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z80_unpacker: optimisation: -1B in decode_number (fwd 170B / rev 167B)

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slightly slower code, ROM unpack is back to ~22.6s
This commit is contained in:
Peter Helcmanovsky (Ped)
2022-09-19 13:20:44 +02:00
parent e1f9fa143a
commit a8fd3dc573
2 changed files with 3 additions and 4 deletions
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z80_unpacker/example/example.sna
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z80_unpacker/unpack.asm
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@@ -301,13 +301,12 @@ decode_number:
; BC = probs+context_index-1 ; BC = probs+context_index-1
; A' = upkr_current_byte (!!! init to 0x80 at start, not 0x00) ; A' = upkr_current_byte (!!! init to 0x80 at start, not 0x00)
; return length in DE, CF=0 ; return length in DE, CF=0
ld de,$7FFF ; length = 0 with positional-stop-bit ld de,$FFFF ; length = 0 with positional-stop-bit
jr .loop_entry or a ; CF=0 to skip getting data bit and use only `rr d : rr e` to fix init DE
.loop: .loop:
call inc_c_decode_bit ; context_index + 1 call c,inc_c_decode_bit ; get data bit, context_index + 1 / if CF=0 just add stop bit into DE init
rr d rr d
rr e ; DE = length = (length >> 1) | (bit << 15); rr e ; DE = length = (length >> 1) | (bit << 15);
.loop_entry:
call inc_c_decode_bit ; context_index += 2 call inc_c_decode_bit ; context_index += 2
jr c,.loop jr c,.loop
.fix_bit_pos: .fix_bit_pos: