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cc65/libsrc/common/malloc.s
cuz 581c12ce40 Move _heap.h to the compiler include dir. 
Create heap.inc and use that from the assembler code.
Rename heap related _h... variables to _heap...
Add _heapmaxavail and _heapmemavail functions.


git-svn-id: svn://svn.cc65.org/cc65/trunk@1912 b7a2c559-68d2-44c3-8de9-860c34a00d81
2003-02-01 12:22:09 +00:00

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