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z80_unpacker: optimisations: -1B in unpack implementation = 182B

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Peter Helcmanovsky (Ped)
2022-09-14 20:14:13 +02:00
parent a75a35efb2
commit c3a9773e5c
1 changed files with 6 additions and 5 deletions
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11
z80_unpacker/unpack.asm
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@@ -84,8 +84,8 @@ unpack:
; BC = probs (context_index 0), state HL = 0, A' = 0x80 (no source bits left in upkr_current_byte) ; BC = probs (context_index 0), state HL = 0, A' = 0x80 (no source bits left in upkr_current_byte)
; ** main loop to decompress data ; ** main loop to decompress data
.decompress_data_reset_match: ; D = prev_was_match = uninitialised, literal is expected first => will reset D to "false"
ld d,0 ; prev_was_match = 0; ; values for false/true of prev_was_match are: false = high(probs), true = 1 + high(probs)
.decompress_data: .decompress_data:
ld c,0 ld c,0
call decode_bit ; if(upkr_decode_bit(0)) call decode_bit ; if(upkr_decode_bit(0))
@@ -102,16 +102,17 @@ unpack:
ld (de),a ; *write_ptr++ = byte; ld (de),a ; *write_ptr++ = byte;
inc de inc de
exx exx
jr .decompress_data_reset_match ld d,b ; prev_was_match = false
jr .decompress_data
; * copy chunk of already decompressed data (match) ; * copy chunk of already decompressed data (match)
.copy_chunk: .copy_chunk:
ld a,b
inc b ; context_index = 256 inc b ; context_index = 256
; if(prev_was_match || upkr_decode_bit(256)) { ; if(prev_was_match || upkr_decode_bit(256)) {
; offset = upkr_decode_length(257) - 1; ; offset = upkr_decode_length(257) - 1;
; if (0 == offset) break; ; if (0 == offset) break;
; } ; }
xor a
cp d ; CF = prev_was_match cp d ; CF = prev_was_match
call nc,decode_bit ; if not prev_was_match, then upkr_decode_bit(256) call nc,decode_bit ; if not prev_was_match, then upkr_decode_bit(256)
jr nc,.keep_offset ; if neither, keep old offset jr nc,.keep_offset ; if neither, keep old offset
@@ -140,7 +141,7 @@ unpack:
pop bc ; BC = length pop bc ; BC = length
ldir ldir
exx exx
ld d,b ; prev_was_match = non-zero ld d,b ; prev_was_match = true
djnz .decompress_data ; adjust context_index back to 0..255 range, go to main loop djnz .decompress_data ; adjust context_index back to 0..255 range, go to main loop
/* /*