121 lines
2.7 KiB
NASM
121 lines
2.7 KiB
NASM
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page ,132
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title strncmp - compare first n chars of two strings
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;***
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;strncmp.asm - compare first n characters of two strings
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;
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; Copyright (c) 1985-2001, Microsoft Corporation. All rights reserved.
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;
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;Purpose:
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; defines strncmp() - compare first n characters of two strings
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; for lexical order.
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;
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;Revision History:
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; 10-26-83 RN initial version
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; 05-18-88 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 386 cleanup
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; 10-26-88 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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;int strncmp(first, last, count) - compare first count chars of strings
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;
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;Purpose:
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; Compares two strings for lexical order. The comparison stops
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; after: (1) a difference between the strings is found, (2) the end
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; of the strings is reached, or (3) count characters have been
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; compared.
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;
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; Algorithm:
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; int
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; strncmp (first, last, count)
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; char *first, *last;
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; unsigned count;
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; {
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; if (!count)
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; return(0);
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; while (--count && *first && *first == *last)
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; {
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; first++;
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; last++;
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; }
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; return(*first - *last);
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; }
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;
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;Entry:
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; char *first, *last - strings to compare
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; unsigned count - maximum number of characters to compare
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;
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;Exit:
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; returns <0 if first < last
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; returns 0 if first == last
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; returns >0 if first > last
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;
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;Uses:
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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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public strncmp
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strncmp proc \
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uses edi esi ebx, \
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first:ptr byte, \
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last:ptr byte, \
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count:IWORD
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mov ecx,[count] ; cx=max number of bytes to compare
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jecxz short toend ; it's as if strings are equal
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mov ebx,ecx ; bx saves count
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mov edi,[first] ; di=first pointer (es=segment part)
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mov esi,edi ; si saves first pointer
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xor eax,eax ; ax=0
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repne scasb ; count bytes
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neg ecx ; cx=count - strlen
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add ecx,ebx ; strlen + count - strlen
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okay:
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mov edi,esi ; restore first pointer
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mov esi,[last] ; si = last pointer
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repe cmpsb ; compare strings
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mov al,[esi-1]
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xor ecx,ecx ; set return value = 0
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cmp al,[edi-1] ; last-first
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ja short lastbig ; <last is bigger>
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je short toend ; <equal>
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;jb short firstbig ; <first is bigger>
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firstbig:
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dec ecx ; first string is bigger
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dec ecx ; make FFFE so 'not' will give 0001
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lastbig: ; last string is bigger
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not ecx ; return -1
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toend:
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mov eax,ecx ; return value
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ifdef _STDCALL_
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ret 2*DPSIZE + ISIZE ; _stdcall return
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else
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ret ; _cdecl return
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endif
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strncmp endp
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end
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