157 lines
4.9 KiB
NASM
157 lines
4.9 KiB
NASM
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; crc_i386.asm, optimized CRC calculation function for Zip and UnZip, not
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; copyrighted by Paul Kienitz and Christian Spieler. Last revised 10 Nov 96.
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;
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; Revised 06-Oct-96, Scott Field (sfield@microsoft.com)
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; fixed to assemble with masm by not using .model directive which makes
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; assumptions about segment alignment. Also,
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; avoid using loop, and j[e]cxz where possible. Use mov + inc, rather
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; than lodsb, and other misc. changes resulting in the following performance
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; increases:
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;
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; unrolled loops NO_UNROLLED_LOOPS
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; *8 >8 <8 *8 >8 <8
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;
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; +54% +42% +35% +82% +52% +25%
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;
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; first item in each table is input buffer length, even multiple of 8
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; second item in each table is input buffer length, > 8
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; third item in each table is input buffer length, < 8
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;
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;
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; FLAT memory model assumed.
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;
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; The loop unroolling can be disabled by defining the macro NO_UNROLLED_LOOPS.
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; This results in shorter code at the expense of reduced performance.
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;
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;==============================================================================
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;
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; Do NOT assemble this source if external crc32 routine from zlib gets used.
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;
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IFNDEF USE_ZLIB
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;
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.386p
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name crc_i386
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; don't make assumptions about segment align .model flat
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extrn _get_crc_table:near ; ulg near *get_crc_table(void);
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;
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IFNDEF NO_STD_STACKFRAME
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; Use a `standard' stack frame setup on routine entry and exit.
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; Actually, this option is set as default, because it results
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; in smaller code !!
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STD_ENTRY MACRO
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push ebp
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mov ebp,esp
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ENDM
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Arg1 EQU 08H[ebp]
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Arg2 EQU 0CH[ebp]
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Arg3 EQU 10H[ebp]
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STD_LEAVE MACRO
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pop ebp
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ENDM
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ELSE ; NO_STD_STACKFRAME
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STD_ENTRY MACRO
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ENDM
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Arg1 EQU 18H[esp]
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Arg2 EQU 1CH[esp]
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Arg3 EQU 20H[esp]
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STD_LEAVE MACRO
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ENDM
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ENDIF ; ?NO_STD_STACKFRAME
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; This is the loop body of the CRC32 cruncher.
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; registers modified:
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; ebx : crc value "c"
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; esi : pointer to next data byte "buf++"
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; registers read:
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; edi : pointer to base of crc_table array
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; scratch registers:
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; eax : requires upper three bytes of eax = 0, uses al
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Do_CRC MACRO
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mov al, byte ptr [esi] ; al <-- *buf
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inc esi ; buf++
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xor al,bl ; (c ^ *buf++) & 0xFF
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shr ebx,8 ; c = (c >> 8)
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xor ebx,[edi+eax*4] ; ^ table[(c ^ *buf++) & 0xFF]
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ENDM
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_TEXT segment para
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public _crc32
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_crc32 proc near ; ulg crc32(ulg crc, ZCONST uch *buf, extent len)
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STD_ENTRY
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push edi
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push esi
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push ebx
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push edx
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push ecx
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mov esi,Arg2 ; 2nd arg: uch *buf
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sub eax,eax ;> if (!buf)
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test esi,esi ;> return 0;
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jz fine ;> else {
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call _get_crc_table
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mov edi,eax
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mov ebx,Arg1 ; 1st arg: ulg crc
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sub eax,eax ; eax=0; make al usable as a dword
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mov ecx,Arg3 ; 3rd arg: extent len
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not ebx ;> c = ~crc;
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IFNDEF NO_UNROLLED_LOOPS
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mov edx,ecx ; save len in edx
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and edx,000000007H ; edx = len % 8
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shr ecx,3 ; ecx = len / 8
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jz No_Eights
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; align loop head at start of 486 internal cache line !!
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align 16
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Next_Eight:
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Do_CRC
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Do_CRC
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Do_CRC
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Do_CRC
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Do_CRC
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Do_CRC
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Do_CRC
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Do_CRC
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dec ecx
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jnz Next_Eight
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No_Eights:
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mov ecx,edx
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ENDIF ; NO_UNROLLED_LOOPS
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jecxz bail ;> if (len)
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; align loop head at start of 486 internal cache line !!
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align 16
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loupe: ;> do {
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Do_CRC ; c = CRC32(c, *buf++);
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dec ecx ;> } while (--len);
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jnz loupe
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bail: ;> }
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mov eax,ebx
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not eax ;> return ~c;
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fine:
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pop ecx
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pop edx
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pop ebx
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pop esi
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pop edi
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STD_LEAVE
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ret
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_crc32 endp
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_TEXT ends
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;
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ENDIF ;!USE_ZLIB
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;
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end
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