bitap algorithm in c code example

Example: Bitap Algorithm in c

/*****Please include following header files*****/
// string.h
// limits.h
/***********************************************/

int SearchString(const char *text, const char *pattern)
{
	int m = strlen(pattern);
	unsigned long R;
	unsigned long patternMask[CHAR_MAX + 1];
	int i;

	if (pattern[0] == '\0') return 0;
	if (m > 31) return -1; //Error: The pattern is too long!

	R = ~1;

	for (i = 0; i <= CHAR_MAX; ++i)
		patternMask[i] = ~0;

	for (i = 0; i < m; ++i)
		patternMask[pattern[i]] &= ~(1UL << i);

	for (i = 0; text[i] != '\0'; ++i)
	{
		R |= patternMask[text[i]];
		R <<= 1;

		if (0 == (R & (1UL << m)))
			return (i - m) + 1;
	}

	return -1;
}