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;
; Ullrich von Bassewitz, 2004-07-17
;
; size_t __fastcall__ _heapblocksize (const void* ptr);
;
; Return the size of an allocated block.
;
.importzp ptr1, ptr2
.export __heapblocksize
.include "_heap.inc"
.macpack generic
.macpack cpu
;-----------------------------------------------------------------------------
; Code
__heapblocksize:
; Below the user data is a pointer that points to the start of the real
; (raw) memory block. The first word of this block is the size. To access
; the raw block pointer, we will decrement the high byte of the pointer,
; the pointer is then at offset 254/255.
sta ptr1
dex
stx ptr1+1
ldy #$FE
lda (ptr1),y
sta ptr2 ; Place the raw block pointer into ptr2
iny
lda (ptr1),y
sta ptr2+1
; Load the size from the raw block
ldy #usedblock::size+1
lda (ptr2),y
tax
.if (.cpu .bitand CPU_ISET_65SC02)
lda (ptr2)
.else
dey
lda (ptr2),y
.endif
; Correct the raw block size so that is shows the user visible portion. To
; do that, we must decrease the size by the amount of unused memory, which is
; the difference between the user space pointer and the raw memory block
; pointer. Since we have decremented the user space pointer by 256, we will
; have to correct the result.
;
; return size - (ptr1 + 256 - ptr2)
; return size - ptr1 - 256 + ptr2
dex ; - 256
add ptr2
pha
txa
adc ptr2+1
tax
pla
sub ptr1
pha
txa
sbc ptr1+1
tax
pla
; Done
rts
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