swapmem.c   [plain text]

/***********************************************************************
*                                                                      *
*               This software is part of the ast package               *
*          Copyright (c) 1985-2007 AT&T Intellectual Property          *
*                      and is licensed under the                       *
*                  Common Public License, Version 1.0                  *
*                    by AT&T Intellectual Property                     *
*                                                                      *
*                A copy of the License is available at                 *
*            http://www.opensource.org/licenses/cpl1.0.txt             *
*         (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9)         *
*                                                                      *
*              Information and Software Systems Research               *
*                            AT&T Research                             *
*                           Florham Park NJ                            *
*                                                                      *
*                 Glenn Fowler <gsf@research.att.com>                  *
*                  David Korn <dgk@research.att.com>                   *
*                   Phong Vo <kpv@research.att.com>                    *
*                                                                      *
***********************************************************************/
#pragma prototyped
/*
 * Glenn Fowler
 * AT&T Research
 *
 * internal representation conversion support
 */

#include <ast.h>
#include <swap.h>

/*
 * swap n bytes according to op
 * from==to is ok
 */

void*
swapmem(int op, const void* from, void* to, register size_t n)
{
	register char*	f = (char*)from;
	register char*	t = (char*)to;
	register int	c;

	switch (op & (n - 1))
	{
	case 0:
		if (t != f)
			memcpy(t, f, n);
		break;
	case 1:
		for (n >>= 1; n--; f += 2, t += 2)
		{
			c = f[0]; t[0] = f[1]; t[1] = c;
		}
		break;
	case 2:
		for (n >>= 2; n--; f += 4, t += 4)
		{
			c = f[0]; t[0] = f[2]; t[2] = c;
			c = f[1]; t[1] = f[3]; t[3] = c;
		}
		break;
	case 3:
		for (n >>= 2; n--; f += 4, t += 4)
		{
			c = f[0]; t[0] = f[3]; t[3] = c;
			c = f[1]; t[1] = f[2]; t[2] = c;
		}
		break;
	case 4:
		for (n >>= 3; n--; f += 8, t += 8)
		{
			c = f[0]; t[0] = f[4]; t[4] = c;
			c = f[1]; t[1] = f[5]; t[5] = c;
			c = f[2]; t[2] = f[6]; t[6] = c;
			c = f[3]; t[3] = f[7]; t[7] = c;
		}
		break;
	case 5:
		for (n >>= 3; n--; f += 8, t += 8)
		{
			c = f[0]; t[0] = f[5]; t[5] = c;
			c = f[1]; t[1] = f[4]; t[4] = c;
			c = f[2]; t[2] = f[7]; t[7] = c;
			c = f[3]; t[3] = f[6]; t[6] = c;
		}
		break;
	case 6:
		for (n >>= 3; n--; f += 8, t += 8)
		{
			c = f[0]; t[0] = f[6]; t[6] = c;
			c = f[1]; t[1] = f[7]; t[7] = c;
			c = f[2]; t[2] = f[4]; t[4] = c;
			c = f[3]; t[3] = f[5]; t[5] = c;
		}
		break;
	case 7:
		for (n >>= 3; n--; f += 8, t += 8)
		{
			c = f[0]; t[0] = f[7]; t[7] = c;
			c = f[1]; t[1] = f[6]; t[6] = c;
			c = f[2]; t[2] = f[5]; t[5] = c;
			c = f[3]; t[3] = f[4]; t[4] = c;
		}
		break;
	}
	return to;
}