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rllpack.inc
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/
rllpack.inc
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; -*- fundamental -*- ---------------------------------------------------
;
; Copyright 2004-2008 H. Peter Anvin - All Rights Reserved
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation, Inc., 53 Temple Place Ste 330,
; Boston MA 02111-1307, USA; either version 2 of the License, or
; (at your option) any later version; incorporated herein by reference.
;
; -----------------------------------------------------------------------
;
; rllpack.inc
;
; Very simple RLL compressor/decompressor, used to pack binary structures
; together.
;
; Format of leading byte
; 1-128 = x verbatim bytes follow
; 129-223 = (x-126) times subsequent byte
; 224-255 = (x-224)*256+(next byte) times the following byte
; 0 = end of data
;
; These structures are stored *in reverse order* in high memory.
; High memory pointers point to one byte beyond the end.
;
section .text
;
; rllpack:
; Pack CX bytes from SI into EDI.
; Returns updated SI and EDI.
;
rllpack:
push word .pmentry
call simple_pm_call
ret
.pmentry:
push cx
push ebx
push edx
.startseq:
xor ax,ax ; Zero byte
xor ebx,ebx ; Run length zero
dec edi
mov edx,edi ; Pointer to header byte
mov [edi],al ; Create header byte
jcxz .done ; If done, this was the terminator
.stdbyte:
lodsb
dec edi
mov [edi],al
dec cx
cmp ah,al
je .same
.diff:
mov ah,al
xor bx,bx
.plainbyte:
inc bx
inc byte [edx]
jcxz .startseq
jns .stdbyte
jmp .startseq
.same:
cmp bl,2
jb .plainbyte
; 3 bytes or more in a row, time to convert sequence
sub [edx],bl
jnz .normal
inc edi ; We killed a whole stretch,
; drop start byte
.normal:
inc bx
add edi,ebx ; Remove the stored run bytes
.getrun:
jcxz .nomatch
lodsb
cmp al,ah
jne .nomatch
cmp bx,(256-224)*256-1 ; Maximum run size
jae .nomatch
inc bx
dec cx
jmp .getrun
.nomatch:
cmp bx,224-126
jae .twobyte
.onebyte:
add bl,126
dec edi
mov [edi],bl
jmp .storebyte
.twobyte:
add bh,224
sub edi,2
mov [edi],bx
.storebyte:
dec edi
mov [edi],ah
dec si ; Reload subsequent byte
jmp .startseq
.done:
pop edx
pop ebx
pop cx
ret
;
; rllunpack:
; Unpack bytes from ESI into DI
; On return ESI, DI are updated and CX contains number of bytes output.
;
rllunpack:
push word .pmentry
call simple_pm_call
ret
.pmentry:
push di
xor cx,cx
.header:
dec esi
mov cl,[esi]
jcxz .done
cmp cl,129
jae .isrun
; Not a run
.copy:
dec esi
mov al,[esi]
stosb
loop .copy
jmp .header
.isrun:
cmp cl,224
jae .longrun
sub cl,126
.dorun:
dec esi
mov al,[esi]
rep stosb
jmp .header
.longrun:
sub cl,224
mov ch,cl
dec esi
mov cl,[esi]
jmp .dorun
.done:
pop cx
sub cx,di
neg cx
ret