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337 lines
8.3 KiB
ArmAsm
337 lines
8.3 KiB
ArmAsm
;
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; Ullrich von Bassewitz, 17.7.2000
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;
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; Allocate a block from the heap.
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;
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; void* __fastcall__ malloc (size_t size);
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;
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;
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; C implementation was:
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;
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; void* malloc (size_t size)
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; /* Allocate memory from the given heap. The function returns a pointer to the
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; * allocated memory block or a NULL pointer if not enough memory is available.
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; * Allocating a zero size block is not allowed.
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; */
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; {
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; struct freeblock* f;
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; unsigned* p;
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;
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;
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; /* Check for a size of zero, then add the administration space and round
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; * up the size if needed.
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; */
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; if (size == 0) {
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; return 0;
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; }
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; size += HEAP_ADMIN_SPACE;
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; if (size < sizeof (struct freeblock)) {
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; size = sizeof (struct freeblock);
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; }
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;
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; /* Search the freelist for a block that is big enough */
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; f = _hfirst;
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; while (f && f->size < size) {
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; f = f->next;
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; }
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;
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; /* Did we find one? */
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; if (f) {
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;
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; /* We found a block big enough. If the block can hold just the
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; * requested size, use the block in full. Beware: When slicing blocks,
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; * there must be space enough to create a new one! If this is not the
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; * case, then use the complete block.
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; */
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; if (f->size - size < sizeof (struct freeblock)) {
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;
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; /* Use the actual size */
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; size = f->size;
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;
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; /* Remove the block from the free list */
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; if (f->prev) {
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; /* We have a previous block */
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; f->prev->next = f->next;
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; } else {
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; /* This is the first block, correct the freelist pointer */
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; _hfirst = f->next;
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; }
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; if (f->next) {
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; /* We have a next block */
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; f->next->prev = f->prev;
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; } else {
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; /* This is the last block, correct the freelist pointer */
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; _hlast = f->prev;
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; }
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;
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; } else {
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;
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; /* We must slice the block found. Cut off space from the upper
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; * end, so we can leave the actual free block chain intact.
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; */
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;
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; /* Decrement the size of the block */
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; f->size -= size;
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;
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; /* Set f to the now unused space above the current block */
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; f = (struct freeblock*) (((unsigned) f) + f->size);
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;
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; }
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;
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; /* Setup the pointer for the block */
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; p = (unsigned*) f;
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;
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; } else {
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;
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; /* We did not find a block big enough. Try to use new space from the
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; * heap top.
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; */
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; if (((unsigned) _hend) - ((unsigned) _hptr) < size) {
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; /* Out of heap space */
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; return 0;
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; }
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;
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;
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; /* There is enough space left, take it from the heap top */
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; p = _hptr;
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; _hptr = (unsigned*) (((unsigned) _hptr) + size);
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;
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; }
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;
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; /* New block is now in p. Fill in the size and return the user pointer */
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; *p++ = size;
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; return p;
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; }
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;
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.importzp ptr1, ptr2, ptr3
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.import __hptr, __hfirst, __hlast, __hend
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.export _malloc
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.macpack generic
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; Offsets into struct freeblock and other constant stuff
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size = 0
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next = 2
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prev = 4
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admin_space = 2
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min_size = 6
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; Code
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_malloc:
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sta ptr1 ; Store size in ptr1
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stx ptr1+1
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; Check for a size of zero, if so, return NULL
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ora ptr1+1
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beq Done ; a/x already contains zero
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; Add the administration space and round up the size if needed
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lda ptr1
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add #admin_space
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sta ptr1
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bcc @L1
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inc ptr1+1
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@L1: ldx ptr1+1
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bne @L2
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cmp #min_size+1
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bcs @L2
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lda #min_size
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sta ptr1 ; High byte is already zero
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; Load a pointer to the freelist into ptr2
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@L2: lda __hfirst
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sta ptr2
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lda __hfirst+1
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sta ptr2+1
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; Search the freelist for a block that is big enough. We will calculate
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; (f->size - size) here and keep it, since we need the value later.
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jmp @L4
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@L3: ldy #size
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lda (ptr2),y
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sub ptr1
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tax ; Remember low byte for later
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iny ; Y points to size+1
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lda (ptr2),y
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sbc ptr1+1
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bcs BlockFound ; Beware: Contents of a/x/y are known!
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; Next block in list
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iny ; Points to next
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lda (ptr2),y
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tax
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iny ; Points to next+1
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lda (ptr2),y
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stx ptr2
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sta ptr2+1
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@L4: ora ptr2
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bne @L3
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; We did not find a block big enough. Try to use new space from the heap top.
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lda __hptr
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add ptr1 ; _hptr + size
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tay
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lda __hptr+1
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adc ptr1+1
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bcs OutOfHeapSpace ; On overflow, we're surely out of space
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cmp __hend+1
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bne @L5
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cpy __hend
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@L5: bcc TakeFromTop
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beq TakeFromTop
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; Out of heap space
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OutOfHeapSpace:
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lda #0
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tax
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Done: rts
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; There is enough space left, take it from the heap top
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TakeFromTop:
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ldx __hptr ; p = hptr;
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stx ptr2
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ldx __hptr+1
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stx ptr2+1
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sty __hptr ; hptr += size;
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sta __hptr+1
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jmp FillSizeAndRet ; Done
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; We found a block big enough. If the block can hold just the
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; requested size, use the block in full. Beware: When slicing blocks,
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; there must be space enough to create a new one! If this is not the
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; case, then use the complete block.
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; On input, x/a do contain the remaining size of the block. The zero
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; flag is set if the high byte of this remaining size is zero.
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BlockFound:
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bne SliceBlock ; Block is large enough to slice
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cpx #min_size+1 ; Check low byte
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bcs SliceBlock ; Jump if block is large enough to slice
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; The block is too small to slice it. Use the block in full. The block
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; does already contain the correct size word, all we have to do is to
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; remove it from the free list.
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ldy #prev+1 ; Load f->prev
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lda (ptr2),y
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sta ptr3+1
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dey
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lda (ptr2),y
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sta ptr3
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dey ; Points to next+1
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ora ptr3+1
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beq @L1 ; Jump if f->prev zero
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; We have a previous block, ptr3 contains its address.
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; Do f->prev->next = f->next
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lda (ptr2),y ; Load high byte of f->next
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sta (ptr3),y ; Store high byte of f->prev->next
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dey ; Points to next
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lda (ptr2),y ; Load low byte of f->next
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sta (ptr3),y ; Store low byte of f->prev->next
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jmp @L2
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; This is the first block, correct the freelist pointer
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; Do _hfirst = f->next
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@L1: lda (ptr2),y ; Load high byte of f->next
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sta __hfirst+1
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dey ; Points to next
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lda (ptr2),y ; Load low byte of f->next
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sta __hfirst
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; Check f->next. Y points always to next if we come here
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@L2: lda (ptr2),y ; Load low byte of f->next
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sta ptr3
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iny ; Points to next+1
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lda (ptr2),y ; Load high byte of f->next
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sta ptr3+1
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iny ; Points to prev
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ora ptr3
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beq @L3 ; Jump if f->next zero
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; We have a next block, ptr3 contains its address.
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; Do f->next->prev = f->prev
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lda (ptr2),y ; Load low byte of f->prev
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sta (ptr3),y ; Store low byte of f->next->prev
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iny ; Points to prev+1
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lda (ptr2),y ; Load high byte of f->prev
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sta (ptr3),y ; Store high byte of f->prev->next
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jmp RetUserPtr ; Done
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; This is the last block, correct the freelist pointer.
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; Do _hlast = f->prev
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@L3: lda (ptr2),y ; Load low byte of f->prev
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sta __hlast
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iny ; Points to prev+1
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lda (ptr2),y ; Load high byte of f->prev
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sta __hlast+1
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jmp RetUserPtr ; Done
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; We must slice the block found. Cut off space from the upper end, so we
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; can leave the actual free block chain intact.
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SliceBlock:
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; Decrement the size of the block. Y points to size+1.
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dey ; Points to size
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lda (ptr2),y ; Low byte of f->size
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sub ptr1
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sta (ptr2),y
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tax ; Save low byte of f->size in X
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iny ; Points to size+1
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lda (ptr2),y ; High byte of f->size
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sbc ptr1+1
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sta (ptr2),y
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; Set f to the space above the current block, which is the new block returned
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; to the caller.
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txa ; Get low byte of f->size
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add ptr2
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tax
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lda (ptr2),y ; Get high byte of f->size
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adc ptr2+1
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stx ptr2
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sta ptr2+1
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; Fill the size into the admin space of the block and return the user pointer
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FillSizeAndRet:
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ldy #size ; *p = size;
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lda ptr1 ; Low byte of block size
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sta (ptr2),y
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iny ; Points to size+1
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lda ptr1+1
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sta (ptr2),y
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RetUserPtr:
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lda ptr2 ; return ++p;
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ldx ptr2+1
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add #admin_space
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bcc @L9
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inx
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@L9: rts
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