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#include <string.h>
#include <stdint.h>
void *memset(void *dest, int c, size_t n)
{
unsigned char *s = dest;
size_t k;
/* 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] = c;
s[n-1] = c;
if (n <= 2) return dest;
s[1] = c;
s[2] = c;
s[n-2] = c;
s[n-3] = c;
if (n <= 6) return dest;
s[3] = c;
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__
typedef uint32_t __attribute__((__may_alias__)) u32;
typedef uint64_t __attribute__((__may_alias__)) u64;
u32 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. */
u64 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;
}
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