mkinitrd-magellan/isolinux/rllpack.inc

; -*- fundamental -*-
; -----------------------------------------------------------------------
;   
;   Copyright 2004 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.
;
; -----------------------------------------------------------------------
; $Id: rllpack.inc,v 1.1 2007-09-01 22:44:05 niro Exp $

;
; rllpack.inc
;
; Very simple RLL compressor/decompressor, used to pack binary structures
; together.
;
; Format of leading byte
; 1-128		= x verbatim bytes follow
; 129-255 	= (x-126) times subsequent byte
; 0		= end of data
;

		section .text

;
; rllpack:
;	Pack CX bytes from DS:SI into ES:DI
;	Returns updated SI, DI and CX = number of bytes output
;
rllpack:
		push ax
		push bx
		push cx
		push bp
		push di
.startseq:
		xor ax,ax		; Zero byte
		xor bx,bx		; Run length zero
		mov bp,di		; Pointer to header byte
		stosb			; Store header byte (might be zero)
		jcxz .done_null
.stdbyte:
		lodsb
		stosb
		dec cx
		cmp ah,al
		je .same
.diff:
		mov ah,al
		xor bx,bx
.plainbyte:
		inc bx
		inc byte [es:bp]
		jcxz .done
		jns .stdbyte
		jmp .startseq
.same:
		cmp bl,2
		jb .plainbyte
		; 3 bytes or more in a row, time to convert sequence
		sub byte [es:bp],bl
		jnz .normal
		dec di			; We killed a whole stretch, remove start byte
.normal:
		inc bx	
		sub di,bx
		mov bp,di
		mov al,bl
		add al,126
		stosb
		mov al,ah
		stosb
.getrun:
		jcxz .done
		cmp bl,255-126
		jae .startseq
		lodsb
		cmp al,ah
		jne .nomatch
		inc bx
		inc byte [es:bp]
		dec cx
		jmp .getrun
.nomatch:
		dec si
		jmp .startseq
.done:
		xor al,al
		stosb
.done_null:
		pop dx
		sub dx,di
		neg dx
		pop bp
		pop cx
		pop bx
		pop ax
		ret
;
; rllunpack:
;	Unpack bytes from DS:SI into ES:DI
;	On return SI, DI are updated and CX contains number of bytes output
;	
rllunpack:
		push ax
		push di
		xor cx,cx
.header:
		lodsb
		and al,al
		jz .done
		cmp al,129
		jae .isrun
		; Not a run
		mov cl,al
		rep movsb
		jmp .header
.isrun:
		sub al,126
		mov cl,al
		lodsb
		rep stosb
		jmp .header
.done:
		pop cx
		sub cx,di
		neg cx
		pop ax
		ret
1	; -- fundamental --
2	; -----------------------------------------------------------------------
3	;
4	; Copyright 2004 H. Peter Anvin - All Rights Reserved
5	;
6	; This program is free software; you can redistribute it and/or modify
7	; it under the terms of the GNU General Public License as published by
8	; the Free Software Foundation, Inc., 53 Temple Place Ste 330,
9	; Boston MA 02111-1307, USA; either version 2 of the License, or
10	; (at your option) any later version; incorporated herein by reference.
11	;
12	; -----------------------------------------------------------------------
13	; $Id: rllpack.inc,v 1.1 2007-09-01 22:44:05 niro Exp $
14
15	;
16	; rllpack.inc
17	;
18	; Very simple RLL compressor/decompressor, used to pack binary structures
19	; together.
20	;
21	; Format of leading byte
22	; 1-128 = x verbatim bytes follow
23	; 129-255 = (x-126) times subsequent byte
24	; 0 = end of data
25	;
26
27	section .text
28
29	;
30	; rllpack:
31	; Pack CX bytes from DS:SI into ES:DI
32	; Returns updated SI, DI and CX = number of bytes output
33	;
34	rllpack:
35	push ax
36	push bx
37	push cx
38	push bp
39	push di
40	.startseq:
41	xor ax,ax ; Zero byte
42	xor bx,bx ; Run length zero
43	mov bp,di ; Pointer to header byte
44	stosb ; Store header byte (might be zero)
45	jcxz .done_null
46	.stdbyte:
47	lodsb
48	stosb
49	dec cx
50	cmp ah,al
51	je .same
52	.diff:
53	mov ah,al
54	xor bx,bx
55	.plainbyte:
56	inc bx
57	inc byte [es:bp]
58	jcxz .done
59	jns .stdbyte
60	jmp .startseq
61	.same:
62	cmp bl,2
63	jb .plainbyte
64	; 3 bytes or more in a row, time to convert sequence
65	sub byte [es:bp],bl
66	jnz .normal
67	dec di ; We killed a whole stretch, remove start byte
68	.normal:
69	inc bx
70	sub di,bx
71	mov bp,di
72	mov al,bl
73	add al,126
74	stosb
75	mov al,ah
76	stosb
77	.getrun:
78	jcxz .done
79	cmp bl,255-126
80	jae .startseq
81	lodsb
82	cmp al,ah
83	jne .nomatch
84	inc bx
85	inc byte [es:bp]
86	dec cx
87	jmp .getrun
88	.nomatch:
89	dec si
90	jmp .startseq
91	.done:
92	xor al,al
93	stosb
94	.done_null:
95	pop dx
96	sub dx,di
97	neg dx
98	pop bp
99	pop cx
100	pop bx
101	pop ax
102	ret
103	;
104	; rllunpack:
105	; Unpack bytes from DS:SI into ES:DI
106	; On return SI, DI are updated and CX contains number of bytes output
107	;
108	rllunpack:
109	push ax
110	push di
111	xor cx,cx
112	.header:
113	lodsb
114	and al,al
115	jz .done
116	cmp al,129
117	jae .isrun
118	; Not a run
119	mov cl,al
120	rep movsb
121	jmp .header
122	.isrun:
123	sub al,126
124	mov cl,al
125	lodsb
126	rep stosb
127	jmp .header
128	.done:
129	pop cx
130	sub cx,di
131	neg cx
132	pop ax
133	ret