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colinleroycolinleroy
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Rewrite realloc in asm
-80 bytes, -39% cycles
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2 files changed

+213
-114
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2 files changed

+213
-114
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‎libsrc/common/realloc.c

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This file was deleted.

‎libsrc/common/realloc.s

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;
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; Colin Leroy-Mira, 2024
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;
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; void* __fastcall__ realloc (void* block, register size_t size)
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;
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.importzp ptr1, ptr2, ptr3, ptr4, tmp1, tmp2, tmp3, tmp4, sp
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.import _malloc, _memcpy, _free
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.import pushax, popptr1, return0
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.import incsp2, decsp2
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.export _realloc
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.include "_heap.inc"
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.macpack generic
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;----------------------------------------------------------------------------
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; Aliases for clarity
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block = ptr1
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size = ptr2
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ublock = ptr3
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oldsize = ptr4
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newblock = tmp1 ; (and tmp2)
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orgblock = tmp3 ; (and tmp4)
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;----------------------------------------------------------------------------
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; Code
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_realloc:
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sta size ; Store size
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stx size+1
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jsr popptr1 ; Pop block
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lda block+1 ; Is block null?
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tax
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ora block
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bne :+
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lda size ; Block is null, just malloc
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ldx size+1
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jmp _malloc
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: lda size ; Is size 0?
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ora size+1
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bne :+
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lda block ; It is: free block (high byte already in X)
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jsr _free
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jmp return0
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: clc ; Add internal used size
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lda size
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adc #HEAP_ADMIN_SPACE
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sta size
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bcc :+
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inc size+1
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bne :+
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lda #$00 ; Size high byte now 0: We overflowed!
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tax
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rts
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: ldx size+1 ; Should we round size up?
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bne :+
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cmp #.sizeof (freeblock)
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bcs :+
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lda #.sizeof (freeblock)
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sta size ; (we presuppose that sizeof (freeblock) is < 256)
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: lda block ; Get pointer to raw memory block
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sta orgblock ; Store original pointer
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sec
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sbc #.sizeof(usedblock)
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sta ublock
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lda block+1
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sta orgblock+1 ; Finish storing original pointer
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sbc #0
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sta ublock+1 ; We have our usedblock struct
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; Get block start
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ldy #usedblock::start+1
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lda (ublock),y
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tax ; Backup ublock high
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dey
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lda (ublock),y
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sta ublock ; Store ublock
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stx ublock+1
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; Remember oldsize
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ldy #usedblock::size+1
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lda (ublock),y
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sta oldsize+1
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dey
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lda (ublock),y
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sta oldsize
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clc ; Is the block at heap top?
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adc ublock
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tay
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lda ublock+1
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adc oldsize+1
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cmp ___heapptr+1
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bne must_malloc_new
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cpy ___heapptr
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bne must_malloc_new
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tya ; Put ___heapptr back in A
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sec ; Check if we have enough memory at heap top
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sbc oldsize ; Substract oldsize
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sta newblock
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lda ___heapptr+1
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sbc oldsize+1
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sta newblock+1
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clc
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lda newblock ; And add size
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adc size
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sta newblock
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lda newblock+1
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adc size+1
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sta newblock+1
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bcs must_malloc_new ; If we have a carry there we overflowed
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cmp ___heapend+1
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bne :+
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lda newblock
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cmp ___heapend
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: bcc :+
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bne must_malloc_new
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: lda newblock ; There is enough space
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sta ___heapptr ; Update heapptr
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lda newblock+1
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sta ___heapptr+1
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ldy #usedblock::start+1
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lda ublock+1
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sta (ublock),y ; Update block start
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dey
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lda ublock
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sta (ublock),y
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dey
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.assert usedblock::size = usedblock::start-2, error
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lda size+1
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sta (ublock),y ; Update block size
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dey
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lda size
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sta (ublock),y
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lda orgblock ; Return original block
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ldx orgblock+1
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rts
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must_malloc_new: ; The block is not at heap top, or too big
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lda size+1
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pha ; Backup new size (at this point the only ptr
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tax ; we'll need after malloc). tmp* are safe
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lda size ; from malloc, memcpy and free.
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pha
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jsr _malloc
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cmp #$00 ; Did malloc succeed?
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bne :+
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cpx #$00
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bne :+
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pla ; Pop size backup and return NULL
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pla
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txa ; X already 0
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rts ; No
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: sta newblock ; Yes, store newblock
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stx newblock+1
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jsr pushax ; Push newblock for memcpy
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lda orgblock ; Push orgblock for memcpy
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ldx orgblock+1
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jsr pushax
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sec ; Remove admin space from oldsize
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lda oldsize
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sbc #<HEAP_ADMIN_SPACE
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sta oldsize
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lda oldsize+1
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sbc #>HEAP_ADMIN_SPACE
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sta oldsize+1
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pla ; Restore new size to AX
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tay
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pla
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tax
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tya
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cmp oldsize ; Find the smallest size
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bcc :+
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cpx oldsize+1
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bcc :+
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lda oldsize
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ldx oldsize+1
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: jsr _memcpy ; And copy data
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lda orgblock ; Free old block
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ldx orgblock+1
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jsr _free
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lda newblock ; Return new block
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ldx newblock+1
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rts

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