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175 lines
7.6 KiB
C
175 lines
7.6 KiB
C
/*****************************************************************************/
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/* */
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/* posix_memalign */
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/* */
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/* Allocate an aligned memory block */
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/* */
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/* */
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/* */
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/* (C) 2004-2005 Ullrich von Bassewitz */
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/* Roemerstrasse 52 */
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/* D-70794 Filderstadt */
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/* EMail: uz@cc65.org */
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/* */
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/* */
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/* This software is provided "as-is," without any expressed or implied */
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/* warranty. In no event will the authors be held liable for any damages */
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/* arising from the use of this software. */
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/* */
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/* Permission is granted to anyone to use this software for any purpose, */
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/* including commercial applications, and to alter it and redistribute it */
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/* freely, subject to the following restrictions: */
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/* */
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/* 1. The origin of this software must not be misrepresented; you must not */
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/* claim that you wrote the original software. If you use this software */
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/* in a product, an acknowledgment in the product documentation would be */
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/* appreciated, but is not required. */
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/* 2. Alterred source versions must be marked plainly as such, and must not */
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/* be misrepresented as being the original software. */
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/* 3. This notice may not be removed or alterred from any source */
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/* distribution. */
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/* */
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/*****************************************************************************/
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#include <stddef.h> /* define NULL */
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#include <stdlib.h> /* declare function's prototype */
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#include <_heap.h>
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#include <errno.h>
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#define EOK 0 /* No errors (non-standard name) */
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/* This is a very simple version of an aligned memory allocator. We will
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** allocate a greater block, so that we can place the aligned block (that is
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** returned) within it. We use our knowledge about the internal heap
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** structures to free the unused parts of the bigger block (the two chunks
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** below and above the aligned block).
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*/
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int __fastcall__ posix_memalign (void** memptr, size_t alignment, size_t size)
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/* Allocate a block of memory with the given "size", which is aligned to a
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** memory address that is a multiple of "alignment". "alignment" MUST NOT be
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** zero, and MUST be a power of two; otherwise, this function will return
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** EINVAL. The function returns ENOMEM if not enough memory is available
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** to satisfy the request. "memptr" must point to a variable; that variable
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** will return the address of the allocated memory. Use free() to release that
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** allocated block.
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*/
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{
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size_t rawsize;
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size_t uppersize;
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size_t lowersize;
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register struct usedblock* b; /* points to raw Block */
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register struct usedblock* u; /* points to User block */
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register struct usedblock* p; /* Points to upper block */
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/* Handle requests for zero-sized blocks */
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if (size == 0) {
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*memptr = NULL;
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return EINVAL;
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}
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/* Test alignment: is it a power of two? There must be only one bit set. */
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if (alignment == 0 || (alignment & --alignment) != 0) {
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*memptr = NULL;
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return EINVAL;
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}
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/* Augment the block size up to the alignment, and allocate memory.
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** We don't need to account for the additional admin. data that's needed to
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** manage the used block, because the block returned by malloc() has that
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** overhead added one time; and, the worst thing that might happen is that
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** we cannot free the upper and lower blocks.
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*/
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b = malloc (size + alignment);
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/* Handle out-of-memory */
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if (b == NULL) {
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*memptr = NULL;
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return ENOMEM;
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}
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/* Create (and return) a new pointer that points to the user-visible
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** aligned block.
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*/
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u = *memptr = (struct usedblock*) (((unsigned)b + alignment) & ~alignment);
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/* Get a pointer to the (raw) upper block */
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p = (struct usedblock*) ((char*)u + size);
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/* Get the raw-block pointer, which is located just below the visible
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** unaligned block. The first word of this raw block is the total size
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** of the block, including the admin. space.
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*/
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b = (b-1)->start;
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rawsize = b->size;
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/* Check if we can free the space above the user block. That is the case
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** if the size of the block is at least sizeof (struct freeblock) bytes,
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** and the size of the remaining block is at least that size, too.
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** If the upper block is smaller, then we just will pass it to the caller,
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** together with the requested aligned block.
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*/
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uppersize = rawsize - (lowersize = (char*)p - (char*)b);
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if (uppersize >= sizeof (struct freeblock) &&
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lowersize >= sizeof (struct freeblock)) {
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/* Setup the usedblock structure */
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p->size = uppersize;
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p->start = p;
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/* Generate a pointer to the (upper) user space, and free that block */
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free (p + 1);
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/* Decrease the raw-block size by the amount of space just freed */
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rawsize = lowersize;
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}
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/* Check if we can free the space below the user block. That is the case
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** if the size of the block is at least sizeof (struct freeblock) bytes,
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** and the size of the remaining block is at least that size, too. If the
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** lower block is smaller, we just will pass it to the caller, together
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** with the requested aligned block.
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** Beware: We need an additional struct usedblock, in the lower block,
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** which is part of the block that is passed back to the caller.
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*/
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lowersize = ((char*)u - (char*)b) - sizeof (struct usedblock);
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if ( lowersize >= sizeof (struct freeblock) &&
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(rawsize - lowersize) >= sizeof (struct freeblock)) {
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/* b already points to the raw lower-block.
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** Set up the usedblock structure.
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*/
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b->size = lowersize;
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b->start = b;
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/* Generate a pointer to the (lower) user space, and free that block */
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free (b + 1);
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/* Decrease the raw-block size by the amount of space just freed */
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rawsize -= lowersize;
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/* Set b to the raw user-block (that will be returned) */
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b = u - 1;
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}
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/* u points to the user-visible block, while b points to the raw block,
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** and rawsize contains the length of the raw block. Set up the usedblock
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** structure, but beware: If we didn't free the lower block, then it is
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** split; which means that we must use b to write the size,
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** and u to write the start field.
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*/
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b->size = rawsize;
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(u-1)->start = b;
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return EOK;
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}
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