From 9913dcf4bb77e5ef5a4a9591a915a063f07a8af6 Mon Sep 17 00:00:00 2001
From: "Peter Helcmanovsky (Ped)" <ped@7gods.org>
Date: Mon, 19 Sep 2022 14:31:00 +0200
Subject: [PATCH] z80_unpacker: comment with possible LUT variant of updating
 probs value

missing 512 byte table generator, which doesn't look trivial to do
(especially in terms of code size).
Not tested, but looks as decent speed up.
---
 z80_unpacker/unpack.asm | 43 +++++++++++++++++++++++++++--------------
 1 file changed, 29 insertions(+), 14 deletions(-)

diff --git a/z80_unpacker/unpack.asm b/z80_unpacker/unpack.asm
index 300579d..e0218e9 100644
--- a/z80_unpacker/unpack.asm
+++ b/z80_unpacker/unpack.asm
@@ -316,6 +316,21 @@ decode_number:
     jr      c,.fix_bit_pos      ; until stop bit is reached (all bits did land to correct position)
     ret                         ; return with CF=0 (important for unpack routine)
 
+    DISPLAY "upkr.unpack total size: ",/D,$-unpack
+
+    ; reserve space for probs array without emitting any machine code (using only EQU)
+
+    IFDEF UPKR_PROBS_ORIGIN     ; if specific address is defined by user, move probs array there
+probs:      EQU ((UPKR_PROBS_ORIGIN) + 255) & -$100     ; probs array aligned to 256
+    ELSE
+probs:      EQU ($ + 255) & -$100                       ; probs array aligned to 256
+    ENDIF
+.real_c:    EQU 1 + 255 + 1 + 2*NUMBER_BITS             ; real size of probs array
+.c:         EQU (.real_c + 1) & -2                      ; padding to even size (required by init code)
+.e:         EQU probs + .c
+
+    DISPLAY "upkr.unpack probs array placed at: ",/A,probs,",\tsize: ",/A,probs.c
+
 /*
  archived: negligibly faster but +6B longer decode_number variant using HL' and BC' to
  do `number|=(1<<bit_pos);` type of logic in single loop.
@@ -347,20 +362,20 @@ decode_number:
 ;     pop     de
 ;     ret
 
-    DISPLAY "upkr.unpack total size: ",/D,$-unpack
-
-    ; reserve space for probs array without emitting any machine code (using only EQU)
-
-    IFDEF UPKR_PROBS_ORIGIN     ; if specific address is defined by user, move probs array there
-probs:      EQU ((UPKR_PROBS_ORIGIN) + 255) & -$100     ; probs array aligned to 256
-    ELSE
-probs:      EQU ($ + 255) & -$100                       ; probs array aligned to 256
-    ENDIF
-.real_c:    EQU 1 + 255 + 1 + 2*NUMBER_BITS             ; real size of probs array
-.c:         EQU (.real_c + 1) & -2                      ; padding to even size (required by init code)
-.e:         EQU probs + .c
-
-    DISPLAY "upkr.unpack probs array placed at: ",/A,probs,",\tsize: ",/A,probs.c
+/*
+ archived: possible LUT variant of updating probs value, requires 512-aligned 512B table (not tested)
+*/
+; code is replacing decode_bit from "; *** adjust probs[context_index]", followed by `ld (bc),a : add a,d ...`
+;     ld      c,a
+;     ld      a,high(probs_update_table)/2    ; must be 512 aligned
+;     rla
+;     ld      b,a
+;     ld      a,(bc)
+;     pop     bc
+; -------------------------------------------
+; probs_update_table: EQU probs-512
+; -------------------------------------------
+; table generator is not obvious and probably not short either, 20+ bytes almost for sure, maybe even 30-40
 
     ENDMODULE
     OPT pop