add a (inefficient) rawmemchr implementation

libc/build.mak

@@ -493,6 +493,7 @@ libc += string/memmove.o
 libc += string/mempcpy.o
 libc += string/memrchr.o
 libc += string/memset.o
+libc += string/rawmemchr.o
 libc += string/rindex.o
 libc += string/stpcpy.o
 libc += string/stpncpy.o

libc/string/rawmemchr.c

+#include <string.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <limits.h>
+#include "libc.h"
+
+#define SS (sizeof(size_t))
+#define ALIGN (sizeof(size_t)-1)
+#define ONES ((size_t)-1/UCHAR_MAX)
+#define HIGHS (ONES * (UCHAR_MAX/2+1))
+#define HASZERO(x) (((x)-ONES) & ~(x) & HIGHS)
+
+void *__rawmemchr(const void *src, int c)
+{
+	long n = LONG_MAX;
+	const unsigned char *s = src;
+	c = (unsigned char)c;
+	for (; ((uintptr_t)s & ALIGN) && n && *s != c; s++, n--);
+	if (n && *s != c) {
+		const size_t *w;
+		size_t k = ONES * c;
+		for (w = (const void *)s; n>=SS && !HASZERO(*w^k); w++, n-=SS);
+		for (s = (const void *)w; n && *s != c; s++, n--);
+	}
+	return n ? (void *)s : 0;
+}
+weak_alias(__rawmemchr, rawmemchr);