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Diffstat (limited to 'libdvdread-embedded/src/bitreader.c')
| -rw-r--r-- | libdvdread-embedded/src/bitreader.c | 163 |
1 files changed, 163 insertions, 0 deletions
diff --git a/libdvdread-embedded/src/bitreader.c b/libdvdread-embedded/src/bitreader.c new file mode 100644 index 0000000..f6a2183 --- /dev/null +++ b/libdvdread-embedded/src/bitreader.c @@ -0,0 +1,163 @@ +/* + * 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 |