/* Copyright (c) 2005-2013 Rich Felker. All rights reserved.
 * Copyright (c) 2013 The F9 Microkernel Project. All rights reserved.
 * Use of this source code is governed by MIT license that can be found
 * in the LICENSE file.
 */

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

void *memset(void *dest, int c, size_t n)
{
	unsigned char *s = dest;
	size_t k;
#ifdef __GNUC__
	typedef uint32_t __attribute__((__may_alias__)) u32;
	typedef uint64_t __attribute__((__may_alias__)) u64;
	u32 c32;
	u64 c64;
#endif

	/* Fill head and tail with minimal branching. Each
	 * conditional ensures that all the subsequently used
	 * offsets are well-defined and in the dest region.
	 */

	if (!n)
		return dest;
	s[0] = s[n - 1] = c;
	if (n <= 2)
		return dest;
	s[1] = s[n - 2] = c;
	s[2] = s[n - 3] = c;
	if (n <= 6)
		return dest;
	s[3] = s[n - 4] = c;
	if (n <= 8)
		return dest;

	/* Advance pointer to align it at a 4-byte boundary,
	 * and truncate n to a multiple of 4. The previous code
	 * already took care of any head/tail that get cut off
	 * by the alignment.
	 */

	k = - (uintptr_t) s & 3;
	s += k;
	n -= k;
	n &= -4;

#ifdef __GNUC__
	c32 = ((u32) - 1) / 255 * (unsigned char) c;
	/* In preparation to copy 32 bytes at a time, aligned on
	 * an 8-byte bounary, fill head/tail up to 28 bytes each.
	 * As in the initial byte-based head/tail fill, each
	 * conditional below ensures that the subsequent offsets
	 * are valid (e.g. !(n<=24) implies n>=28).
	 */

	*(u32 *)(s + 0) = c32;
	*(u32 *)(s + n - 4) = c32;
	if (n <= 8)
		return dest;
	*(u32 *)(s + 4) = c32;
	*(u32 *)(s + 8) = c32;
	*(u32 *)(s + n - 12) = c32;
	*(u32 *)(s + n - 8) = c32;
	if (n <= 24)
		return dest;
	*(u32 *)(s + 12) = c32;
	*(u32 *)(s + 16) = c32;
	*(u32 *)(s + 20) = c32;
	*(u32 *)(s + 24) = c32;
	*(u32 *)(s + n - 28) = c32;
	*(u32 *)(s + n - 24) = c32;
	*(u32 *)(s + n - 20) = c32;
	*(u32 *)(s + n - 16) = c32;

	/* Align to a multiple of 8 so we can fill 64 bits at a time,
	 * and avoid writing the same bytes twice as much as is
	 * practical without introducing additional branching.
	 */

	k = 24 + ((uintptr_t) s & 4);
	s += k;
	n -= k;

	/* If this loop is reached, 28 tail bytes have already been
	 * filled, so any remainder when n drops below 32 can be
	 * safely ignored.
	 */

	c64 = c32 | ((u64)c32 << 32);
	for (; n >= 32; n -= 32, s += 32) {
		*(u64 *)(s + 0) = c64;
		*(u64 *)(s + 8) = c64;
		*(u64 *)(s + 16) = c64;
		*(u64 *)(s + 24) = c64;
	}
#else
	/* Pure C fallback with no aliasing violations. */
	for (; n; n--, s++)
		*s = c;
#endif

	return dest;
}