ref: 608b648f64d54375da8700e82d217b7c3e2e3d03
dir: /sys/src/ape/lib/bsd/strncasecmp.c/
#include <string.h>
typedef unsigned char uchar;
int
strncasecmp(char *s1, char *s2, int n)
{
	int c1, c2;
	while(*s1 && n-- > 0){
		c1 = *(uchar*)s1++;
		c2 = *(uchar*)s2++;
		if(c1 == c2)
			continue;
		if(c1 >= 'A' && c1 <= 'Z')
			c1 -= 'A' - 'a';
		if(c2 >= 'A' && c2 <= 'Z')
			c2 -= 'A' - 'a';
		if(c1 != c2)
			return c1 - c2;
	}
	if(n <= 0)
		return 0;
	return -*s2;
}