150 lines
3.9 KiB
C
Executable File
150 lines
3.9 KiB
C
Executable File
/* Copyright (c) 1988 AT&T */
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/* All Rights Reserved */
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/* THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF AT&T */
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/* The copyright notice above does not evidence any */
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/* actual or intended publication of such source code. */
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#ident "@(#)memalign.c 1.9 93/09/14 SMI" /* SVr4.0 1.3 */
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#ifdef __STDC__
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#pragma weak memalign = _memalign
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#endif
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#include "synonyms.h"
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#include "mallint.h"
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#include <stdlib.h>
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#include <errno.h>
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#define _misaligned(p) ((unsigned)(p)&3)
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#define _nextblk(p, size) ((TREE *) ((char *) (p) + (size)))
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/*
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* memalign(align,nbytes)
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*
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* Description:
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* Returns a block of specified size on a specified alignment boundary.
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*
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* Algorithm:
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* Malloc enough to ensure that a block can be aligned correctly.
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* Find the alignment point and return the fragments
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* before and after the block.
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*
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* Errors:
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* Returns NULL and sets errno as follows:
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* [EINVAL]
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* if nbytes = 0,
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* or if alignment is misaligned,
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* or if the heap has been detectably corrupted.
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* [ENOMEM]
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* if the requested memory could not be allocated.
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*/
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VOID *
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memalign(align, nbytes)
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size_t align;
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size_t nbytes;
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{
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size_t reqsize; /* Num of bytes to get from malloc() */
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register TREE *p; /* Ptr returned from malloc() */
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register TREE *blk; /* For addressing fragment blocks */
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register size_t blksize; /* Current (shrinking) block size */
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register TREE *alignedp; /* Ptr to properly aligned boundary */
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register TREE *aligned_blk; /* The block to be returned */
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register size_t frag_size; /* size of fragments fore and aft */
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size_t x;
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/*
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* check for valid size and alignment parameters
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*/
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if (nbytes == 0 || _misaligned(align) || align == 0) {
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errno = EINVAL;
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return NULL;
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}
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/*
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* Malloc enough memory to guarantee that the result can be
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* aligned correctly. The worst case is when malloc returns
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* a block so close to the next alignment boundary that a
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* fragment of minimum size cannot be created. In order to
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* make sure we can handle this, we need to force the
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* alignment to be at least as large as the minimum frag size
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* (MINSIZE + WORDSIZE).
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*/
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ROUND(nbytes);
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if (nbytes < MINSIZE)
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nbytes = MINSIZE;
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ROUND(align);
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while (align < MINSIZE + WORDSIZE)
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align <<= 1;
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reqsize = nbytes + align + MINSIZE + WORDSIZE;
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p = (TREE *) malloc(reqsize);
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if (p == (TREE *) NULL) {
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errno = ENOMEM;
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return NULL;
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}
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_mutex_lock(&__malloc_lock);
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/*
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* get size of the entire block (overhead and all)
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*/
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blk = BLOCK(p); /* back up to get length word */
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blksize = SIZE(blk);
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CLRBITS01(blksize);
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/*
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* locate the proper alignment boundary within the block.
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*/
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x = (size_t) p;
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if (x % align != 0)
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x += align - (x % align);
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alignedp = (TREE *)x;
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aligned_blk = BLOCK(alignedp);
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/*
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* Check out the space to the left of the alignment
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* boundary, and split off a fragment if necessary.
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*/
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frag_size = (size_t)aligned_blk - (size_t)blk;
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if (frag_size != 0) {
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/*
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* Create a fragment to the left of the aligned block.
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*/
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if (frag_size < MINSIZE + WORDSIZE) {
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/*
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* Not enough space. So make the split
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* at the other end of the alignment unit.
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* We know this yields enough space, because
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* we forced align >= MINSIZE + WORDSIZE above.
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*/
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frag_size += align;
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aligned_blk = _nextblk(aligned_blk,align);
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}
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blksize -= frag_size;
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SIZE(aligned_blk) = blksize | BIT0;
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frag_size -= WORDSIZE;
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SIZE(blk) = frag_size | BIT0 | ISBIT1(SIZE(blk));
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_free_unlocked(DATA(blk));
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}
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/*
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* Is there a (sufficiently large) fragment to the
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* right of the aligned block?
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*/
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frag_size = blksize - nbytes;
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if (frag_size >= MINSIZE + WORDSIZE) {
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/*
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* split and free a fragment on the right
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*/
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blksize = SIZE(aligned_blk);
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SIZE(aligned_blk) = nbytes;
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blk = NEXT(aligned_blk);
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SETOLD01(SIZE(aligned_blk), blksize);
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frag_size -= WORDSIZE;
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SIZE(blk) = frag_size | BIT0;
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_free_unlocked(DATA(blk));
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}
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_mutex_unlock(&__malloc_lock);
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return(DATA(aligned_blk));
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}
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