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116 lines
3.5 KiB
ArmAsm
116 lines
3.5 KiB
ArmAsm
#include <asm.inc>
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#if 0
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page ,132
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title strrev - reverse a string in place
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;***
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;strrev.asm - reverse a string in place
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;
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; Copyright (c) Microsoft Corporation. All rights reserved.
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;
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;Purpose:
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; defines _strrev() - reverse a string in place (not including
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; '\0' character)
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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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;char *_strrev(string) - reverse a string in place
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;
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;Purpose:
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; Reverses the order of characters in the string. The terminating
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; null character remains in place.
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;
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; Algorithm:
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; char *
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; _strrev (string)
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; char *string;
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; {
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; char *start = string;
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; char *left = string;
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; char ch;
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;
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; while (*string++)
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; ;
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; string -= 2;
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; while (left < string)
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; {
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; ch = *left;
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; *left++ = *string;
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; *string-- = ch;
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; }
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; return(start);
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; }
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;
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; NOTE: There is a check for an empty string in the following code.
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; Normally, this would fall out of the "cmp si,di" instruction in the
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; loop portion of the routine. However, if the offset of the empty
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; string is 0 (as it could be in large model), then the cmp does not
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; catch the empty string and the routine essentially hangs (i.e., loops
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; moving bytes one at a time FFFFh times). An explicit empty string
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; check corrects this.
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;
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;Entry:
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; char *string - string to reverse
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;
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;Exit:
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; returns string - now with reversed characters
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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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#endif
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.code
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public __strrev
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.PROC __strrev
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// Prolog. Original sources used ML's extended PROC feature to autogenerate this.
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push ebp
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mov ebp, esp
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push edi // uses edi esi
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push esi
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#define string ebp + 8 // string:ptr byte
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mov edi,[string] // di = string
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mov edx,edi // dx=pointer to string; save return value
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mov esi,edi // si=pointer to string
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xor eax,eax // search value (null)
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or ecx,-1 // cx = -1
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repne scasb // find null
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cmp ecx,-2 // is string empty? (if offset value is 0, the
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je short done // cmp below will not catch it and we'll hang).
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sub edi,2 // string is not empty, move di pointer back
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// di points to last non-null byte
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lupe:
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cmp esi,edi // see if pointers have crossed yet
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jae short done // exit when pointers meet (or cross)
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mov ah,[esi] // get front byte...
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mov al,[edi] // and end byte
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mov [esi],al // put end byte in front...
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mov [edi],ah // and front byte at end
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add esi,1 // front moves up...
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sub edi,1 // and end moves down
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jmp short lupe // keep switching bytes
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done:
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mov eax,edx // return value: string addr
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// Epilog. Original sources used ML's extended PROC feature to autogenerate this.
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pop esi
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pop edi
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pop ebp
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ret // _cdecl return
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.ENDP // __strrev
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end
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