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z80_unpacker: optimisations: -1B by keeping write_ptr in DE'

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This commit is contained in:
Peter Helcmanovsky (Ped)
2022-09-13 23:57:59 +02:00
parent 919a892ef0
commit d30baaa91f
2 changed files with 11 additions and 12 deletions
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4
z80_unpacker/example/example.asm
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@@ -24,9 +24,9 @@ start:
ldi a,(ix) ; fake: ld a,(ix) : inc ix
out (254),a
; call unpack of next image directly into VRAM
ld hl,$4000 ; target VRAM
ld de,$4000 ; target VRAM
exx
; IX = packed data, HL' = destination ($4000)
; IX = packed data, DE' = destination ($4000)
; returned IX will point right after the packed data
call upkr.unpack
; do some busy loop with CPU to delay between images

19
z80_unpacker/unpack.asm
View File

@@ -10,7 +10,7 @@
;; public API:
;;
;; upkr.unpack
;; IN: IX = packed data, HL' (shadow HL) = destination
;; IN: IX = packed data, DE' (shadow DE) = destination
;; OUT: IX = after packed data
;; modifies: all registers except IY, requires 14 bytes of stack space
;;
@@ -64,7 +64,7 @@ int upkr_unpack(void* destination, void* compressed_data) {
return write_ptr - (u8*)destination;
}
*/
; IN: IX = compressed_data, HL' = destination
; IN: IX = compressed_data, DE' = destination
unpack:
; ** reset probs to 0x80, also reset HL (state) to zero, and set BC to probs+context 0
ld hl,probs.c>>1
@@ -97,8 +97,8 @@ unpack:
jr nc,.decode_byte ; while(byte < 256)
ld a,e
exx
ld (hl),a ; *write_ptr++ = byte;
inc hl
ld (de),a ; *write_ptr++ = byte;
inc de
exx
jr .decompress_data_reset_match
@@ -133,13 +133,12 @@ unpack:
call decode_length ; length = upkr_decode_length(257 + 64);
push de
exx
push hl
.offset+*: ld de,0
sbc hl,de ; CF=0 from decode_length
pop de
pop bc
ld h,d ; DE = write_ptr
ld l,e
.offset+*: ld bc,0
sbc hl,bc ; CF=0 from decode_length ; HL = write_ptr - offset
pop bc ; BC = length
ldir
ex de,hl
exx
ld d,b ; prev_was_match = non-zero
djnz .decompress_data ; adjust context_index back to 0..255 range, go to main loop