main.cpp
#include <stdio.h> #include <string.h> #include <malloc.h> #include <stdlib.h> extern "C" int SseTextStringReplaceChar(char* s, char old_char, char new_char); char* TestStrings[] = { (char*)("*Red*Green*Blue*"), (char*)("Cyan*Magenta Yellow*Black Tan"), (char*)("White*Pink Brown Purple*Gray Orange*"), (char*)("Beige Silver Indigo Fuchsia Maroon"), (char*)("***************"), (char*)("*****+*****+*****+*****+*****"), (char*)("") }; const char OldChar = '*'; const char NewChar = '#'; const int OffsetMin = 4096 - 40; const int OffsetMax = 4096 + 40; const int NumTestStrings = sizeof(TestStrings) / sizeof (char*); const unsigned int CheckNum = 0x12345678; int SseTextStringReplaceCharCpp(char* s, char old_char, char new_char) { char c; int n = 0; while ((c = *s) != '\0') { if (c == OldChar) { *s = NewChar; n++; } s++; } return n; } void SseTextStringReplace(void) { const int buff_size = 8192; const int page_size = 4096; char* buff1 = (char*)aligned_alloc(buff_size, page_size); char* buff2 = (char*)aligned_alloc(buff_size, page_size); printf("\nResults for SseTextStringReplaceChars()\n"); printf("OldChar = '%c' NewChar = '%c'\n", OldChar, NewChar); for (int i = 0; i < NumTestStrings; i++) { char* s = TestStrings[i]; int s_len = strlen(s); for (int offset = OffsetMin; offset <= OffsetMax; offset++) { bool print = (offset == OffsetMin) ? true : false; char* s1 = buff1 + offset; char* s2 = buff2 + offset; int size = buff_size - offset; int n1 = -1, n2 = -1; //strcpy_s(s1, size, s); strncpy(s1, s, size); *(s1 + s_len + 1) = OldChar; *((unsigned int*)(s1 + s_len + 2)) = CheckNum; //strcpy_s(s2, size, s); strncpy(s2, s, size); *(s2 + s_len + 1) = OldChar; *((unsigned int*)(s2 + s_len + 2)) = CheckNum; if (print) printf("\ns1 before replace: \"%s\"\n", s1); n1 = SseTextStringReplaceCharCpp(s1, OldChar, NewChar); if (print) printf("s1 after replace: \"%s\"\n", s1); if (print) printf("\ns2 before replace: \"%s\"\n", s2); n2 = SseTextStringReplaceChar(s2, OldChar, NewChar); if (print) printf("s2 after replace: \"%s\"\n", s2); if (strcmp(s1, s1) != 0) printf("Error - string compare failed\n"); if (n1 != n2) printf("Error - character count compare failed\n"); if (*(s1 + s_len + 1) != OldChar) printf("Error - buff1 OldChar overwrite\n"); if (*(s2 + s_len + 1) != OldChar) printf("Error - buff2 OldChar overwrite\n"); if (*((unsigned int*)(s1 + s_len + 2)) != CheckNum) printf("Error - buff1 CheckNum overwrite\n"); if (*((unsigned int*)(s2 + s_len + 2)) != CheckNum) printf("Error - buff2 CheckNum overwrite\n"); } } free(((void**)buff1)[0]); free(((void**)buff2)[0]); // free(buff1); // free(buff2); } int main(int argc, char* argv[]) { SseTextStringReplace(); return 0; }
ssetextstringreplacechar.asm
; Name: ssetextstringreplacechar.asm ; ; Build: gg++ -c -m32 main.cpp -o main.o ; nasm -f elf32 -o ssetextstringreplacechar.o ssetextstringreplacechar.asm ; g++ -m32 -o ssetextstringreplacechar ssetextstringreplacechar.o main.o ; ; Source: Modern x86 Assembly Language Programming p. 316 global SseTextStringReplaceChar section .data align 16 PxorNotMask: times 16 db 0xff ;pxor logical not mask section .text ; extern "C" int SseTextStringReplaceChar_(char* s, char old_char, char new_char); ; ; Description: The following function replaces all instances of old_char ; with new_char in the provided text string. ; ; Requires SSE4.2 and POPCNT feature flag. %define s [ebp+8] %define old_char [ebp+12] %define new_char [ebp+16] SseTextStringReplaceChar: push ebp mov ebp,esp push ebx push esi push edi ; Initialize mov eax,s ;eax = 's' sub eax,16 ;adjust eax for loop below xor edi,edi ;edi = num replaced chars ; Build packed old_char and new_char movzx ecx,byte old_char movd xmm1,ecx ;xmm1[7:0] = old_char movzx ecx,byte new_char ;ecx = new char movd xmm6,ecx pxor xmm5,xmm5 pshufb xmm6,xmm5 ;xmm6 = packed new_char movdqa xmm7,[PxorNotMask] ;xmm7 = pxor not mask ; Calculate next string address and test for near end-of-page condition .loop1: add eax,16 ;eax = next text block mov edx,eax and edx,0fffh ;edx = low 12 bits of address cmp edx,0ff0h ja .nearEndOfPage ;jump if within 16 bytes of page boundary ; Compare current text block to find characters movdqu xmm2,[eax] ;load next text block pcmpistrm xmm1,xmm2,40h ;test for old_char match setz cl ;set if '\0' found jc .foundMatch1 ;jump if matches found jz .done ;jump if '\0' found jmp .loop1 ;jump if no matches found ; Character matches found (xmm0 = match mask) ; Update character match count in EDI .foundMatch1: pmovmskb edx,xmm0 ;edx = match mask popcnt edx,edx ;count the number of matches add edi,edx ;edi = total match count ; Replace all old_char with new_char movdqa xmm3,xmm0 ;xmm3 = match mask pxor xmm0,xmm7 pand xmm0,xmm2 ;remove old_chars pand xmm3,xmm6 por xmm0,xmm3 ;insert new_chars movdqu [eax],xmm0 ;save updated string or cl,cl ;does current block contain '\0'? jnz .done ;jump if yes jmp .loop1 ;continue processing text string ; Replace old_char with new_char near end of page .nearEndOfPage: mov ecx,4096 ;size of page in bytes sub ecx,edx ;ecx = number of bytes to check mov dl,[ebp+12] ;dl = old_char mov dh,[ebp+16] ;dh = new_char .loop2: mov bl,[eax] ;load next input string character or bl,bl jz .done ;jump if '\0' found cmp dl,bl jne .@1 ;jump if no match mov [eax],dh ;replace old_char with new_char inc edi ;update num replaced characters .@1: inc eax ;eax = ptr to next char dec ecx jnz .loop2 ;repeat until end of page sub eax,16 ;adjust eax to eliminate jump ; Process remainder of text string; note that movdqa can now be used .loop3: add eax,16 ;eax = next text block movdqa xmm2,[eax] ;load next text block pcmpistrm xmm1,xmm2,40h ;test for old_char match setz cl ;set if '\0' found jc .foundMatch3 ;jump if matches found jz .done ;jump if '\0' found jmp .loop3 ;jump if no matches found .foundMatch3: pmovmskb edx,xmm0 ;edx = match mask popcnt edx,edx ;count the number of matches add edi,edx ;edi = total match count ; Replace all old_char with new_char movdqa xmm3,xmm0 ;xmm3 = match mask pxor xmm0,xmm7 pand xmm0,xmm2 ;mask out all old_chars pand xmm3,xmm6 por xmm0,xmm3 ;insert new_chars movdqa [eax],xmm0 ;save updated string or cl,cl ;does current block contain '\0'? jnz .done ;jump if yes jmp .loop3 ;continue processing text string .done: mov eax,edi ;eax = num replaced characters pop edi pop esi pop ebx pop ebp ret
build
g++ -c -m32 main.cpp -o main.o nasm -f elf32 -o ssetextstringreplacechar.o ssetextstringreplacechar.asm g++ -m32 -o ssetextstringreplacechar ssetextstringreplacechar.o main.o