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z80_unpacker: optimisations: -2B and -27T in decode_bit = 180B

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Peter Helcmanovsky (Ped)
2022-09-14 23:17:07 +02:00
parent c3a9773e5c
commit 6624940ed9
1 changed files with 9 additions and 10 deletions
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19
z80_unpacker/unpack.asm
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@@ -207,8 +207,9 @@ decode_bit:
inc a
; ** adjust state
push af
push bc
ld c,l ; C = (upkr_state & 255); (preserving the value)
push af
push hl
push af
jr nc,.bit_is_0
neg ; A = -prob == (256-prob), CF=1 preserved
@@ -216,22 +217,19 @@ decode_bit:
ld d,0
ld e,a ; DE = state_scale ; prob || (256-prob)
ld l,d ; H:L = (upkr_state>>8) : 0
ld a,8 ; counter
ld b,8 ; counter
.mulLoop:
add hl,hl
jr nc,.mul0
add hl,de
.mul0:
dec a
jr nz,.mulLoop ; until HL = state_scale * (upkr_state>>8)
djnz .mulLoop ; until HL = state_scale * (upkr_state>>8), also BC becomes (upkr_state & 255)
add hl,bc ; HL = state_scale * (upkr_state >> 8) + (upkr_state & 255)
pop af
jr nc,.bit_is_0_2
dec d ; D = 0xFF (DE = -prob)
add hl,de ; HL += -prob
.bit_is_0_2: ; HL = state_offset + state_scale * (upkr_state >> 8)
pop de
ld d,0 ; DE = (upkr_state & 255)
add hl,de ; HL = state_offset + state_scale * (upkr_state >> 8) + (upkr_state & 255) ; new upkr_state
dec h
add hl,de ; HL += -prob (HL += (256 - prob) - 256)
.bit_is_0_2: ; HL = state_offset + state_scale * (upkr_state >> 8) + (upkr_state & 255) ; new upkr_state
; *** adjust probs[context_index]
pop af ; restore prob and bit
ld e,a
@@ -246,6 +244,7 @@ decode_bit:
adc a,d ; A = -prob_offset + ((prob + 8) >> 4)
neg
add a,e ; A = prob_offset + prob - ((prob + 8) >> 4)
pop bc
ld (bc),a ; update probs[context_index]
pop af ; restore resulting CF = bit
pop de