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/*
* MR97310A decoder
*
* Copyright (C) 2004 Theodore Kilgore <kilgota@auburn.edu>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
#include "libv4lconvert-priv.h"
#define CLIP(x) ((x)<0?0:((x)>0xff)?0xff:(x))
/* FIXME not threadsafe */
static int decoder_initialized = 0;
static struct {
unsigned char is_abs;
unsigned char len;
signed char val;
} table[256];
static void init_mr97310a_decoder(void)
{
int i;
int is_abs, val, len;
for (i = 0; i < 256; ++i) {
is_abs = 0;
val = 0;
len = 0;
if ((i & 0x80) == 0) {
/* code 0 */
val = 0;
len = 1;
} else if ((i & 0xe0) == 0xc0) {
/* code 110 */
val = -3;
len = 3;
} else if ((i & 0xe0) == 0xa0) {
/* code 101 */
val = +3;
len = 3;
} else if ((i & 0xf0) == 0x80) {
/* code 1000 */
val = +7;
len = 4;
} else if ((i & 0xf0) == 0x90) {
/* code 1001 */
val = -7;
len = 4;
} else if ((i & 0xf0) == 0xf0) {
/* code 1111 */
val = -15;
len = 4;
} else if ((i & 0xf8) == 0xe0) {
/* code 11100 */
val = +15;
len = 5;
} else if ((i & 0xf8) == 0xe8) {
/* code 11101xxxxx */
is_abs = 1;
val = 0; /* value is calculated later */
len = 5;
}
table[i].is_abs = is_abs;
table[i].val = val;
table[i].len = len;
}
decoder_initialized = 1;
}
static inline unsigned char get_byte(const unsigned char *inp,
unsigned int bitpos)
{
const unsigned char *addr;
addr = inp + (bitpos >> 3);
return (addr[0] << (bitpos & 7)) | (addr[1] >> (8 - (bitpos & 7)));
}
void v4lconvert_decode_mr97310a(const unsigned char *inp, unsigned char *outp,
int width, int height)
{
int row, col;
int val;
int bitpos;
unsigned char code;
unsigned char lp, tp, tlp, trp;
if (!decoder_initialized)
init_mr97310a_decoder();
/* remove the header */
inp += 12;
bitpos = 0;
/* main decoding loop */
for (row = 0; row < height; ++row) {
col = 0;
/* first two pixels in first two rows are stored as raw 8-bit */
if (row < 2) {
code = get_byte(inp, bitpos);
bitpos += 8;
*outp++ = code;
code = get_byte(inp, bitpos);
bitpos += 8;
*outp++ = code;
col += 2;
}
while (col < width) {
/* get bitcode */
code = get_byte(inp, bitpos);
/* update bit position */
bitpos += table[code].len;
/* calculate pixel value */
if (table[code].is_abs) {
/* get 5 more bits and use them as absolute value */
code = get_byte(inp, bitpos);
val = (code & 0xf8);
bitpos += 5;
} else {
/* value is relative to top or left pixel */
val = table[code].val;
lp = outp[-2];
if (row > 1) {
tlp = outp[-2*width-2];
tp = outp[-2*width];
trp = outp[-2*width+2];
}
if (row < 2) {
/* top row: relative to left pixel */
val += lp;
} else if (col < 2) {
/* left column: relative to top pixel */
/* initial estimate */
val += (2*tp + 2*trp + 1)/4;
} else if (col > width - 3) {
/* left column: relative to top pixel */
val += (2*tp + 2*tlp + 1)/4;
/* main area: average of left and top pixel */
} else {
/* initial estimate for predictor */
val += (2*lp + tp + trp + 1)/4;
}
}
/* store pixel */
*outp++ = CLIP(val);
++col;
}
}
return;
}
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