119 lines
3.0 KiB
C
119 lines
3.0 KiB
C
#if !defined(lint) && defined(SCCSIDS)
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static char sccsid[] = "@(#)memalign.c 1.1 94/10/31 Copyr 1984 Sun Micro";
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#endif
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#include "mallint.h"
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#include <errno.h>
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extern int errno;
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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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char *
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memalign(align, nbytes)
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uint align;
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uint nbytes;
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{
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uint reqsize; /* Num of bytes to get from malloc() */
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register char *p; /* Ptr returned from malloc() */
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register Dblk blk; /* For addressing fragment blocks */
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register uint blksize; /* Current (shrinking) block size */
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register char *alignedp; /* Ptr to properly aligned boundary */
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register Dblk aligned_blk; /* The block to be returned */
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register uint frag_size; /* size of fragments fore and aft */
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uint x; /* ccom can't do (char*)(uint/uint) */
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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)) {
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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.
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*/
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nbytes = roundup(nbytes, ALIGNSIZ);
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reqsize = nbytes + align + SMALLEST_BLK;
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p = malloc(reqsize);
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if (p == NULL) {
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return NULL;
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}
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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 = (Dblk)(p - ALIGNSIZ); /* back up to get length word */
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blksize = blk->size;
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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 = roundup((uint)p, align); /* ccom work-around */
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alignedp = (char *)x;
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aligned_blk = (Dblk)(alignedp - ALIGNSIZ);
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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 = (uint)aligned_blk - (uint)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 < SMALLEST_BLK ) {
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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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*/
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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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blk->size = frag_size;
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blksize -= frag_size;
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aligned_blk->size = blksize;
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free(blk->data);
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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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nbytes += ALIGNSIZ;
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frag_size = blksize - nbytes;
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if (frag_size > SMALLEST_BLK) {
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/*
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* split and free a fragment on the right
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*/
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blk = nextblk(aligned_blk, nbytes);
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blk->size = frag_size;
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aligned_blk->size -= frag_size;
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free(blk->data);
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}
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return(aligned_blk->data);
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}
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