From a8fd3dc5732a8ffe2a22948194dfea982a9ca643 Mon Sep 17 00:00:00 2001
From: "Peter Helcmanovsky (Ped)" <ped@7gods.org>
Date: Mon, 19 Sep 2022 13:20:44 +0200
Subject: [PATCH] z80_unpacker: optimisation: -1B in decode_number (fwd 170B /
 rev 167B)

slightly slower code, ROM unpack is back to ~22.6s
---
 z80_unpacker/example/example.sna | Bin 49179 -> 49179 bytes
 z80_unpacker/unpack.asm          |   7 +++----
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/z80_unpacker/example/example.sna b/z80_unpacker/example/example.sna
index e3e730a6542a30c1ad427059d407fb98c5464bff..5a56975f125af16b3553eae3b10735738c65bc0f 100644
GIT binary patch
delta 113
zcmV-%0FM8gfCHO=1F#pN0nC#ap}7P9x7?G}p(ZOC;y4ft%^Bj$5it3A*%BMsP#EcW
z1iI82;xG%%TjCpfv&ijJ4&n|U&0CWuq9Fnw;*+7FFc$x}+!*4^8p|8a7~(keKg$}+
T8#wvNu_5{wu`uielXSnQujDop

delta 115
zcmbQ;z&yKwd4u>u#<P<p7Vc!Jmta3T`N~2yZK+2V0z7A>9-S66_*r>VNcv`g#LEhn
zU00+Y8E~JCc_dx6`NZ2`{zrWBXJaO-E>dJtcr<z8LIZJ-e#u9trA|u&DT^=mAeP0?
SlN%L(iElJ`#WJ~M|8f9E%rngZ

diff --git a/z80_unpacker/unpack.asm b/z80_unpacker/unpack.asm
index b3c48ea..300579d 100644
--- a/z80_unpacker/unpack.asm
+++ b/z80_unpacker/unpack.asm
@@ -301,13 +301,12 @@ decode_number:
   ; BC = probs+context_index-1
   ; A' = upkr_current_byte (!!! init to 0x80 at start, not 0x00)
   ; return length in DE, CF=0
-    ld      de,$7FFF            ; length = 0 with positional-stop-bit
-    jr      .loop_entry
+    ld      de,$FFFF            ; length = 0 with positional-stop-bit
+    or      a                   ; CF=0 to skip getting data bit and use only `rr d : rr e` to fix init DE
 .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      e                   ; DE = length = (length >> 1) | (bit << 15);
-.loop_entry:
     call    inc_c_decode_bit    ; context_index += 2
     jr      c,.loop
 .fix_bit_pos: