libroot/string: Apply the same optimization to strncmp as in strcmp.

src/system/libroot/posix/string/strncmp.c

@@ -4,12 +4,29 @@
  */
 
 
+#include <stdint.h>
 #include <string.h>
 
 
+#define LACKS_ZERO_BYTE(value) \
+	(((value - 0x01010101) & ~value & 0x80808080) == 0)
+
 int
 strncmp(char const *a, char const *b, size_t count)
 {
+	if ((((addr_t)a) & 3) == 0 && (((addr_t)b) & 3) == 0) {
+		uint32_t *a32 = (uint32_t *)a;
+		uint32_t *b32 = (uint32_t *)b;
+
+		while (count >= 4 && *a32 == *b32 && LACKS_ZERO_BYTE((*a32))) {
+			a32++;
+			b32++;
+			count -= 4;
+		}
+		a = (const char *)a32;
+		b = (const char *)b32;
+	}
+
 	while (count-- > 0) {
 		int cmp = (unsigned char)*a - (unsigned char)*b++;
 		if (cmp != 0 || *a++ == '\0')