     push eax
.text:0045E5AB                     push edx
.text:0045E5AC                     push ecx
; -----------------------------------
; calculate left channel (lower word)
; -----------------------------------
.text:0045E5AD                     mov bx, [edi]
.text:0045E5B0                     call proc_CRC_TwoByte_BX_ptr_ESI
; -----------------------------------
; calculate left channel (high word)
; -----------------------------------
.text:0045E5B5                     mov bx, [edi+2]
.text:0045E5B9                     call proc_CRC_TwoByte_BX_ptr_ESI
.text:0045E5BE                     pop ecx
.text:0045E5BF                     pop edx
.text:0045E5C0                     pop eax
.text:0045E5C1                     mov bx, [edi]
.text:0045E5C4                     cmp bx, 8000h
.text:0045E5C9                     jnz short loc_45E5CF
.text:0045E5CB                     mov bx, 8001h
.text:0045E5CF
.text:0045E5CF loc_45E5CF:                                                 ; CODE XREF:
proc_CRC_Calc_BUF_NoIgnore_Word_Zeros_S2+39j
.text:0045E5CF                     cmp bx, cx
.text:0045E5D2                     jle short loc_45E5D7
.text:0045E5D4                     mov cx, bx
.text:0045E5D7
.text:0045E5D7 loc_45E5D7:                                                 ; CODE XREF:
proc_CRC_Calc_BUF_NoIgnore_Word_Zeros_S2+42j
.text:0045E5D7                     ror ecx, 10h
.text:0045E5DA                     cmp bx, cx
.text:0045E5DD                     jge short loc_45E5E2
.text:0045E5DF                     mov cx, bx
.text:0045E5E2
.text:0045E5E2 loc_45E5E2:                                                 ; CODE XREF:
proc_CRC_Calc_BUF_NoIgnore_Word_Zeros_S2+4Dj
.text:0045E5E2                     ror ecx, 10h
.text:0045E5E5                     add edi, 4
.text:0045E5E8                     sub eax, 1
.text:0045E5EB                     cmp eax, 0
.text:0045E5EE                     jge short loc_45E5AA
.text:0045E5F0                     mov [edx], ecx
.text:0045E5F2                     pop edi
.text:0045E5F3                     pop esi
.text:0045E5F4                     pop edx
.text:0045E5F5                     pop ecx
.text:0045E5F6                     pop ebx
.text:0045E5F7                     pop eax
.text:0045E5F8                     pop edi
.text:0045E5F9                     pop esi
.text:0045E5FA                     pop ebx
.text:0045E5FB                     pop ebp
.text:0045E5FC                     retn 10h
.text:0045E5FC proc_CRC_Calc_BUF_NoIgnore_Word_Zeros_S2 endp

So, please, fix this bug! Please correct the first routine
so that it begins to calculate correct values. You should
add right channel word calculation if it is nonzero.
Sorry for such a long letter and of course sorry for my
(ugly!) English (I'm just a student of a Department of Mathematics and
Mechanics of Moscow State University and forgot it at all )
I hope my explanations were correct and precise, but if not
(what's a pity!), I'll try to explain again.
Hope You'll be able to fix this. As far as I know, this
problem still persists in the latest prebeta EAC release,
so I'll be glad to see it fixed in the next release.
Sorry once again! Thank You for Your great program!
--
Best regards, DMVN