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164 lines
6.9 KiB
C
164 lines
6.9 KiB
C
/*****************************************************************************/
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/* */
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/* _aligned_malloc */
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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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/* Römerstrasse 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. Altered source versions must be plainly marked 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 altered from any source */
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/* distribution. */
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/* */
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/*****************************************************************************/
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#include <stdlib.h>
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#include <_heap.h>
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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 we can place the aligned block within it
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* that is returned. 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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void* __fastcall__ _aligned_malloc (size_t size, size_t alignment)
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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 a call to this function will
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* cause undefined behaviour. The function returns NULL if not enough memory
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* is available to satisfy the request. To free the allocated block, use the
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* free() function.
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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;
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register struct usedblock* u;
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register struct usedblock* p;
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/* Handle requests for zero sized blocks */
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if (size == 0) {
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return 0;
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}
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/* We don't really need alignment, but alignment-1 */
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--alignment;
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/* Round up the block size and allocate memory. We don't need to account
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* for the additional admin data needed to manage the used block, since
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* the block returned by malloc has this overhead added one time, and
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* the worst thing that may happen is that we cannot free the upper and
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* 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 == 0) {
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return 0;
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}
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/* Create a new pointer that points to the user visible aligned block. */
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u = (struct usedblock*) (((unsigned)b + alignment) & ~alignment);
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/* Get the raw block pointer, which is located just below the user visible
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* block. The first word of this raw block is the total size of the block
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* 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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/* Get a pointer to the (raw) upper block */
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p = (struct usedblock*) (size + (unsigned)u);
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/* Check if we can free the space above the allocated block. This is the
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* case if the size of the block is at least sizeof (struct freeblock)
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* bytes and the size of the remaining block is at least of this size,
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* too. If the upper block is smaller, we will just 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 + (unsigned)b - (unsigned)p;
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if (uppersize >= sizeof (struct freeblock) &&
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(rawsize - uppersize) >= 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 user space and free the block */
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free (p + 1);
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/* Decrement the raw block size by the amount of space just free'd */
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rawsize -= uppersize;
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}
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/* Check if we can free the space below the allocated block. This is the
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* case, if the size of the block is at least sizeof (struct freeblock)
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* bytes and the size of the remaining block is at least of this size,
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* too. If the lower block is smaller, we will just pass it to the caller
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* together with the requested aligned block.
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* Beware: We need an additional struct usedblock in the lower block which
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* is part of the block that is passed back to the caller.
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*/
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lowersize = ((unsigned)u - (unsigned)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 does already point to the raw lower block. Setup the usedblock
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* 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 user space and free the block */
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free (b + 1);
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/* Decrement the raw block size by the amount of space just free'd */
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rawsize -= lowersize;
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/* Set b to the raw user block */
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b = u - 1;
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}
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/* u does now point to the user visible block, while b points to the raw
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* block, and rawsize contains the size of the raw block. Setup the
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* usedblock structure but beware: If we didn't free the lower block, it
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* is splitted, which means that we must use u to write the start field,
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* and b to write the size.
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*/
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(u-1)->start = b;
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b->size = rawsize;
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/* Return the user portion of the aligned block */
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return u;
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}
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