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z80_unpacker: add performance variant of depacker

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Peter Helcmanovsky (Ped)
2022-09-16 02:50:23 +02:00
parent a5406deb30
commit 3c773aca8d
1 changed files with 19 additions and 0 deletions
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19
z80_unpacker/unpack.asm
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@@ -15,6 +15,8 @@
;; modifies: all registers except IY, requires 10 bytes of stack space ;; modifies: all registers except IY, requires 10 bytes of stack space
;; ;;
; DEFINE UPKR_UNPACK_SPEED ; uncomment to get larger but faster unpack routine
OPT push reset --syntax=abf OPT push reset --syntax=abf
MODULE upkr MODULE upkr
@@ -215,6 +217,10 @@ decode_bit:
ld d,0 ld d,0
ld e,a ; DE = state_scale ; prob || (256-prob) ld e,a ; DE = state_scale ; prob || (256-prob)
ld l,d ; H:L = (upkr_state>>8) : 0 ld l,d ; H:L = (upkr_state>>8) : 0
IFNDEF UPKR_UNPACK_SPEED
;; looped MUL for minimum unpack size
ld b,8 ; counter ld b,8 ; counter
.mulLoop: .mulLoop:
add hl,hl add hl,hl
@@ -222,6 +228,19 @@ decode_bit:
add hl,de add hl,de
.mul0: .mul0:
djnz .mulLoop ; until HL = state_scale * (upkr_state>>8), also BC becomes (upkr_state & 255) djnz .mulLoop ; until HL = state_scale * (upkr_state>>8), also BC becomes (upkr_state & 255)
ELSE
;;; unrolled MUL for better performance, +25 bytes unpack size
ld b,d
DUP 8
add hl,hl
jr nc,000_f
add hl,de
000:
EDUP
ENDIF
add hl,bc ; HL = state_scale * (upkr_state >> 8) + (upkr_state & 255) add hl,bc ; HL = state_scale * (upkr_state >> 8) + (upkr_state & 255)
pop af pop af
ld d,-16 ; D = -prob_offset (-16 0xF0 when bit = 0) ld d,-16 ; D = -prob_offset (-16 0xF0 when bit = 0)