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Add a versin of memset() optimized for speed

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git-svn-id: http://svn.code.sf.net/p/nuttx/code/trunk@5242 42af7a65-404d-4744-a932-0658087f49c3
This commit is contained in:
patacongo
2012-10-21 00:41:44 +00:00
parent 4de5307aa3
commit f16ae329fd
6 changed files with 134 additions and 23 deletions
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nuttx/lib/string/lib_memset.c
+84
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@@ -42,8 +42,12 @@
************************************************************/
#include <nuttx/config.h>
#include <sys/types.h>
#include <stdint.h>
#include <string.h>
#include <assert.h>
/************************************************************
* Global Functions
@@ -52,8 +56,88 @@
#ifndef CONFIG_ARCH_MEMSET
void *memset(void *s, int c, size_t n)
{
#ifdef CONFIG_MEMSET_OPTSPEED
/* This version is optimized for speed (you could do better
* still by exploiting processor caching or memory burst
* knowledge. 64-bit support might improve performance as
* well.
*/
uintptr_t addr = (uintptr_t)s;
uint16_t val16 = ((uint16_t)c << 8) | (uint16_t)c;
uint32_t val32 = ((uint32_t)val16 << 16) | (uint32_t)val16;
/* Make sure that there is something to be cleared */
if (n > 0)
{
/* Align to a 16-bit boundary */
if ((addr & 1) != 0)
{
*(uint8_t*)addr = (uint8_t)c;
addr += 1;
n -= 1;
}
/* Check if there are at least 16-bits left to be zeroed */
if (n >= 2)
{
/* Align to a 32-bit boundary (we know that the destination
* address is already aligned to at least a 16-bit boundary).
*/
if ((addr & 3) != 0)
{
*(uint16_t*)addr = val16;
addr += 2;
n -= 2;
}
/* Loop while there are at least 32-bits left to be zeroed */
while (n >= 4)
{
*(uint32_t*)addr = val32;
addr += 4;
n -= 4;
}
}
/* We may get here under the following conditions:
*
* n = 0, addr may or may not be aligned
* n = 1, addr may or may not be aligned
* n = 2, addr is aligned to a 32-bit boundary
* n = 3, addr is aligned to a 32-bit boundary
*/
switch (n)
{
default:
case 0:
DEBUGASSERT(n == 0);
break;
case 2:
*(uint16_t*)addr = val16;
break;
case 3:
*(uint16_t*)addr = val16;
addr += 2;
case 1:
*(uint8_t*)addr = (uint8_t)c;
break;
}
}
#else
/* This version is optimized for size */
unsigned char *p = (unsigned char*)s;
while (n-- > 0) *p++ = c;
#endif
return s;
}
#endif