122 lines
4.1 KiB
C
122 lines
4.1 KiB
C
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/****************************************************************************
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*
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* Open Watcom Project
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*
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* Portions Copyright (c) 1983-2002 Sybase, Inc. All Rights Reserved.
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*
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* ========================================================================
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*
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* This file contains Original Code and/or Modifications of Original
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* Code as defined in and that are subject to the Sybase Open Watcom
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* Public License version 1.0 (the 'License'). You may not use this file
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* except in compliance with the License. BY USING THIS FILE YOU AGREE TO
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* ALL TERMS AND CONDITIONS OF THE LICENSE. A copy of the License is
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* provided with the Original Code and Modifications, and is also
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* available at www.sybase.com/developer/opensource.
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*
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* The Original Code and all software distributed under the License are
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* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
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* EXPRESS OR IMPLIED, AND SYBASE AND ALL CONTRIBUTORS HEREBY DISCLAIM
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* ALL SUCH WARRANTIES, INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR
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* NON-INFRINGEMENT. Please see the License for the specific language
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* governing rights and limitations under the License.
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*
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* ========================================================================
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*
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* Description: WHEN YOU FIGURE OUT WHAT THIS FILE DOES, PLEASE
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* DESCRIBE IT HERE!
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*
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****************************************************************************/
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#include "variety.h"
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#include <ctype.h>
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#include <string.h>
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#ifdef M_I86
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/*
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explanation of algorithm:
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(1) reverse as much of the string as possible as words
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(2) after main loop: reverse residual inner string (0-3 bytes)
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the string falls into one of these forms:
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{ prefix_word }* { suffix_word }*
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{ prefix_word }* middle_byte { suffix_word }*
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{ prefix_word }* pre_middle_byte post_middle_byte { suffix_word }*
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{ prefix_word }* pre_middle_byte middle_byte post_middle_byte { suffix_word }*
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we only have to swap two bytes when:
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len & 2 != 0 is true (ie. the carry is set after second shr cx,1)
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*****************************************************************************
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WARNING: the code in the L1: ... reverse loop cannot modify the carry flag
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*****************************************************************************
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*/
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extern void fast_rev( char _WCFAR * );
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#pragma aux fast_rev = \
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0x1e /* push ds */\
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0x8e 0xc1 /* mov es,cx */\
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0x8e 0xd9 /* mov ds,cx */\
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0x89 0xfe /* mov si,di */\
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0xb9 0xff 0xff /* mov cx,ffff */\
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0x30 0xc0 /* xor al,al */\
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0xf2 0xae /* repne scasb */\
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0xf7 0xd1 /* not cx */\
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0x49 /* dec cx */\
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0xfd /* std */\
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0x83 0xef 0x03 /* sub di,3 */\
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0xd1 0xe9 /* shr cx,1 */\
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0xd1 0xe9 /* shr cx,1 */\
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0xe3 0x0d /* jcxz L2 */\
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0x8b 0x05 /* L1:mov ax,[di] */\
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0x86 0xe0 /* xchg ah,al */\
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0x87 0x04 /* xchg ax,[si] */\
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0x86 0xe0 /* xchg ah,al */\
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0xab /* stosw */\
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0x46 /* inc si */\
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0x46 /* inc si */\
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0xe2 0xf3 /* loop L1 */\
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0x73 0x07 /* L2:jnc L3 */\
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0x47 /* inc di */\
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0x8a 0x05 /* mov al,[di] */\
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0x86 0x04 /* xchg al,[si] */\
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0x88 0x05 /* mov [di],al */\
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0xfc /* L3:cld */\
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0x1f /* pop ds */\
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parm caller [cx di] \
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modify [si cx ax di es];
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#endif
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_WCRTLINK char _WCFAR *_fstrrev( char _WCFAR *str ) /* reverse characters in string */
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{
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#if defined(M_I86)
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fast_rev( str );
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return( str );
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#else
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char _WCFAR *p1;
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char _WCFAR *p2;
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char c1;
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char c2;
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p1 = str;
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p2 = p1 + _fstrlen( p1 ) - 1;
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while( p1 < p2 ) {
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c1 = *p1;
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c2 = *p2;
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*p1 = c2;
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*p2 = c1;
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++p1;
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--p2;
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}
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return( str );
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#endif
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}
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