memcpy.c

来自「Many C samples. It is a good sample for 」· C语言 代码 · 共 44 行

/*  File   : memcpy.c
    Author : Richard A. O'Keefe.
    Updated: 25 May 1984
    Defines: memcpy()

    memcpy(dst, src, len)
    moves len bytes from src to dst.  The result is dst.  This is not
    the same as strncpy or strnmov, while move a maximum of len bytes
    and stop early if they hit a NUL character.  This moves len bytes
    exactly, no more, no less.  See also bcopy() and bmove() which do
    not return a value but otherwise do the same job.

    Note: the VAX assembly code version can only handle 0 <= len < 2^16.
    It is presented for your interest and amusement.
*/

#include "strings.h"

#if	VaxAsm

char *memcpy(dst, src, len)
    char *dst, *src;
    int len;
    {
	asm("movc3 12(ap),*8(ap),*4(ap)");
	return dst;
    }

#else  ~VaxAsm

char *memcpy(dst, src, len)
    char *dst;
    register char *src;
    register int len;
    {
	register char *d;

	for (d = dst; --len >= 0; *d++ = *src++) ;
	return dst;
    }

#endif	VaxAsm