mailing list of musl libc

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 #include <string.h>
#include <stdint.h>

#define aliases __attribute__((__may_alias__))
#define byte_repeat(x) ((size_t)~0 / 0xff * (x))
#define word_has_zero(x) (((x) - byte_repeat(0x01)) & ~(x) & byte_repeat(0x80))

size_t strlen(const char *s)
{
	const char *const s0 = s;
	const size_t aliases *ws;

	for (; (uintptr_t)s & sizeof(size_t) - 1 && *s; s++);
	if (!*s) return s - s0;

	ws = (const void *)s;
	for (; !word_has_zero(*ws); ws++);
	s = (const void *)ws;

	for (; *s; s++);

	return s - s0;
}