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/*
* Copyright (C) 2000, 2001, 2002, 2003 Håkan Hjort <d95hjort@dtek.chalmers.se>
*
* This file is part of libdvdread.
*
* libdvdread 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; either version 2 of the License, or
* (at your option) any later version.
*
* libdvdread 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with libdvdread; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "config.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <inttypes.h>
#include <assert.h>
#include "dvdread/bitreader.h"
int dvdread_getbits_init(getbits_state_t *state, const uint8_t *start) {
if ((state == NULL) || (start == NULL)) return 0;
state->start = start;
state->bit_position = 0;
state->byte_position = 0;
return 1;
}
/* Non-optimized getbits. */
/* This can easily be optimized for particular platforms. */
uint32_t dvdread_getbits(getbits_state_t *state, uint32_t number_of_bits) {
uint32_t result=0;
uint8_t byte=0;
if (number_of_bits > 32) {
printf("Number of bits > 32 in getbits\n");
abort();
}
if ((state->bit_position) > 0) { /* Last getbits left us in the middle of a byte. */
if (number_of_bits > (8-state->bit_position)) { /* this getbits will span 2 or more bytes. */
byte = state->start[state->byte_position] << state->bit_position;
byte = byte >> (state->bit_position);
result = byte;
number_of_bits -= (8-state->bit_position);
state->bit_position = 0;
state->byte_position++;
} else {
byte = state->start[state->byte_position] << state->bit_position;
byte = byte >> (8 - number_of_bits);
result = byte;
state->bit_position += number_of_bits; /* Here it is impossible for bit_position > 8 */
if (state->bit_position == 8) {
state->bit_position = 0;
state->byte_position++;
}
number_of_bits = 0;
}
}
if ((state->bit_position) == 0) {
while (number_of_bits > 7) {
result = (result << 8) + state->start[state->byte_position];
state->byte_position++;
number_of_bits -= 8;
}
if (number_of_bits > 0) { /* number_of_bits < 8 */
byte = state->start[state->byte_position] << state->bit_position;
state->bit_position += number_of_bits; /* Here it is impossible for bit_position > 7 */
byte = byte >> (8 - number_of_bits);
result = (result << number_of_bits) + byte;
number_of_bits = 0;
}
}
return result;
}
#if 0 /* TODO: optimized versions not yet used */
/* WARNING: This function can only be used on a byte boundary.
No checks are made that we are in fact on a byte boundary.
*/
uint16_t dvdread_get16bits(getbits_state_t *state) {
uint16_t result;
state->byte_position++;
result = (state->byte << 8) + state->start[state->byte_position++];
state->byte = state->start[state->byte_position];
return result;
}
/* WARNING: This function can only be used on a byte boundary.
No checks are made that we are in fact on a byte boundary.
*/
uint32_t dvdread_get32bits(getbits_state_t *state) {
uint32_t result;
state->byte_position++;
result = (state->byte << 8) + state->start[state->byte_position++];
result = (result << 8) + state->start[state->byte_position++];
result = (result << 8) + state->start[state->byte_position++];
state->byte = state->start[state->byte_position];
return result;
}
#endif
#ifdef BITREADER_TESTS
int main()
{
uint8_t buff[2] = {
0x6E, 0xC2
// 0b 01101110 11000010
};
getbits_state_t state;
dvdread_getbits_init(&state, buff);
uint32_t bits = dvdread_getbits(&state, 3);
assert(bits == 3);
bits = dvdread_getbits(&state, 3);
assert(bits == 3);
bits = dvdread_getbits(&state, 4);
assert(bits == 11);
bits = dvdread_getbits(&state, 6);
assert(bits == 2);
dvdread_getbits_init(&state, buff);
bits = dvdread_getbits(&state, 10);
assert(bits == 443);
bits = dvdread_getbits(&state, 6);
assert(bits == 2);
dvdread_getbits_init(&state, buff);
bits = dvdread_getbits(&state, 16);
assert(bits == 28354);
buff[0] = buff[1] = 0xFF;
dvdread_getbits_init(&state, buff);
bits = dvdread_getbits(&state, 16);
assert(bits == 0xFFFF);
uint8_t large[5] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
dvdread_getbits_init(&state, large);
bits = dvdread_getbits(&state, 8);
assert(bits == 0xFF);
bits = dvdread_getbits(&state, 32);
assert(bits == 0xFFFFFFFF);
return 0;
}
#endif
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