From db1c7d2d14c11631e7113621f56a2d88e1b8b36e Mon Sep 17 00:00:00 2001
From: "Peter Helcmanovsky (Ped)" <ped@7gods.org>
Date: Mon, 19 Sep 2022 11:49:53 +0200
Subject: [PATCH] z80_unpacker: optimisation: -1B in decode_number (fwd 171B /
 rev 168B)

---
 z80_unpacker/example/example.sna | Bin 49179 -> 49179 bytes
 z80_unpacker/unpack.asm          |   9 +++++----
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/z80_unpacker/example/example.sna b/z80_unpacker/example/example.sna
index 608c82a0cd10aa8ef47756414fd76847ca067304..e3e730a6542a30c1ad427059d407fb98c5464bff 100644
GIT binary patch
delta 167
zcmbQ;z&yKwd4u>u#<P<p7Fq-pJ+u(uIa~Dbw4lMy%9}#MHv=SIR<P{4QuNS(`|Os7
z(p8&JybVr!$R`ivT)ml;&B(y;*6HBe4L1V>4)R<*U85kt(XPODw~pbia{t?`PZg8r
zFEr+5KU?_lwA5*7AZ77o^23D=qWq75Cd53tdQ*{sLGs|+9YF0zcqW@Jas#TBd<0f2
S`N-nS=B`DrWF{BwUkL!@3s7YM

delta 165
zcmbQ;z&yKwd4u>u#&eS;7FzfhKC}?vIa~Pfw4lMy%9}#MHv=SIR<P{4Quxq-`|Re2
z(p8&JybVr!$R`ivT)ml;&B(y;*6HBe4L1V>4qiQ7qaeW1uE2J;j^VCy|J$rj<&zgI
zH0I|38z^;J8bn)sn*3m)1EauX#YMuCO&7U|17)Qiod(NFJ+k;@4`N#UJh@Tvm-t45
L7c7%Y_Adtj`%g_n

diff --git a/z80_unpacker/unpack.asm b/z80_unpacker/unpack.asm
index a2d1fc9..4cd5829 100644
--- a/z80_unpacker/unpack.asm
+++ b/z80_unpacker/unpack.asm
@@ -187,6 +187,9 @@ int upkr_decode_bit(int context_index) {
     return bit;
 }
 */
+inc_c_decode_bit:
+  ; ++low(context_index) before decode_bit (to get -1B by two calls in decode_number)
+    inc     c
 decode_bit:
   ; HL = upkr_state
   ; IX = upkr_data_ptr
@@ -298,13 +301,11 @@ decode_number:
     ld      de,$7FFF            ; length = 0 with positional-stop-bit
     jr      .loop_entry
 .loop:
-    inc     c                   ; context_index + 1
-    call    decode_bit
+    call    inc_c_decode_bit    ; context_index + 1
     rr      d
     rr      e                   ; DE = length = (length >> 1) | (bit << 15);
 .loop_entry:
-    inc     c                   ; context_index += 2
-    call    decode_bit
+    call    inc_c_decode_bit    ; context_index += 2
     jr      c,.loop
 .fix_bit_pos:
     ccf                         ; NC will become this final `| (1 << bit_pos)` bit