strncasecmp.c\string\src - musl - musl - an implementation of the standard library for Linux-based systems

#include <strings.h>
#include <ctype.h>
int strncasecmp(const char *_l, const char *_r, size_t n)
{
	const unsigned char *l=(void *)_l, *r=(void *)_r;
	if (!n--) return 0;
	for (; *l && *r && n && (*l == *r || tolower(*l) == tolower(*r)); l++, r++, n--);
	return tolower(*l) - tolower(*r);
}