我正在尝试在Linux上编写一个尽可能快的crc32实现,以便练习优化C语言的能力。我已经尽力了,但是在网上找不到很好的资源。我甚至不确定我的缓冲区大小是否合理,因为这是通过反复试验选择的。
#include <stdio.h>
#define BUFFSIZE 1048567
const unsigned long int lookupbase = 0xEDB88320;
unsigned long int crctable[256] = {
0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA,
/* LONG LIST OF PRECALCULTED VALUES */
0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D};
int main(int argc, char *argv[]){
register unsigned long int x;
int i;
register unsigned char *c, *endbuff;
unsigned char buff[BUFFSIZE];
register FILE *thisfile=NULL;
for (i = 1; i < argc; i++){
thisfile = fopen(argv[i], "r");
if (thisfile == NULL) {
printf("Unable to open ");
} else {
x = 0xFFFFFFFF;
c = &(buff[0]);
endbuff = &(buff[fread(buff, (sizeof (unsigned char)), BUFFSIZE, thisfile)]);
while (c != endbuff){
while (c != endbuff){
x=(x>>8) ^ crctable[(x&0xFF)^*c];
c++;
}
c = &(buff[0]);
endbuff = &(buff[fread(buff, (sizeof (unsigned char)), BUFFSIZE, thisfile)]);
}
fclose(thisfile);
x = x ^ 0xFFFFFFFF;
printf("%0.8X ", x);
}
printf("%s\n", argv[i]);
}
return 0;
}
非常感谢您提供的任何建议或资源,我可以仔细阅读。
x =(x >> 8)^ crctable [(x&0xFF)^ * c];
更改为x ^ = * c
可以将我的PC上的运行时间减半。 - sockmeistr