An implementation of strcmp()

string_compare.c

// https://godbolt.org/g/56Lv4f  - 62 opcodes
int strcmp_original(char *a, char *b)
{
	int c = strlen(a) > strlen(b) ? strlen(a) : strlen(b);
	char * d;

	for (d = a;d < a + c;++d, ++b)
	{
		if (*d != *b)
		{
			return (*d - *b);
		}
	}
	return 0;
}
 
// 56 opcodes (39 lines with -O2)
int strcmp_better(char *a, char *b)
{
	int len_a = strlen(a);
	int len_b = strlen(b);
	int len_max = len_a > len_b ? len_a : len_b;
	char *p;
	for (p = a;p < (a + len_max);++p, ++b)
	{
		if (*p != *b)
		{
			return (*p - *b);
		}
	}
	return 0;
}

// 30 opcodes (19 lines with -O2)
int strcmp_refactored(const char *s1, const char *s2)
{
	while ((*s1 != 0) && (*s1 == *s2))
	{
		++s1;
		++s2;
	}
	return (*s1 - *s2);
}

// 15 opcodes with -O2 
int strcmp_refactored_2(const char *s1, const char *s2)
{
	while (1)
	{
		int res = ((*s1 == 0) || (*s1 != *s2));
		if  (__builtin_expect((res),0))
		{
			break;
		}
		++s1;
		++s2;
	}
	return (*s1 - *s2);
}