memcpy
#include <stddef.h> //
#include <stdint.h> //uintptr_t is quoted.
#include "string.h"
/*
* sizeof(word) MUST BE A POWER OF TWO
* SO THAT wmask BELOW IS ALL ONES
*/
typedef int word; /* "word" used for optimal copy speed */ #define wsize sizeof(word)
#define wmask (wsize - 1) /*
* Copy a block of memory, handling overlap.
* This is the routine that actually implements
* (the portable versions of) bcopy, memcpy, and memmove.
*/ __private_extern__
void * memcpy(void *dst0, const void *src0, size_t length)
{
char *dst = dst0;
const char *src = src0;
size_t t; if (length == || dst == src) /* nothing to do */
goto done; /*
* Macros: loop-t-times; and loop-t-times, t>0
*/
#define TLOOP(s) if (t) TLOOP1(s)
#define TLOOP1(s) do { s; } while (--t) if ((unsigned long)dst < (unsigned long)src) {
/*
* Copy forward.
*/
t = (uintptr_t)src; /* only need low bits */
if ((t | (uintptr_t)dst) & wmask) {
/*
* Try to align operands. This cannot be done
* unless the low bits match.
*/
if ((t ^ (uintptr_t)dst) & wmask || length < wsize)
t = length;
else
t = wsize - (t & wmask);
length -= t;
TLOOP1(*dst++ = *src++);
}
/*
* Copy whole words, then mop up any trailing bytes.
*/
t = length / wsize;
TLOOP(*(word *)dst = *(word *)src; src += wsize; dst += wsize);
t = length & wmask;
TLOOP(*dst++ = *src++);
} else {
/*
* Copy backwards. Otherwise essentially the same.
* Alignment works as before, except that it takes
* (t&wmask) bytes to align, not wsize-(t&wmask).
*/
src += length;
dst += length;
t = (uintptr_t)src;
if ((t | (uintptr_t)dst) & wmask) {
if ((t ^ (uintptr_t)dst) & wmask || length <= wsize)
t = length;
else
t &= wmask;
length -= t;
TLOOP1(*--dst = *--src);
}
t = length / wsize;
TLOOP(src -= wsize; dst -= wsize; *(word *)dst = *(word *)src);
t = length & wmask;
TLOOP(*--dst = *--src);
}
done:
return (dst0);
} __private_extern__ void *
memmove(void *s1, const void *s2, size_t n)
{
return memcpy(s1, s2, n);
} __private_extern__ void
bcopy(const void *s1, void *s2, size_t n)
{
memcpy(s2, s1, n);
http://www.opensource.apple.com/source/xnu/xnu-2050.18.24/libsyscall/wrappers/memcpy.c
intptr_t
http://www.cnblogs.com/aprilapril/p/4318769.html