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