bit.c File Reference

Manipulation methods for the mad_bitptr structure, used in various low-level routines. More...

#include "global.h"
#include "bit.h"

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Defines
#define	CHAR_BIT   8
#define	CRC_POLY   0x8005
Functions
void	mad_bit_init (struct mad_bitptr *bitptr, unsigned char const *byte)
	Initializes bit pointer struct.
unsigned int	mad_bit_length (struct mad_bitptr const *begin, struct mad_bitptr const *end)
	Returns number of bits between start and end points.
unsigned char const *	mad_bit_nextbyte (struct mad_bitptr const *bitptr)
	Returns pointer to next unprocessed byte.
void	mad_bit_skip (struct mad_bitptr *bitptr, unsigned int len)
	Advances bit pointer.
unsigned long	mad_bit_read (struct mad_bitptr *bitptr, unsigned int len)
	Reads an arbitrary number of bits and return their UIMSBF value.
unsigned short	mad_bit_crc (struct mad_bitptr bitptr, unsigned int len, unsigned short init)
	Computes CRC-check word.
Variables
static unsigned short const	crc_table [256]
	This is the lookup table for computing the CRC-check word.

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Detailed Description

Manipulation methods for the mad_bitptr structure, used in various low-level routines.

Definition in file bit.c.

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Define Documentation

#define CHAR_BIT   8

Definition at line 35 of file bit.c.

Referenced by III_huffdecode(), III_requantize(), mad_bit_init(), mad_bit_length(), mad_bit_nextbyte(), mad_bit_read(), mad_bit_skip(), and mad_layer_III().

#define CRC_POLY   0x8005

Definition at line 86 of file bit.c.

Referenced by mad_bit_crc().

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Function Documentation

unsigned short mad_bit_crc	(	struct mad_bitptr	bitptr,
		unsigned int	len,
		unsigned short	init
	)

Computes CRC-check word.

Definition at line 194 of file bit.c.

References CRC_POLY, crc_table, and mad_bit_read().

Referenced by decode_header(), mad_layer_I(), mad_layer_II(), and mad_layer_III().

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void mad_bit_init	(	struct mad_bitptr *	bitptr,
		unsigned char const *	byte
	)

Initializes bit pointer struct.

Definition at line 91 of file bit.c.

References mad_bitptr::byte, mad_bitptr::cache, CHAR_BIT, and mad_bitptr::left.

Referenced by mad_frame_decode(), mad_header_decode(), mad_layer_III(), mad_stream_buffer(), mad_stream_init(), and mad_stream_sync().

unsigned int mad_bit_length	(	struct mad_bitptr const *	begin,
		struct mad_bitptr const *	end
	)

Returns number of bits between start and end points.

Definition at line 101 of file bit.c.

References mad_bitptr::byte, CHAR_BIT, and mad_bitptr::left.

Referenced by III_scalefactors(), III_scalefactors_lsf(), mad_frame_decode(), and mad_layer_II().

unsigned char const* mad_bit_nextbyte

(

struct mad_bitptr const *

bitptr

)

Returns pointer to next unprocessed byte.

Definition at line 111 of file bit.c.

References mad_bitptr::byte, CHAR_BIT, and mad_bitptr::left.

Referenced by free_bitrate(), mad_header_decode(), mad_layer_III(), and mad_stream_sync().

unsigned long mad_bit_read	(	struct mad_bitptr *	bitptr,
		unsigned int	len
	)

Reads an arbitrary number of bits and return their UIMSBF value.

Definition at line 136 of file bit.c.

References mad_bitptr::byte, mad_bitptr::cache, CHAR_BIT, and mad_bitptr::left.

Referenced by decode_header(), I_sample(), II_samples(), III_huffdecode(), III_scalefactors(), III_scalefactors_lsf(), III_sideinfo(), mad_bit_crc(), mad_layer_I(), mad_layer_II(), and mad_layer_III().

void mad_bit_skip	(	struct mad_bitptr *	bitptr,
		unsigned int	len
	)

Advances bit pointer.

Definition at line 119 of file bit.c.

References mad_bitptr::byte, mad_bitptr::cache, CHAR_BIT, and mad_bitptr::left.

Referenced by decode_header(), free_bitrate(), III_huffdecode(), and mad_layer_III().

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Variable Documentation

unsigned short const crc_table[256] [static]

This is the lookup table for computing the CRC-check word.

As described in section 2.4.3.1 and depicted in Figure A.9 of ISO/IEC 11172-3, the generator polynomial is:

G(X) = X^16 + X^15 + X^2 + 1

Definition at line 48 of file bit.c.

Referenced by mad_bit_crc().