page ,132 title strncat - append n chars of string1 to string2 ;*** ;strncat.asm - append n chars of string to new string ; ; Copyright (c) 1985-2001, Microsoft Corporation. All rights reserved. ; ;Purpose: ; defines strncat() - appends n characters of string onto ; end of other string ; ;Revision History: ; 10-25-83 RN initial version ; 08-05-87 SKS Fixed bug: extra null was stored if n > strlen(back) ; 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 Minor 386 cleanup ; 10-26-88 JCR General cleanup for 386-only code ; 03-23-90 GJF Changed to _stdcall. Also, fixed the copyright. ; 05-10-91 GJF Back to _cdecl, sigh... ; 12-15-96 GJF Faster version from Intel. ; 12-19-96 GJF Fixed bugs in Intel code ; ;******************************************************************************* .xlist include cruntime.inc .list page ;*** ;char *strncat(front, back, count) - append count chars of back onto front ; ;Purpose: ; Appends at most count characters of the string back onto the ; end of front, and ALWAYS terminates with a null character. ; If count is greater than the length of back, the length of back ; is used instead. (Unlike strncpy, this routine does not pad out ; to count characters). ; ; Algorithm: ; char * ; strncat (front, back, count) ; char *front, *back; ; unsigned count; ; { ; char *start = front; ; ; while (*front++) ; ; ; front--; ; while (count--) ; if (!(*front++ = *back++)) ; return(start); ; *front = '\0'; ; return(start); ; } ; ;Entry: ; char * front - string to append onto ; char * back - string to append ; unsigned count - count of max characters to append ; ;Exit: ; returns a pointer to string appended onto (front). ; ;Uses: ECX, EDX ; ;Exceptions: ; ;******************************************************************************* CODESEG public strncat strncat proc ; front:ptr byte, ; back:ptr byte, ; count:IWORD .FPO ( 0, 3, 0, 0, 0, 0 ) mov ecx,[esp + 0ch] ; ecx = count push edi ; preserve edi test ecx,ecx jz finish ; leave if count is zero mov edi,[esp + 8] ; edi -> front string push esi ; preserve esi test edi,3 ; is string aligned on dword (4 bytes) push ebx ; preserve ebx je short find_end_of_front_string_loop ; simple byte loop until string is aligned front_misaligned: mov al,byte ptr [edi] inc edi test al,al je short start_byte_3 test edi,3 jne short front_misaligned find_end_of_front_string_loop: mov eax,dword ptr [edi] ; read dword (4 bytes) mov edx,7efefeffh add edx,eax xor eax,-1 xor eax,edx add edi,4 test eax,81010100h je short find_end_of_front_string_loop ; found zero byte in the loop mov eax,[edi - 4] test al,al ; is it byte 0 je short start_byte_0 test ah,ah ; is it byte 1 je short start_byte_1 test eax,00ff0000h ; is it byte 2 je short start_byte_2 test eax,0ff000000h ; is it byte 3 jne short find_end_of_front_string_loop ; taken if bits 24-30 are clear and bit ; 31 is set start_byte_3: dec edi jmp short copy_start start_byte_2: sub edi,2 jmp short copy_start start_byte_1: sub edi,3 jmp short copy_start start_byte_0: sub edi,4 ; edi now points to the end of front string. copy_start: mov esi,[esp + 14h] ; esi -> back string test esi,3 ; is back string is dword aligned? jnz back_misaligned mov ebx,ecx ; store count for tail loop shr ecx,2 jnz short main_loop_entrance jmp short tail_loop_start ; 0 < counter < 4 ; simple byte loop until back string is aligned back_misaligned: mov dl,byte ptr [esi] inc esi test dl,dl je short byte_0 mov [edi],dl inc edi dec ecx jz empty_counter test esi,3 jne short back_misaligned mov ebx,ecx ; store count for tail loop shr ecx,2 ; convert ecx to dword count jnz short main_loop_entrance tail_loop_start: mov ecx,ebx and ecx,3 ; ecx = count of leftover bytes after the ; dwords have been concatenated jz empty_counter tail_loop: mov dl,byte ptr [esi] inc esi mov [edi],dl inc edi test dl,dl je short finish1 ; '\0' was already copied dec ecx jnz tail_loop empty_counter: mov [edi],cl ; cl=0; finish1: pop ebx pop esi finish: mov eax,[esp + 8] ; return in eax pointer to front string pop edi ret ; _cdecl return byte_0: mov [edi],dl mov eax,[esp + 10h] ; return in eax pointer to front string pop ebx pop esi pop edi ret ; _cdecl return main_loop: ; edx contains first dword of back string mov [edi],edx ; store one more dword add edi,4 ; kick pointer to front string dec ecx jz tail_loop_start main_loop_entrance: mov edx,7efefeffh mov eax,dword ptr [esi] ; read 4 bytes add edx,eax xor eax,-1 xor eax,edx mov edx,[esi] ; it's in cache now add esi,4 ; kick pointer to back string test eax,81010100h je short main_loop ; may be found zero byte in the loop test dl,dl ; is it byte 0 je short byte_0 test dh,dh ; is it byte 1 je short byte_1 test edx,00ff0000h ; is it byte 2 je short byte_2 test edx,0ff000000h ; is it byte 3 jne short main_loop ; taken if bits 24-30 are clear and bit ; 31 is set byte_3: mov [edi],edx mov eax,[esp + 10h] ; return in eax pointer to front string pop ebx pop esi pop edi ret ; _cdecl return byte_2: mov [edi],dx xor edx,edx mov eax,[esp + 10h] ; return in eax pointer to front string mov [edi + 2],dl pop ebx pop esi pop edi ret ; _cdecl return byte_1: mov [edi],dx mov eax,[esp + 10h] ; return in eax pointer to front string pop ebx pop esi pop edi ret ; _cdecl return strncat endp end