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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <err.h>
static void
usage(const char *argv0)
{
fprintf(stderr, "usage: %s needle [window-size] < haystack\n", argv0);
exit(EXIT_FAILURE);
}
static const char*
search(const char *haystack, const char *needle, const size_t window_size)
{
for (const char *s = haystack; s < haystack + window_size; ++s) {
if (memcmp(s, needle, window_size))
continue;
return s;
}
return NULL;
}
static void
search_and_exit_if_match(const char *haystack, const char *needle, const size_t window_size, const size_t offset)
{
const char *match;
if ((match = search(haystack, needle, window_size))) {
printf("%zu\n", offset + match - haystack);
free((void*)needle);
free((void*)haystack);
exit(EXIT_SUCCESS);
}
}
int
main(int argc, const char *argv[])
{
size_t window_size = 4096 * 1024;
bool has_window_size = false;
if (argc < 2)
usage(argv[0]);
else if (argc > 2) {
window_size = strtoull(argv[2], NULL, 10);
has_window_size = true;
}
FILE *f;
if (!(f = fopen(argv[1], "rb")))
err(EXIT_FAILURE, "fopen(%s)", argv[1]);
if (!has_window_size) {
fseek(f, 0, SEEK_END);
const long tell = ftell(f);
window_size = (tell > 0 ? (size_t)tell : window_size);
fseek(f, 0, SEEK_SET);
}
char *needle;
if (!(needle = malloc(window_size)))
err(EXIT_FAILURE, "malloc");
window_size = fread(needle, 1, window_size, f);
fclose(f);
char *haystack;
if (!(haystack = calloc(2, window_size)))
err(EXIT_FAILURE, "calloc");
size_t rd = 0, offset = 0;
while ((rd = fread(haystack + window_size * !!offset, 1 + !offset, window_size, stdin))) {
search_and_exit_if_match(haystack, needle, (rd >= window_size ? window_size : 0), offset);
offset += window_size;
memmove(haystack, haystack + window_size, window_size);
}
search_and_exit_if_match(haystack, needle, (rd >= window_size ? window_size : 0), offset);
free(needle);
free(haystack);
return EXIT_FAILURE;
}
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