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Diffstat (limited to 'private/crt32/string/i386/strrev.asm')
| -rw-r--r-- | private/crt32/string/i386/strrev.asm | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/private/crt32/string/i386/strrev.asm b/private/crt32/string/i386/strrev.asm new file mode 100644 index 000000000..09071834e --- /dev/null +++ b/private/crt32/string/i386/strrev.asm @@ -0,0 +1,121 @@ + page ,132 + title strrev - reverse a string in place +;*** +;strrev.asm - reverse a string in place +; +; Copyright (c) 1985-1991, Microsoft Corporation. All rights reserved. +; +;Purpose: +; defines _strrev() - reverse a string in place (not including +; '\0' character) +; +;Revision History: +; 10-26-83 RN initial version +; 07-16-87 JCR Added check for empty string (fixes large model bug) +; 05-18-88 SJM Add model-independent (large model) ifdef +; 08-04-88 SJM convert to cruntime/ add 32-bit support +; 08-23-88 JCR 386 cleanup, minor alterations +; 10-26-88 JCR General cleanup for 386-only code +; 10-26-88 JCR Re-arrange regs to avoid push/pop ebx +; 03-26-90 GJF Changed to _stdcall. Also, fixed the copyright. +; 01-18-91 GJF ANSI naming. +; 05-10-91 GJF Back to _cdecl, sigh... +; +;******************************************************************************* + + .xlist + include cruntime.inc + .list + +page +;*** +;char *_strrev(string) - reverse a string in place +; +;Purpose: +; Reverses the order of characters in the string. The terminating +; null character remains in place. +; +; Algorithm: +; char * +; _strrev (string) +; char *string; +; { +; char *start = string; +; char *left = string; +; char ch; +; +; while (*string++) +; ; +; string -= 2; +; while (left < string) +; { +; ch = *left; +; *left++ = *string; +; *string-- = ch; +; } +; return(start); +; } +; +; NOTE: There is a check for an empty string in the following code. +; Normally, this would fall out of the "cmp si,di" instruction in the +; loop portion of the routine. However, if the offset of the empty +; string is 0 (as it could be in large model), then the cmp does not +; catch the empty string and the routine essentially hangs (i.e., loops +; moving bytes one at a time FFFFh times). An explicit empty string +; check corrects this. +; +;Entry: +; char *string - string to reverse +; +;Exit: +; returns string - now with reversed characters +; +;Uses: +; +;Exceptions: +; +;******************************************************************************* + + CODESEG + + public _strrev +_strrev proc \ + uses edi esi, \ + string:ptr byte + + mov edi,[string] ; di = string + mov edx,edi ; dx=pointer to string; save return value + + mov esi,edi ; si=pointer to string + xor eax,eax ; search value (null) + or ecx,-1 ; cx = -1 +repne scasb ; find null + cmp ecx,-2 ; is string empty? (if offset value is 0, the + je short done ; cmp below will not catch it and we'll hang). + + dec edi ; string is not empty, move di pointer back + dec edi ; di points to last non-null byte + +lupe: + cmp esi,edi ; see if pointers have crossed yet + jae short done ; exit when pointers meet (or cross) + + mov ah,[esi] ; get front byte... + mov al,[edi] ; and end byte + mov [esi],al ; put end byte in front... + mov [edi],ah ; and front byte at end + inc esi ; front moves up... + dec edi ; and end moves down + jmp short lupe ; keep switching bytes + +done: + mov eax,edx ; return value: string addr + +ifdef _STDCALL_ + ret DPSIZE ; _stdcall return +else + ret ; _cdecl return +endif + +_strrev endp + end |