/*

 * CDDL HEADER START

 *

 * The contents of this file are subject to the terms of the

 * Common Development and Distribution License, Version 1.0 only

 * (the "License").  You may not use this file except in compliance

 * with the License.

 *

 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE

 * or http://www.opensolaris.org/os/licensing.

 * See the License for the specific language governing permissions

 * and limitations under the License.

 *

 * When distributing Covered Code, include this CDDL HEADER in each

 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.

 * If applicable, add the following below this CDDL HEADER, with the

 * fields enclosed by brackets "[]" replaced with your own identifying

 * information: Portions Copyright [yyyy] [name of copyright owner]

 *

 * CDDL HEADER END

 */

/*

 * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.

 * Use is subject to license terms.

 */

#pragma ident	"%Z%%M%	%I%	%E% SMI"

/*	Copyright (c) 1988 AT&T	*/

/*	  All Rights Reserved  	*/

#pragma weak memalign = _memalign

#include "synonyms.h"

#include "mallint.h"

#include "mtlib.h"

#define	_misaligned(p)		((unsigned)(p) & 3)

		/* 4-byte "word" alignment is considered ok in LP64 */

#define	_nextblk(p, size)	((TREE *)((uintptr_t)(p) + (size)))

/*

 * memalign(align, nbytes)

 *

 * Description:

 *	Returns a block of specified size on a specified alignment boundary.

 *

 * Algorithm:

 *	Malloc enough to ensure that a block can be aligned correctly.

 *	Find the alignment point and return the fragments

 *	before and after the block.

 *

 * Errors:

 *	Returns NULL and sets errno as follows:

 *	[EINVAL]

 *		if nbytes = 0,

 *		or if alignment is misaligned,

 *		or if the heap has been detectably corrupted.

 *	[ENOMEM]

 *		if the requested memory could not be allocated.

 */

void *

memalign(size_t align, size_t nbytes)

{

	size_t	 reqsize;	/* Num of bytes to get from malloc() */

	TREE	*p;		/* Ptr returned from malloc() */

	TREE	*blk;		/* For addressing fragment blocks */

	size_t	blksize;	/* Current (shrinking) block size */

	TREE	*alignedp;	/* Ptr to properly aligned boundary */

	TREE	*aligned_blk;	/* The block to be returned */

	size_t	frag_size;	/* size of fragments fore and aft */

	size_t	 x;

	/*

	 * check for valid size and alignment parameters

	 * MAX_ALIGN check prevents overflow in later calculation.

	 */

	if (nbytes == 0 || _misaligned(align) || align == 0 ||

	    align > MAX_ALIGN) {

		errno = EINVAL;

		return (NULL);

	}

	/*

	 * Malloc enough memory to guarantee that the result can be

	 * aligned correctly. The worst case is when malloc returns

	 * a block so close to the next alignment boundary that a

	 * fragment of minimum size cannot be created.  In order to

	 * make sure we can handle this, we need to force the

	 * alignment to be at least as large as the minimum frag size

	 * (MINSIZE + WORDSIZE).

	 */

	/* check for size that could overflow calculations */

	if (nbytes > MAX_MALLOC) {

		errno = ENOMEM;

		return (NULL);

	}

	ROUND(nbytes);

	if (nbytes < MINSIZE)

		nbytes = MINSIZE;

	ROUND(align);

	while (align < MINSIZE + WORDSIZE)

		align <<= 1;

	reqsize = nbytes + align + (MINSIZE + WORDSIZE);

	/* check for overflow */

	if (reqsize < nbytes) {

		errno = ENOMEM;

		return (NULL);

	}

	p = (TREE *)malloc(reqsize);

	if (p == (TREE *)NULL) {

		/* malloc sets errno */

		return (NULL);

	}

	lmutex_lock(&libc_malloc_lock);

	/*

	 * get size of the entire block (overhead and all)

	 */

	blk = BLOCK(p);			/* back up to get length word */

	blksize = SIZE(blk);

	CLRBITS01(blksize);

	/*

	 * locate the proper alignment boundary within the block.

	 */

	x = (size_t)p;

	if (x % align != 0)

		x += align - (x % align);

	alignedp = (TREE *)x;

	aligned_blk = BLOCK(alignedp);

	/*

	 * Check out the space to the left of the alignment

	 * boundary, and split off a fragment if necessary.

	 */

	frag_size = (size_t)aligned_blk - (size_t)blk;

	if (frag_size != 0) {

		/*

		 * Create a fragment to the left of the aligned block.

		 */

		if (frag_size < MINSIZE + WORDSIZE) {

			/*

			 * Not enough space. So make the split

			 * at the other end of the alignment unit.

			 * We know this yields enough space, because

			 * we forced align >= MINSIZE + WORDSIZE above.

			 */

			frag_size += align;

			aligned_blk = _nextblk(aligned_blk, align);

		}

		blksize -= frag_size;

		SIZE(aligned_blk) = blksize | BIT0;

		frag_size -= WORDSIZE;

		SIZE(blk) = frag_size | BIT0 | ISBIT1(SIZE(blk));

		_free_unlocked(DATA(blk));

	}

	/*

	 * Is there a (sufficiently large) fragment to the

	 * right of the aligned block?

	 */

	frag_size = blksize - nbytes;

	if (frag_size >= MINSIZE + WORDSIZE) {

		/*

		 * split and free a fragment on the right

		 */

		blksize = SIZE(aligned_blk);

		SIZE(aligned_blk) = nbytes;

		blk = NEXT(aligned_blk);

		SETOLD01(SIZE(aligned_blk), blksize);

		frag_size -= WORDSIZE;

		SIZE(blk) = frag_size | BIT0;

		_free_unlocked(DATA(blk));

	}

	lmutex_unlock(&libc_malloc_lock);

	return (DATA(aligned_blk));

}