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z80_unpacker: optimisations: -3B and ~-24T in decode_bit = 177B

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Peter Helcmanovsky (Ped)
2022-09-14 23:48:59 +02:00
parent 6624940ed9
commit aa3fad4d80
1 changed files with 3 additions and 6 deletions
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9
z80_unpacker/unpack.asm
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@@ -210,7 +210,6 @@ decode_bit:
push bc
ld c,l ; C = (upkr_state & 255); (preserving the value)
push af
push af
jr nc,.bit_is_0
neg ; A = -prob == (256-prob), CF=1 preserved
.bit_is_0:
@@ -226,16 +225,14 @@ decode_bit:
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
ld d,-16 ; D = -prob_offset (-16 0xF0 when bit = 0)
jr nc,.bit_is_0_2
ld d,b ; D = -prob_offset (0 when bit = 1) (also does fix following ADD)
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
jr c,.bit_is_1
ld d,-16 ; 0xF0
.bit_is_1: ; D:E = -prob_offset:prob, A = prob
ld e,a ; D:E = -prob_offset:prob, A = prob
and $F8
rra
rra