Difference between revisions of "Z80 Routines:Other:IonCompress"

Revision as of 20:08, 6 April 2006

;Ion Compression Routines
;These routines are <supposed to> compress data in the format used by
;the IonDecompress routine.  I, Saibot84, have only reverse-engineered
;the compression algorithm based on the IonDecompress routine. 
;
;Just a note: The way I consider this, there is a routine that does 
;the work, and then there may be a routine that modifies slightly the 
;inputs and outputs of the first routine.  This modifying routine, I 
;call the MetaLibrary routine as an analogy to how physics is under 
;metaphysics. ;-)
;
;I know it's not good to post untested bits of code, but I just
;stumbled upon this on my computer and remembered I wanted to
;release it.
;
;IonCompress
;Inputs:
;  hl->where to read the data from
;  de->where to store the compressed output
;  b = number of bytes to copmpress
;  c = compression factor (see IonDecompress)
;Outputs:
;  hl->end of where to read
;  de->end of where to store
;  carry flag: set->error  res->all is well
;
;MetaLib_IonCompress
;Inputs:
;  hl->where to read the data from
;  de->where to store the compressed output
;  bc = number of bytes to copmpress
;  a = compression factor (see IonDecompress)
;Outputs:
;  hl->end of where to read
;  de->end of where to store
;  bc = new length
;  carry flag: set->error  res->all is well

IonCompress:
   ;016-7-2005
   ;=>hl->read
   ;=>de->sto
   ;=>b=len
   ;=>c=comp factor
   ;<=hl->read+len
   ;<=de->sto+len(new)
   ;<=cf=error
   ld a,c
   cp 2
   jr nc, IC_Next1
   srl b
IC_Next1:
   cp 4
   jr nc,IC_Next2
   srl b
IC_Next2:
   srl b
   push ix
IC_Loop:
   push bc
   ld ixh,0
   ld ixl,8
   ld a,c
   ld b,8
   cp 1
   jr z,IC_cmp1
   ld b,4
   cp 3
   jr z,IC_cmp1
   ld b,2
IC_cmp1:
   push bc
   ld a,c
   ld b,1
   cp 1
   jr z,IC_cmp2
   inc b
   cp 3
   jr z,IC_cmp2
   ld b,4
IC_cmp2:
   ld a,ixl
   sub b
   ld b,a
   ld ixl,a
   ld a,c
   cp (hl)
   jr c,IC_Error
   ld a,(hl)
IC_cmp3:
   sla a
   djnz IC_cmp3
   or ixh
   inc hl
   pop bc
   djnz IC_cmp1
   inc de
   pop bc
   djnz IC_Loop
IC_Exit:
   pop ix
   ret
IC_Error:
   pop bc
   pop bc
   jr IC_Exit

MetaLib_IonCompress:
   ;016-7-2005
   ;=>hl->read
   ;=>de->sto
   ;=>bc=len
   ;=>a=comp factor
   ;<=hl->read+len
   ;<=de->sto+len(new)
   ;<=bc=new length
   ;<=cf=error
   push de
   push af
   push bc
   ld b,a
   ld a,c
   or a
   ld a,b
   pop bc
   jr z,ML_IC_Loop
   inc b
ML_IC_Loop:
   push bc
   push af
   ld b,c
   ld c,a
   call IonCompress
   ret c
   pop af
   pop bc
   ld c,0
   djnz ML_IC_Loop
   pop af
   ex (sp),hl
   ex de,hl
   push hl
   or a
   sbc hl,de
   pop de
   push hl
   pop bc
   pop hl
   ret

Special Thanks

Joe Wingbermuhele for creating Ion for the 83/83+

XDG Kat-Productions's Justin Haygood and Benny Baumann for encouraging my coding abilities in both z80 Asm and TI-BASIC.