diff options
| author | Juan J. Martinez <jjm@usebox.net> | 2022-09-06 07:37:20 +0100 |
|---|---|---|
| committer | Juan J. Martinez <jjm@usebox.net> | 2022-09-06 07:37:20 +0100 |
| commit | 30bf0f51335e87812ffeb54e9437f0b6a1514d67 (patch) | |
| tree | 9c85a2de53b4da69fcfaa84488cc6c12ebd3e5d0 /tools/rasm/decrunch/dzx0_standard_back.asm | |
| parent | d8990284057e6401d0374f439df51879595d804d (diff) | |
| download | ubox-msx-lib-30bf0f51335e87812ffeb54e9437f0b6a1514d67.tar.gz ubox-msx-lib-30bf0f51335e87812ffeb54e9437f0b6a1514d67.zip | |
Updated rasm to 1.7
Diffstat (limited to 'tools/rasm/decrunch/dzx0_standard_back.asm')
| -rw-r--r-- | tools/rasm/decrunch/dzx0_standard_back.asm | 65 |
1 files changed, 65 insertions, 0 deletions
diff --git a/tools/rasm/decrunch/dzx0_standard_back.asm b/tools/rasm/decrunch/dzx0_standard_back.asm new file mode 100644 index 0000000..3da94bd --- /dev/null +++ b/tools/rasm/decrunch/dzx0_standard_back.asm @@ -0,0 +1,65 @@ +; ----------------------------------------------------------------------------- +; ZX0 decoder by Einar Saukas +; "Standard" version (69 bytes only) - BACKWARDS VARIANT +; ----------------------------------------------------------------------------- +; Parameters: +; HL: last source address (compressed data) +; DE: last destination address (decompressing) +; ----------------------------------------------------------------------------- + +Macro dzx0_standard_back + ld bc, 1 ; preserve default offset 1 + push bc + ld a, $80 +@dzx0sb_literals: + call @dzx0sb_elias ; obtain length + lddr ; copy literals + inc c + add a, a ; copy from last offset or new offset? + jr c, @dzx0sb_new_offset + call @dzx0sb_elias ; obtain length +@dzx0sb_copy: + ex (sp), hl ; preserve source, restore offset + push hl ; preserve offset + add hl, de ; calculate destination - offset + lddr ; copy from offset + inc c + pop hl ; restore offset + ex (sp), hl ; preserve offset, restore source + add a, a ; copy from literals or new offset? + jr nc, @dzx0sb_literals +@dzx0sb_new_offset: + inc sp ; discard last offset + inc sp + call @dzx0sb_elias ; obtain offset MSB + dec b + ret z ; check end marker + dec c ; adjust for positive offset + ld b, c + ld c, (hl) ; obtain offset LSB + dec hl + srl b ; last offset bit becomes first length bit + rr c + inc bc + push bc ; preserve new offset + ld bc, 1 ; obtain length + call c, @dzx0sb_elias_backtrack + inc bc + jr @dzx0sb_copy +@dzx0sb_elias_backtrack: + add a, a + rl c + rl b +@dzx0sb_elias: + add a, a ; inverted interlaced Elias gamma coding + jr nz, @dzx0sb_elias_skip + ld a, (hl) ; load another group of 8 bits + dec hl + rla +@dzx0sb_elias_skip: + jr c, @dzx0sb_elias_backtrack + ret +mend +; ----------------------------------------------------------------------------- + + |