; }
;
- .importzp ptr1, ptr2
- .import __hptr, __hfirst, __hlast
- .import pushax, __hadd
- .export _free
+ .importzp ptr1, ptr2, ptr3, ptr4
+ .import __hptr, __hfirst, __hlast, __hend
+ .export _free, hadd
.macpack generic
; Code
-_free: sta ptr1
- stx ptr1+1 ; Save block
+_free: sta ptr2
+ stx ptr2+1 ; Save block
; Is the argument NULL?
- ora ptr1+1 ; Is the argument NULL?
+ ora ptr2+1 ; Is the argument NULL?
beq @L9 ; Jump if yes
; Decrement the given pointer by the admin space amount, so it points to the
; real block allocated. The size of the block is stored in the admin space.
-; Remember the block size in ptr2.
+; Remember the block size in ptr1.
- lda ptr1
+ lda ptr2
sub #admin_space
- sta ptr1
+ sta ptr2
bcs @L1
- dec ptr1+1
+ dec ptr2+1
@L1: ldy #size+1
- lda (ptr1),y ; High byte of size
- sta ptr2+1 ; Save it
+ lda (ptr2),y ; High byte of size
+ sta ptr1+1 ; Save it
dey
- lda (ptr1),y
- sta ptr2
+ lda (ptr2),y
+ sta ptr1
; Check if the block is on top of the heap
- add ptr1
+ add ptr2
tay
- lda ptr1+1
- adc ptr2+1
+ lda ptr2+1
+ adc ptr1+1
cpy __hptr
- bne @AddToFreeList
+ bne hadd ; Add to free list
cmp __hptr+1
- bne @AddToFreeList
+ bne hadd
; The pointer is located at the heap top. Lower the heap top pointer to
; release the block.
-@L3: lda ptr1
+@L3: lda ptr2
sta __hptr
- lda ptr1+1
+ lda ptr2+1
sta __hptr+1
; Check if the last block in the freelist is now at heap top. If so, remove
; this block from the freelist.
lda __hlast
- sta ptr2
+ sta ptr1
ora __hlast+1
beq @L9 ; Jump if free list empty
lda __hlast+1
- sta ptr2+1 ; Pointer to last block now in ptr2
+ sta ptr1+1 ; Pointer to last block now in ptr1
ldy #size
- lda (ptr2),y ; Low byte of block size
- add ptr2
+ lda (ptr1),y ; Low byte of block size
+ add ptr1
tax
- iny ; High byte of block size
- lda (ptr2),y
- adc ptr2+1
+ iny ; High byte of block size
+ lda (ptr1),y
+ adc ptr1+1
cmp __hptr+1
bne @L9 ; Jump if last block not on top of heap
; Remove the last block
- lda ptr2
+ lda ptr1
sta __hptr
- lda ptr2+1
+ lda ptr1+1
sta __hptr+1
; Correct the next pointer of the now last block
ldy #prev+1 ; Offset of ->prev field
- lda (ptr2),y
- sta ptr1+1 ; Remember f->prev in ptr1
+ lda (ptr1),y
+ sta ptr2+1 ; Remember f->prev in ptr2
sta __hlast+1
dey
- lda (ptr2),y
- sta ptr1 ; Remember f->prev in ptr1
+ lda (ptr1),y
+ sta ptr2 ; Remember f->prev in ptr2
sta __hlast
ora __hlast+1 ; -> prev == 0?
bne @L8 ; Jump if free list not empty
@L9: rts
-; Block before is now last block. ptr1 points to f->prev.
+; Block before is now last block. ptr2 points to f->prev.
@L8: lda #$00
- dey ; Points to high byte of ->next
- sta (ptr1),y
- dey ; Low byte of f->prev->next
- sta (ptr1),y
- rts ; Done
+ dey ; Points to high byte of ->next
+ sta (ptr2),y
+ dey ; Low byte of f->prev->next
+ sta (ptr2),y
+ rts ; Done
+
+; The block is not on top of the heap. Add it to the free list. This was
+; formerly a separate function called __hadd that was implemented in C as
+; shown here:
+;
+; void _hadd (void* mem, size_t size)
+; /* Add an arbitrary memory block to the heap. This function is used by
+; * free(), but it does also allow usage of otherwise unused memory
+; * blocks as heap space. The given block is entered in the free list
+; * without any checks, so beware!
+; */
+; {
+; struct freeblock* f;
+; struct freeblock* left;
+; struct freeblock* right;
+;
+; if (size >= sizeof (struct freeblock)) {
+;
+; /* Set the admin data */
+; f = (struct freeblock*) mem;
+; f->size = size;
+;
+; /* Check if the freelist is empty */
+; if (_hfirst == 0) {
+;
+; /* The freelist is empty until now, insert the block */
+; f->prev = 0;
+; f->next = 0;
+; _hfirst = f;
+; _hlast = f;
+;
+; } else {
+;
+; /* We have to search the free list. As we are doing so, we check
+; * if it is possible to combine this block with another already
+; * existing block. Beware: The block may be the "missing link"
+; * between *two* other blocks.
+; */
+; left = 0;
+; right = _hfirst;
+; while (right && f > right) {
+; left = right;
+; right = right->next;
+; }
+;
+;
+; /* Ok, the current block must be inserted between left and right (but
+; * beware: one of the two may be zero!). Also check for the condition
+; * that we have to merge two or three blocks.
+; */
+; if (right) {
+; /* Check if we must merge the block with the right one */
+; if (((unsigned) f) + size == (unsigned) right) {
+; /* Merge with the right block */
+; f->size += right->size;
+; if (f->next = right->next) {
+; f->next->prev = f;
+; } else {
+; /* This is now the last block */
+; _hlast = f;
+; }
+; } else {
+; /* No merge, just set the link */
+; f->next = right;
+; right->prev = f;
+; }
+; } else {
+; f->next = 0;
+; /* Special case: This is the new freelist end */
+; _hlast = f;
+; }
+; if (left) {
+; /* Check if we must merge the block with the left one */
+; if ((unsigned) f == ((unsigned) left) + left->size) {
+; /* Merge with the left block */
+; left->size += f->size;
+; if (left->next = f->next) {
+; left->next->prev = left;
+; } else {
+; /* This is now the last block */
+; _hlast = left;
+; }
+; } else {
+; /* No merge, just set the link */
+; left->next = f;
+; f->prev = left;
+; }
+; } else {
+; f->prev = 0;
+; /* Special case: This is the new freelist start */
+; _hfirst = f;
+; }
+; }
+; }
+; }
+;
+
+; Check if the free list is empty, storing _hfirst into ptr3 for later
+
+hadd: lda __hfirst
+ sta ptr3
+ lda __hfirst+1
+ sta ptr3+1
+ ora ptr3
+ bne SearchFreeList
+
+; The free list is empty, so this is the first and only block. A contains
+; zero if we come here.
+
+ ldy #next-1
+@L2: iny ; f->next = f->prev = 0;
+ sta (ptr2),y
+ cpy #prev+1 ; Done?
+ bne @L2
+
+ lda ptr2
+ ldx ptr2+1
+ sta __hfirst
+ stx __hfirst+1 ; _hfirst = f;
+ sta __hlast
+ stx __hlast+1 ; _hlast = f;
+
+ rts ; Done
+
+; We have to search the free list. As we are doing so, check if it is possible
+; to combine this block with another, already existing block. Beware: The
+; block may be the "missing link" between two blocks.
+; ptr3 contains _hfirst (the start value of the search) when execution reaches
+; this point, Y contains size+1. We do also know that _hfirst (and therefore
+; ptr3) is not zero on entry.
+
+SearchFreeList:
+ lda #0
+ sta ptr4
+ sta ptr4+1 ; left = 0;
+ ldy #next+1
+ ldx ptr3
+
+@Loop: lda ptr3+1 ; High byte of right
+ cmp ptr2+1
+ bne @L1
+ cpx ptr2
+ beq @L2
+@L1: bcs CheckRightMerge
+
+@L2: stx ptr4 ; left = right;
+ sta ptr4+1
+
+ dey ; Points to next
+ lda (ptr3),y ; right = right->next;
+ tax
+ iny ; Points to next+1
+ lda (ptr3),y
+ stx ptr3
+ sta ptr3+1
+ ora ptr3
+ bne @Loop
+
+; If we come here, the right pointer is zero, so we don't need to check for
+; a merge. The new block is the new freelist end.
+; A is zero when we come here, Y points to next+1
+
+ sta (ptr2),y ; Clear high byte of f->next
+ dey
+ sta (ptr2),y ; Clear low byte of f->next
+
+ lda ptr2 ; _hlast = f;
+ sta __hlast
+ lda ptr2+1
+ sta __hlast+1
+
+; Since we have checked the case that the freelist is empty before, if the
+; right pointer is NULL, the left *cannot* be NULL here. So skip the
+; pointer check and jump right to the left block merge
+
+ jmp CheckLeftMerge2
+
+; The given block must be inserted between left and right, and right is not
+; zero.
+
+CheckRightMerge:
+ lda ptr2
+ add ptr1 ; f + size
+ tax
+ lda ptr2+1
+ adc ptr1+1
+
+ cpx ptr3
+ bne NoRightMerge
+ cmp ptr3+1
+ bne NoRightMerge
+
+; Merge with the right block. Do f->size += right->size;
+
+ ldy #size
+ lda ptr1
+ add (ptr3),y
+ sta (ptr2),y
+ iny ; Points to size+1
+ lda ptr1+1
+ adc (ptr3),y
+ sta (ptr2),y
+
+; Set f->next = right->next and remember f->next in ptr1 (we don't need the
+; size stored there any longer)
+
+ iny ; Points to next
+ lda (ptr3),y ; Low byte of right->next
+ sta (ptr2),y ; Store to low byte of f->next
+ sta ptr1
+ iny ; Points to next+1
+ lda (ptr3),y ; High byte of right->next
+ sta (ptr2),y ; Store to high byte of f->next
+ sta ptr1+1
+ ora ptr1
+ beq @L1 ; Jump if f->next zero
+
+; f->next->prev = f;
+
+ iny ; Points to prev
+ lda ptr2 ; Low byte of f
+ sta (ptr1),y ; Low byte of f->next->prev
+ iny ; Points to prev+1
+ lda ptr2+1 ; High byte of f
+ sta (ptr1),y ; High byte of f->next->prev
+ jmp CheckLeftMerge ; Done
+
+; f->next is zero, this is now the last block
+
+@L1: lda ptr2 ; _hlast = f;
+ sta __hlast
+ lda ptr2+1
+ sta __hlast+1
+ jmp CheckLeftMerge
+
+; No right merge, just set the link.
+
+NoRightMerge:
+ ldy #next ; f->next = right;
+ lda ptr3
+ sta (ptr2),y
+ iny ; Points to next+1
+ lda ptr3+1
+ sta (ptr2),y
+
+ iny ; Points to prev
+ lda ptr2 ; right->prev = f;
+ sta (ptr3),y
+ iny ; Points to prev+1
+ lda ptr2+1
+ sta (ptr3),y
+
+; Check if the left pointer is zero
+
+CheckLeftMerge:
+ lda ptr4 ; left == NULL?
+ ora ptr4+1
+ bne CheckLeftMerge2 ; Jump if there is a left block
+
+; We don't have a left block, so f is actually the new freelist start
+
+ ldy #prev
+ sta (ptr2),y ; f->prev = 0;
+ iny
+ sta (ptr2),y
+
+ lda ptr2 ; _hfirst = f;
+ sta __hfirst
+ lda ptr2+1
+ sta __hfirst+1
+
+ rts ; Done
+
+; Check if the left block is adjacent to the following one
+
+CheckLeftMerge2:
+ ldy #size ; Calculate left + left->size
+ lda (ptr4),y ; Low byte of left->size
+ add ptr4
+ tax
+ iny ; Points to size+1
+ lda (ptr4),y ; High byte of left->size
+ adc ptr4+1
+
+ cpx ptr2
+ bne NoLeftMerge
+ cmp ptr2+1
+ bne NoLeftMerge ; Jump if blocks not adjacent
+
+; Merge with the left block. Do left->size += f->size;
+
+ dey ; Points to size
+ lda (ptr4),y
+ add (ptr2),y
+ sta (ptr4),y
+ iny ; Points to size+1
+ lda (ptr4),y
+ adc (ptr2),y
+ sta (ptr4),y
+
+; Set left->next = f->next and remember left->next in ptr1.
+
+ iny ; Points to next
+ lda (ptr2),y ; Low byte of f->next
+ sta (ptr4),y
+ sta ptr1
+ iny ; Points to next+1
+ lda (ptr2),y ; High byte of f->next
+ sta (ptr4),y
+ sta ptr1+1
+ ora ptr1 ; left->next == NULL?
+ beq @L1
+
+; Do left->next->prev = left
+
+ iny ; Points to prev
+ lda ptr4 ; Low byte of left
+ sta (ptr1),y
+ iny
+ lda ptr4+1 ; High byte of left
+ sta (ptr1),y
+ rts ; Done
+
+; This is now the last block, do _hlast = left
+
+@L1: lda ptr4
+ sta __hlast
+ lda ptr4+1
+ sta __hlast+1
+ rts ; Done
+
+; No merge of the left block, just set the link. Y points to size+1 if
+; we come here. Do left->next = f.
+
+NoLeftMerge:
+ iny ; Points to next
+ lda ptr2 ; Low byte of left
+ sta (ptr4),y
+ iny
+ lda ptr2+1 ; High byte of left
+ sta (ptr4),y
+
+; Do f->prev = left
+
+ iny ; Points to prev
+ lda ptr4
+ sta (ptr2),y
+ iny
+ lda ptr4+1
+ sta (ptr2),y
+ rts ; Done
-; The block is not on top of the heap. Add it to the free list.
-@AddToFreeList:
- lda ptr1
- ldx ptr1+1
- jsr pushax ; Push b
- lda ptr2
- ldx ptr2+1
- jsr pushax ; Push size
- jmp __hadd ; Add to free list and return
-
projects / cc65 / blobdiff