breakhack/checksum/src/checksum.c

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/*
** CHECKSUM.C - Compute the checksum of a file
**
** public somain demo by Bob Stout
*/
#include <stdlib.h>
#include "checksum.h"
unsigned
checksum(void *buffer, size_t len, unsigned int seed)
{
unsigned char *buf = (unsigned char *)buffer;
size_t i;
for (i = 0; i < len; ++i)
seed += (unsigned int)(*buf++);
return seed;
}
unsigned
checksum_fp(FILE *fp)
{
unsigned int seed = 0;
char buf[4096];
size_t len;
do {
len = fread(buf, sizeof(char), sizeof(buf), fp);
seed = checksum(buf, len, seed);
} while (len > 0);
return seed;
}
#ifdef EXECUTABLE
#include <stdio.h>
int main(int argc, char *argv[])
{
FILE *fp;
const char *file;
if (argc < 2) {
printf("You need to provide an input file\n");
printf("Example: %s <file>", argv[0]);
}
file = argv[1];
if (NULL == (fp = fopen(file, "rb")))
{
printf("Unable to open %s for reading\n", file);
return -1;
}
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printf("%#x\n", checksum_fp(fp));
return 0;
}
#endif