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Optimize memcpy(3).

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This commit is contained in:
Jonas 'Sortie' Termansen 2012-12-05 17:34:28 +01:00
parent 3116161f5d
commit 1b0ddadab3
1 changed files with 98 additions and 29 deletions
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127
libc/memcpy.cpp
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@ -25,37 +25,106 @@
#include <stdint.h>
#include <string.h>
static void* memcpy_aligned(unsigned long* dest,
const unsigned long* src,
size_t length)
{
size_t numcopies = length / sizeof(unsigned long);
for ( size_t i = 0; i < numcopies; i++ )
dest[i] = src[i];
return dest;
}
#undef restrict
#define restrict __restrict__
static inline bool IsWordAligned(uintptr_t addr)
{
const size_t WORDSIZE = sizeof(unsigned long);
return (addr / WORDSIZE * WORDSIZE) == addr;
}
#if 8 < __SIZEOF_LONG__
#error unsigned long is bigger than expected, please add support to this file.
#endif
extern "C" void* memcpy(void* destptr, const void* srcptr, size_t length)
inline static void* memcpy_slow(void* restrict dstptr,
const void* restrict srcptr, size_t length)
{
if ( IsWordAligned((uintptr_t) destptr) &&
IsWordAligned((uintptr_t) srcptr) &&
IsWordAligned(length) )
{
unsigned long* dest = (unsigned long*) destptr;
const unsigned long* src = (const unsigned long*) srcptr;
return memcpy_aligned(dest, src, length);
}
uint8_t* dest = (uint8_t*) destptr;
const uint8_t* src = (const uint8_t*) srcptr;
uint8_t* restrict dst = (uint8_t* restrict) dstptr;
const uint8_t* restrict src = (const uint8_t* restrict) srcptr;
for ( size_t i = 0; i < length; i += sizeof(uint8_t) )
{
dest[i] = src[i];
}
return dest;
dst[i] = src[i];
return dstptr;
}
extern "C" void* memcpy(void* restrict dstptr, const void* restrict srcptr,
size_t length)
{
const unsigned long unalignmask = sizeof(unsigned long) - 1;
const unsigned long srcunalign = (unsigned long) srcptr & unalignmask;
const unsigned long dstunalign = (unsigned long) dstptr & unalignmask;
if ( srcunalign != dstunalign )
return memcpy_slow(dstptr, srcptr, length);
union
{
unsigned long srcval;
const uint8_t* restrict src8;
const uint16_t* restrict src16;
const uint32_t* restrict src32;
const uint64_t* restrict src64;
const unsigned long* restrict srcul;
};
srcval = (unsigned long) srcptr;
union
{
unsigned long dstval;
uint8_t* restrict dst8;
uint16_t* restrict dst16;
uint32_t* restrict dst32;
uint64_t* restrict dst64;
unsigned long* restrict dstul;
};
dstval = (unsigned long) dstptr;
if ( dstunalign )
{
if ( 1 <= length && !(dstval & (1-1)) && (dstval & (2-1)) )
*dst8++ = *src8++,
length -= 1;
if ( 2 <= length && !(dstval & (2-1)) && (dstval & (4-1)) )
*dst16++ = *src16++,
length -= 2;
#if 8 <= __SIZEOF_LONG__
if ( 4 <= length && !(dstval & (4-1)) && (dstval & (8-1)) )
*dst32++ = *src32++,
length -= 4;
#endif
}
size_t numcopies = length / sizeof(unsigned long);
#if defined(__x86_64__) || defined(__i386__)
unsigned long zeroed_numcopies;
#if defined(__x86_64__)
asm volatile ("rep movsq" : "=c"(zeroed_numcopies), "=S"(srcul), "=D"(dstul)
: "c"(numcopies), "S"(srcul), "D"(dstul)
: "memory");
#elif defined(__i386__)
asm volatile ("rep movsd" : "=c"(zeroed_numcopies), "=S"(srcul), "=D"(dstul)
: "c"(numcopies), "S"(srcul), "D"(dstul)
: "memory");
#endif
#else
for ( size_t i = 0; i < numcopies; i++ )
*dstul++ = *srcul++;
#endif
length -= numcopies * sizeof(unsigned long);
if ( length )
{
#if 8 <= __SIZEOF_LONG__
if ( 4 <= length )
*dst32++ = *src32++,
length -= 4;
#endif
if ( 2 <= length )
*dst16++ = *src16++,
length -= 2;
if ( 1 <= length )
*dst8++ = *src8++,
length -= 1;
}
return dstptr;
}