memcpy.c File Reference

#include <string.h>

Include dependency graph for memcpy.c:

Go to the source code of this file.

Macros
#define	wsize   sizeof(word)
#define	wmask   (wsize - 1)
#define	TLOOP(s)   if (t) TLOOP1(s)
#define	TLOOP1(s)   do { s; } while (--t)

Typedefs
typedef int	word

Functions
void *	memcpy (void *dst0, const void *src0, size_t length)

Macro Definition Documentation

TLOOP

#define TLOOP

(

s

)

if (t) TLOOP1(s)

TLOOP1

#define TLOOP1

(

s

)

do { s; } while (--t)

wmask

#define wmask   (wsize - 1)

Definition at line 42 of file memcpy.c.

wsize

#define wsize   sizeof(word)

Definition at line 41 of file memcpy.c.

Typedef Documentation

word

typedef int word

Definition at line 39 of file memcpy.c.

Function Documentation

memcpy()

void* memcpy	(	void *	dst0,
		const void *	src0,
		size_t	length
	)

Definition at line 49 of file memcpy.c.

{
    char* dst = dst0;
    const char* src = src0;
    size_t t;

    if(length == 0 || dst == src)
    {
        { /* nothing to do */
            goto done;
        }
    }

/*
 * Macros: loop-t-times; and loop-t-times, t>0
 */
// clang-format off
#define TLOOP(s) if (t) TLOOP1(s)
#define TLOOP1(s) do { s; } while (--t)
    // clang-format on

    if((uintptr_t)dst < (uintptr_t)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;
        // Silence warning for alignment change by casting to void*
        TLOOP(*(word*)(void*)dst = *(const word*)(const void*)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;
        // Silence warning for alignment change by casting to void*
        TLOOP(src -= wsize; dst -= wsize; *(word*)(void*)dst = *(const word*)(const void*)src);
        t = length & wmask;
        TLOOP(*--dst = *--src);
    }
done:
    return (dst0);
}

References TLOOP, TLOOP1, wmask, and wsize.