2008-04-14 04:09:29 +00:00
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/*
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* Functions to handle byte data as bit data, and particularly to read
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* Exp-Golomb encoded data.
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*
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* See H.264 clause 10.
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*
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* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is the MPEG TS, PS and ES tools.
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*
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* The Initial Developer of the Original Code is Amino Communications Ltd.
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* Portions created by the Initial Developer are Copyright (C) 2008
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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* Amino Communications Ltd, Swavesey, Cambridge UK
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*
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* ***** END LICENSE BLOCK *****
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#include <assert.h>
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#include "compat.h"
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#include "bitdata_fns.h"
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2009-05-03 16:40:57 +00:00
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#include "printing_fns.h"
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2008-04-14 04:09:29 +00:00
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static int MASK[] = { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
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/*
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* Build a new bitdata datastructure.
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*
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* - `data` is the byte array we're extracting bits from.
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* - `data_len` is its length (in bytes).
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*
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* Returns 0 if it succeeds, 1 if some error occurs.
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*/
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extern int build_bitdata(bitdata_p *bitdata,
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byte data[],
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int data_len)
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{
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bitdata_p new = malloc(SIZEOF_BITDATA);
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if (new == NULL)
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{
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2009-05-03 16:40:57 +00:00
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print_err("### Unable to allocate bitdata datastructure\n");
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2008-04-14 04:09:29 +00:00
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return 1;
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}
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new->data = data;
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new->data_len = data_len;
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new->cur_byte = 0;
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new->cur_bit = -1;
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*bitdata = new;
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return 0;
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}
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/*
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* Tidy up and free a bitdata datastructure after we've finished with it.
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*
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* Clears the bitdata datastructure, frees it, and sets `bitdata` to NULL.
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*
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* Does nothing if `bitdata` is already NULL.
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*/
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extern void free_bitdata(bitdata_p *bitdata)
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{
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if (*bitdata == NULL)
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return;
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(*bitdata)->data = NULL;
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(*bitdata)->cur_byte = 0;
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(*bitdata)->cur_bit = -1;
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free(*bitdata);
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*bitdata = NULL;
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}
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/*
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* Return the next bit from the data.
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*
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* Returns 0 or 1 if it reads the bit correctly, -1 if there are no more
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* bits to be read.
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*/
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static inline int next_bit(bitdata_p bitdata)
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{
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bitdata->cur_bit += 1;
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if (bitdata->cur_bit == 8)
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{
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bitdata->cur_bit = 0;
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bitdata->cur_byte += 1;
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if (bitdata->cur_byte > (bitdata->data_len - 1))
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{
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2009-05-03 16:40:57 +00:00
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print_err("### No more bits to read from input stream\n");
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2008-04-14 04:09:29 +00:00
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return -1;
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}
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}
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return (bitdata->data[bitdata->cur_byte] & MASK[bitdata->cur_bit])
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>> (7 - bitdata->cur_bit);
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}
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/*
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* Return the next bit from the data.
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*
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* Returns 0 if it reads the bit correctly, 1 if there are no more
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* bits to be read.
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*/
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extern int read_bit(bitdata_p bitdata,
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byte *bit)
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{
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int next = next_bit(bitdata);
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if (next < 0)
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return 1;
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else
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{
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*bit = next;
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return 0;
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}
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}
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/*
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* Reads `count` bits from the data.
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*
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* Note it is asserted that `count` must be in the range 0..32.
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*
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* Returns 0 if all went well, 1 if there were not enough bits in the data.
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*/
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extern int read_bits(bitdata_p bitdata,
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int count,
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2008-10-18 15:04:34 +00:00
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uint32_t *bits)
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2008-04-14 04:09:29 +00:00
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{
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int index = 0;
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2008-10-18 15:04:34 +00:00
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uint32_t result = 0;
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2008-04-14 04:09:29 +00:00
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assert((count >=0 && count <= 32));
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for (index=0; index<count; index++)
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{
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int bit = next_bit(bitdata);
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if (bit < 0)
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return 1;
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else
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result = (result << 1) | bit;
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}
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*bits = result;
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return 0;
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}
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/*
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* Reads `count` bits from the data, into a byte.
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*
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* Note it is asserted that `count` must be in the range 0..8.
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*
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* Returns 0 if all went well, 1 if there were not enough bits in the data.
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*/
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extern int read_bits_into_byte(bitdata_p bitdata,
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int count,
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byte *bits)
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{
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int index = 0;
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byte result = 0;
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assert((count >=0 && count <= 8));
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for (index=0; index<count; index++)
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{
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int bit = next_bit(bitdata);
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if (bit < 0)
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return 1;
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else
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result = (result << 1) | bit;
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}
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*bits = result;
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return 0;
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}
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/*
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* Read zero bits, counting them. Stop at the first non-zero bit.
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*
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* Returns the number of zero bits. Note that the non-zero bit is not
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* "unread" in any way, so reading another bit will retrieve the first bit
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* thereafter.
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*/
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extern int count_zero_bits(bitdata_p bitdata)
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{
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int count = 0;
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while (next_bit(bitdata) == 0)
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count ++;
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return count;
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}
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/*
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* Read and decode an Exp-Golomb code.
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*
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* Reference H.264 10.1 for an explanation.
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*
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* Returns 0 if all went well, 1 if there were not enough bits in the data.
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*/
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extern int read_exp_golomb(bitdata_p bitdata,
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2008-10-18 15:04:34 +00:00
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uint32_t *result)
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{
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2008-10-18 15:04:34 +00:00
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uint32_t next = 0;
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int leading_zero_bits = count_zero_bits(bitdata);
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int err = read_bits(bitdata,leading_zero_bits,&next);
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if (err)
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{
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2009-05-03 16:40:57 +00:00
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fprint_err("### Unable to read ExpGolomb value - not enough bits (%d)\n",
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leading_zero_bits);
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2008-04-14 04:09:29 +00:00
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return err;
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}
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*result = (int) (pow(2,leading_zero_bits) - 1 + next);
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return 0;
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}
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/*
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* Read and decode a signed Exp-Golomb code.
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*
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* Reference H.264 10.1 sqq for an explanation.
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*
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* Returns 0 if all went well, 1 if there were not enough bits in the data.
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*/
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extern int read_signed_exp_golomb(bitdata_p bitdata,
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2008-10-18 15:04:34 +00:00
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int32_t *result)
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2008-04-14 04:09:29 +00:00
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{
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2008-10-18 15:04:34 +00:00
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uint32_t val = 0;
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2008-04-14 04:09:29 +00:00
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int err = read_exp_golomb(bitdata,&val);
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if (err)
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{
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2009-05-03 16:40:57 +00:00
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print_err("### Unable to read signed ExpGolomb value\n");
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2008-04-14 04:09:29 +00:00
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return err;
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}
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*result = (int) (pow(-1,(val+1)) * ceil(val / 2.0));
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return 0;
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}
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2008-06-14 16:05:00 +00:00
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// Local Variables:
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// tab-width: 8
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// indent-tabs-mode: nil
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// c-basic-offset: 2
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// End:
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// vim: set tabstop=8 shiftwidth=2 expandtab:
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