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z80_unpacker: add backward variant of unpacker + example extended

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This commit is contained in:
Peter Helcmanovsky (Ped)
2022-09-18 00:23:14 +02:00
parent 3c773aca8d
commit b13fa05413
7 changed files with 80 additions and 21 deletions
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24
z80_unpacker/unpack.asm
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@@ -15,6 +15,10 @@
;; modifies: all registers except IY, requires 10 bytes of stack space
;;
; DEFINE BACKWARDS_UNPACK ; uncomment to build backwards depacker
; initial IX points at last byte of compressed data
; initial DE' points at last byte of unpacked data
; DEFINE UPKR_UNPACK_SPEED ; uncomment to get larger but faster unpack routine
OPT push reset --syntax=abf
@@ -102,7 +106,7 @@ unpack:
ld a,c
exx
ld (de),a ; *write_ptr++ = byte;
inc de
IFNDEF BACKWARDS_UNPACK : inc de : ELSE : dec de : ENDIF
exx
ld d,b ; prev_was_match = false
jr .decompress_data
@@ -139,9 +143,13 @@ unpack:
ld h,d ; DE = write_ptr
ld l,e
.offset+*: ld bc,0
IFNDEF BACKWARDS_UNPACK
sbc hl,bc ; CF=0 from decode_number ; HL = write_ptr - offset
ELSE
add hl,bc ; HL = write_ptr + offset
ENDIF
pop bc ; BC = length
ldir
IFNDEF BACKWARDS_UNPACK : ldir : ELSE : lddr : ENDIF
exx
ld d,b ; prev_was_match = true
djnz .decompress_data ; adjust context_index back to 0..255 range, go to main loop
@@ -195,7 +203,7 @@ decode_bit:
jr nz,.has_bit ; CF=data, ZF=0 -> some bits + stop bit still available
; CF=1 (by stop bit)
ld a,(ix)
inc ix ; upkr_current_byte = *upkr_data_ptr++;
IFNDEF BACKWARDS_UNPACK : inc ix : ELSE : dec ix : ENDIF ; upkr_current_byte = *upkr_data_ptr++;
adc a,a ; CF=data, b0=1 as new stop bit
.has_bit:
adc hl,hl ; upkr_state = (upkr_state << 1) + (upkr_current_byte >> 7);
@@ -306,12 +314,12 @@ decode_number:
; 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
ORG UPKR_PROBS_ORIGIN
probs: EQU ((UPKR_PROBS_ORIGIN) + 255) & -$100 ; probs array aligned to 256
ELSE
probs: EQU ($ + 255) & -$100 ; probs array aligned to 256
ENDIF
probs: EQU ($+255) & -$100 ; probs array aligned to 256
.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)
.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