1 files changed, 84 insertions, 0 deletions
diff --git a/binsearch.c b/binsearch.c
new file mode 100644
index 0000000..a4195ba
--- /dev/null
+++ b/binsearch.c
@@ -0,0 +1,84 @@
+#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[])
+{
+   // default incase failure, or cant get size of file
+   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;
+}