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z80_unpacker: comment with possible LUT variant of updating probs value

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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.
This commit is contained in:
Peter Helcmanovsky (Ped)
2022-09-19 14:31:00 +02:00
parent a8fd3dc573
commit 9913dcf4bb
1 changed files with 29 additions and 14 deletions
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43
z80_unpacker/unpack.asm
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@@ -316,6 +316,21 @@ decode_number:
jr c,.fix_bit_pos ; until stop bit is reached (all bits did land to correct position) 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) 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) & -$100 ; probs array aligned to 256
ENDIF
.real_c: EQU 1 + 255 + 1 + 2*NUMBER_BITS ; real size of probs array
.c: EQU (.real_c + 1) & -2 ; padding to even size (required by init code)
.e: EQU probs + .c
DISPLAY "upkr.unpack probs array placed at: ",/A,probs,",\tsize: ",/A,probs.c
/* /*
archived: negligibly faster but +6B longer decode_number variant using HL' and BC' to archived: negligibly faster but +6B longer decode_number variant using HL' and BC' to
do `number|=(1<<bit_pos);` type of logic in single loop. do `number|=(1<<bit_pos);` type of logic in single loop.
@@ -347,20 +362,20 @@ decode_number:
; pop de ; pop de
; ret ; ret
DISPLAY "upkr.unpack total size: ",/D,$-unpack /*
archived: possible LUT variant of updating probs value, requires 512-aligned 512B table (not tested)
; reserve space for probs array without emitting any machine code (using only EQU) */
; code is replacing decode_bit from "; *** adjust probs[context_index]", followed by `ld (bc),a : add a,d ...`
IFDEF UPKR_PROBS_ORIGIN ; if specific address is defined by user, move probs array there ; ld c,a
probs: EQU ((UPKR_PROBS_ORIGIN) + 255) & -$100 ; probs array aligned to 256 ; ld a,high(probs_update_table)/2 ; must be 512 aligned
ELSE ; rla
probs: EQU ($ + 255) & -$100 ; probs array aligned to 256 ; ld b,a
ENDIF ; ld a,(bc)
.real_c: EQU 1 + 255 + 1 + 2*NUMBER_BITS ; real size of probs array ; pop bc
.c: EQU (.real_c + 1) & -2 ; padding to even size (required by init code) ; -------------------------------------------
.e: EQU probs + .c ; probs_update_table: EQU probs-512
; -------------------------------------------
DISPLAY "upkr.unpack probs array placed at: ",/A,probs,",\tsize: ",/A,probs.c ; table generator is not obvious and probably not short either, 20+ bytes almost for sure, maybe even 30-40
ENDMODULE ENDMODULE
OPT pop OPT pop