Boyer-Moore String Search

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static int calc_skip(char *);
static int faster_match(char *, char *, int);

#define CHARS 128
static int skip[CHARS];

int main(void) {
  char *text = "XYXZde0XZZkWXYZ";
  char *pattern = "WXYZ";
  int n = strlen(text);
  int ret = faster_match(text, pattern, n);
  if (ret < 0) {
    exit(1);
  }
  printf("%d\n", ret);
  printf("%s\n", text + ret);
}

static int calc_skip(char *pattern) {
  int i, m;
  m = strlen(pattern);
  for (i = 0; i < CHARS; ++i) {
    skip[i] = m;
  }
  for (i = 0; i < m; ++i) {
    skip[(int) pattern[i]] = m - i - 1;
  }
  return m;
}

static int faster_match(char *text, char *pattern, int n) {
  int m = calc_skip(pattern) - 1;
  int i = m, j;
  while (i < n) {
    j = m;
    while (j >= 0) {
      if (text[i] == pattern[j]) {
        if (j == 0) {
          return i;
        }
        --i, --j;
      } else {
        break;
      }
    }
    i += (skip[(int) text[i]] > m - j ? skip[(int) text[i]] : m - j + 1);
  }
  return -1;
}