105 lines
2.6 KiB
NASM
105 lines
2.6 KiB
NASM
page ,132
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title strcmp.asm - compare two strings
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;***
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;strcmp.asm - routine to compare two strings (for equal, less, or greater)
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;
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; Copyright (c) 1985-1991, Microsoft Corporation. All rights reserved.
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;
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;Purpose:
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; STRCMP compares two strings and returns an integer
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; to indicate whether the first is less than the second, the two are
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; equal, or whether the first is greater than the second, respectively.
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; Comparison is done byte by byte on an UNSIGNED basis, which is to
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; say that Null (0) is less than any other character (1-255).
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;
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;Revision History:
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; 04-21-87 SKS Module rewritten to be fast and small
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; 05-17-88 SJM Add model-independent (large model) ifdef
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; 08-04-88 SJM convert to cruntime/ add 32-bit support
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; 08-23-88 JCR Minor 386 cleanup
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; 10-25-88 JCR General cleanup for 386-only code
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; 03-23-90 GJF Changed to _stdcall. Also, fixed the copyright.
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; 05-10-91 GJF Back to _cdecl, sigh...
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;
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;*******************************************************************************
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.xlist
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include cruntime.inc
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.list
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page
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;***
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;strcmp - compare two strings, returning less than, equal to, or greater than
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;
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;Purpose:
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; Compares two string, determining their lexical order. Unsigned
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; comparison is used.
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;
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; Algorithm:
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; int strcmp ( src , dst )
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; unsigned char *src;
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; unsigned char *dst;
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; {
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; int ret = 0 ;
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;
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; while( ! (ret = *src - *dst) && *dst)
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; ++src, ++dst;
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;
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; if ( ret < 0 )
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; ret = -1 ;
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; else if ( ret > 0 )
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; ret = 1 ;
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;
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; return( ret );
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; }
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;
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;Entry:
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; const char * src - string for left-hand side of comparison
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; const char * dst - string for right-hand side of comparison
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;
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;Exit:
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; AX < 0, 0, or >0, indicating whether the first string is
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; Less than, Equal to, or Greater than the second string.
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;
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;Uses:
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; CX, DX
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;
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;Exceptions:
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;
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;*******************************************************************************
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CODESEG
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.lall
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public strcmp
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strcmp proc \
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uses edi esi, \
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src:ptr byte, \
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dst:ptr byte
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mov esi,[src] ; si = source
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xor eax,eax ; mingle register instr with mem instr.
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mov edi,[dst] ; di = dest
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or ecx,-1 ; cx = -1
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repne scasb ; compute length of "dst"
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not ecx ; CX = strlen(dst)+1
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sub edi,ecx ; restore DI = dst
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repe cmpsb ; compare while equal, at most length of "dst"
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je short toend ; dst == src? (AX = 0)
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; dst < src dst > src
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sbb eax,eax ; AX=-1, CY=1 AX=0, CY=0
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sbb eax,-1 ; AX=-1 AX=1
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toend:
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ifdef _STDCALL_
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ret 2*DPSIZE ; _stdcall return
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else
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ret ; _cdecl return
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endif
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strcmp endp
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end
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