soft, unpacked and packed bits

Osmocom bit level support code. More...

Files
file	bits.h
	Osmocom bit level support code.
file	bits.c

Macros
#define	OSMO_BIN_SPEC   "%d%d%d%d%d%d%d%d"
#define	OSMO_BIN_PRINT(byte)
#define	OSMO_BIT_SPEC   "%c%c%c%c%c%c%c%c"
#define	OSMO_BIT_PRINT_EX(byte, ch)
#define	OSMO_BIT_PRINT(byte)   OSMO_BIT_PRINT_EX(byte, '1')

Typedefs
typedef int8_t	sbit_t
	soft bit with value (-127...127), as commonly used in communications receivers such as [viterbi] decoders More...
typedef uint8_t	ubit_t
	unpacked bit (0 or 1): 1 bit per byte More...
typedef uint8_t	pbit_t
	packed bits (8 bits in a byte). More...

Enumerations
enum	osmo_br_mode {   OSMO_BR_BITS_IN_DWORD = 31 ,   OSMO_BR_BYTES_IN_DWORD = 24 ,   OSMO_BR_BITS_IN_BYTE = 7 ,   OSMO_BR_WORD_SWAP = 16 }
	bit-reversal mode for osmo_bit_reversal() More...

Functions
static unsigned int	osmo_pbit_bytesize (unsigned int num_bits)
	determine how many bytes we would need for num_bits packed bits More...
int	osmo_ubit2pbit (pbit_t *out, const ubit_t *in, unsigned int num_bits)
	convert unpacked bits to packed bits, return length in bytes More...
int	osmo_pbit2ubit (ubit_t *out, const pbit_t *in, unsigned int num_bits)
	convert packed bits to unpacked bits, return length in bytes More...
void	osmo_nibble_shift_right (uint8_t *out, const uint8_t *in, unsigned int num_nibbles)
	Shift unaligned input to octet-aligned output. More...
void	osmo_nibble_shift_left_unal (uint8_t *out, const uint8_t *in, unsigned int num_nibbles)
	Shift unaligned input to octet-aligned output. More...
void	osmo_ubit2sbit (sbit_t *out, const ubit_t *in, unsigned int num_bits)
	convert unpacked bits to soft bits More...
void	osmo_sbit2ubit (ubit_t *out, const sbit_t *in, unsigned int num_bits)
	convert soft bits to unpacked bits More...
int	osmo_ubit2pbit_ext (pbit_t *out, unsigned int out_ofs, const ubit_t *in, unsigned int in_ofs, unsigned int num_bits, int lsb_mode)
	convert unpacked bits to packed bits (extended options) More...
int	osmo_pbit2ubit_ext (ubit_t *out, unsigned int out_ofs, const pbit_t *in, unsigned int in_ofs, unsigned int num_bits, int lsb_mode)
	convert packed bits to unpacked bits (extended options) More...
uint32_t	osmo_bit_reversal (uint32_t x, enum osmo_br_mode k)
	generalized bit reversal function More...
uint32_t	osmo_revbytebits_32 (uint32_t x)
	reverse the bit-order in each byte of a dword More...
uint32_t	osmo_revbytebits_8 (uint8_t x)
	reverse the bit order in a byte More...
void	osmo_revbytebits_buf (uint8_t *buf, int len)
	reverse bit-order of each byte in a buffer More...
static uint16_t	osmo_rol16 (uint16_t in, unsigned shift)
	left circular shift More...

Variables
static const uint8_t	flip_table [256]

Detailed Description

Osmocom bit level support code.

This module implements the notion of different bit-fields, such as

• unpacked bits (ubit_t), i.e. 1 bit per byte
• packed bits (pbit_t), i.e. 8 bits per byte
• soft bits (sbit_t), 1 bit per byte from -127 to 127

Macro Definition Documentation

OSMO_BIN_PRINT

#define OSMO_BIN_PRINT

(

byte

)

Value:

  (byte & 0x80 ? 1 : 0), \
  (byte & 0x40 ? 1 : 0), \
  (byte & 0x20 ? 1 : 0), \
  (byte & 0x10 ? 1 : 0), \
  (byte & 0x08 ? 1 : 0), \
  (byte & 0x04 ? 1 : 0), \
  (byte & 0x02 ? 1 : 0), \
  (byte & 0x01 ? 1 : 0)

OSMO_BIN_SPEC

#define OSMO_BIN_SPEC   "%d%d%d%d%d%d%d%d"

OSMO_BIT_PRINT

#define OSMO_BIT_PRINT

(

byte

)

OSMO_BIT_PRINT_EX(byte, '1')

OSMO_BIT_PRINT_EX

#define OSMO_BIT_PRINT_EX	(		byte,
			ch
	)

Value:

  (byte & 0x80 ? ch : '.'), \
  (byte & 0x40 ? ch : '.'), \
  (byte & 0x20 ? ch : '.'), \
  (byte & 0x10 ? ch : '.'), \
  (byte & 0x08 ? ch : '.'), \
  (byte & 0x04 ? ch : '.'), \
  (byte & 0x02 ? ch : '.'), \
  (byte & 0x01 ? ch : '.')

OSMO_BIT_SPEC

#define OSMO_BIT_SPEC   "%c%c%c%c%c%c%c%c"

Typedef Documentation

pbit_t

typedef uint8_t pbit_t

packed bits (8 bits in a byte).

NOTE on the endian-ness of pbit_t:

• Bits in a pbit_t are ordered MSB first, i.e. 0x80 is the first bit.
• Bit i in a pbit_t array is array[i/8] & (1<<(7-i%8))

sbit_t

typedef int8_t sbit_t

soft bit with value (-127...127), as commonly used in communications receivers such as [viterbi] decoders

ubit_t

typedef uint8_t ubit_t

unpacked bit (0 or 1): 1 bit per byte

Enumeration Type Documentation

osmo_br_mode

enum osmo_br_mode

bit-reversal mode for osmo_bit_reversal()

Enumerator
OSMO_BR_BITS_IN_DWORD	reverse all bits in a 32bit dword
OSMO_BR_BYTES_IN_DWORD	reverse byte order in a 32bit dword
OSMO_BR_BITS_IN_BYTE	reverse bits of each byte in a 32bit dword
OSMO_BR_WORD_SWAP	swap the two 16bit words in a 32bit dword

Function Documentation

osmo_bit_reversal()

uint32_t osmo_bit_reversal	(	uint32_t	x,
		enum osmo_br_mode	k
	)

generalized bit reversal function

Parameters

[in]	x	the 32bit value to be reversed
[in]	k	the type of reversal requested

Returns

the reversed 32bit dword

This function reverses the bit order within a 32bit word. Depending on "k", it either reverses all bits in a 32bit dword, or the bytes in the dword, or the bits in each byte of a dword, or simply swaps the two 16bit words in a dword. See Chapter 7 "Hackers Delight"

References k, and x.

osmo_nibble_shift_left_unal()

void osmo_nibble_shift_left_unal	(	uint8_t *	out,
		const uint8_t *	in,
		unsigned int	num_nibbles
	)

Shift unaligned input to octet-aligned output.

Parameters

[out]	out	output buffer, octet-aligned
[in]	in	input buffer, unaligned
[in]	num_nibbles	number of nibbles

osmo_nibble_shift_right()

void osmo_nibble_shift_right	(	uint8_t *	out,
		const uint8_t *	in,
		unsigned int	num_nibbles
	)

Shift unaligned input to octet-aligned output.

Parameters

[out]	out	output buffer, unaligned
[in]	in	input buffer, octet-aligned
[in]	num_nibbles	number of nibbles

osmo_pbit2ubit()

int osmo_pbit2ubit	(	ubit_t *	out,
		const pbit_t *	in,
		unsigned int	num_bits
	)

convert packed bits to unpacked bits, return length in bytes

Parameters

[out]	out	output buffer of unpacked bits
[in]	in	input buffer of packed bits
[in]	num_bits	number of bits

Returns

number of bytes used in out

osmo_pbit2ubit_ext()

int osmo_pbit2ubit_ext	(	ubit_t *	out,
		unsigned int	out_ofs,
		const pbit_t *	in,
		unsigned int	in_ofs,
		unsigned int	num_bits,
		int	lsb_mode
	)

convert packed bits to unpacked bits (extended options)

Parameters

[out]	out	output buffer of unpacked bits
[in]	out_ofs	offset into output buffer
[in]	in	input buffer of packed bits
[in]	in_ofs	offset into input buffer
[in]	num_bits	number of bits
[in]	lsb_mode	Encode bits in LSB order instead of MSB

Returns

length in bytes (max written offset of output buffer + 1)

osmo_pbit_bytesize()

static unsigned int osmo_pbit_bytesize ( unsigned int  num_bits )

inlinestatic

determine how many bytes we would need for num_bits packed bits

Parameters

[in]

num_bits

Number of packed bits

Returns

number of bytes needed for num_bits packed bits

osmo_revbytebits_32()

uint32_t osmo_revbytebits_32

(

uint32_t

x

)

reverse the bit-order in each byte of a dword

Parameters

[in]

x

32bit input value

Returns

32bit value where bits of each byte have been reversed

See Chapter 7 "Hackers Delight"

References x.

osmo_revbytebits_8()

uint32_t osmo_revbytebits_8

(

uint8_t

x

)

reverse the bit order in a byte

Parameters

[in]

x

8bit input value

Returns

8bit value where bits order has been reversed

References flip_table, and x.

Referenced by osmo_isdnhdlc_decode(), and osmo_isdnhdlc_encode().

osmo_revbytebits_buf()

void osmo_revbytebits_buf	(	uint8_t *	buf,
		int	len
	)

reverse bit-order of each byte in a buffer

Parameters

[in]	buf	buffer containing bytes to be bit-reversed
[in]	len	length of buffer in bytes

This function reverses the bits in each byte of the buffer

References flip_table, and len().

osmo_rol16()

static uint16_t osmo_rol16 ( uint16_t  in, unsigned  shift  )

inlinestatic

left circular shift

Parameters

[in]	in	The 16 bit unsigned integer to be rotated
[in]	shift	Number of bits to shift in to, [0;16] bits

Returns

shifted value

osmo_sbit2ubit()

void osmo_sbit2ubit	(	ubit_t *	out,
		const sbit_t *	in,
		unsigned int	num_bits
	)

convert soft bits to unpacked bits

Parameters

[out]	out	output buffer of unpacked bits
[in]	in	input buffer of soft bits
[in]	num_bits	number of bits

osmo_ubit2pbit()

int osmo_ubit2pbit	(	pbit_t *	out,
		const ubit_t *	in,
		unsigned int	num_bits
	)

convert unpacked bits to packed bits, return length in bytes

Parameters

[out]	out	output buffer of packed bits
[in]	in	input buffer of unpacked bits
[in]	num_bits	number of bits

osmo_ubit2pbit_ext()

int osmo_ubit2pbit_ext	(	pbit_t *	out,
		unsigned int	out_ofs,
		const ubit_t *	in,
		unsigned int	in_ofs,
		unsigned int	num_bits,
		int	lsb_mode
	)

convert unpacked bits to packed bits (extended options)

Parameters

[out]	out	output buffer of packed bits
[in]	out_ofs	offset into output buffer
[in]	in	input buffer of unpacked bits
[in]	in_ofs	offset into input buffer
[in]	num_bits	number of bits
[in]	lsb_mode	Encode bits in LSB order instead of MSB

Returns

length in bytes (max written offset of output buffer + 1)

osmo_ubit2sbit()

void osmo_ubit2sbit	(	sbit_t *	out,
		const ubit_t *	in,
		unsigned int	num_bits
	)

convert unpacked bits to soft bits

Parameters

[out]	out	output buffer of soft bits
[in]	in	input buffer of unpacked bits
[in]	num_bits	number of bits

Variable Documentation

flip_table

const uint8_t flip_table[256]

static

Initial value:

= {
        0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0, 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
        0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8, 0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
        0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4, 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
        0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec, 0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
        0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2, 0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
        0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea, 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
        0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6, 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
        0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee, 0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
        0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1, 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
        0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9, 0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
        0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5, 0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
        0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed, 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
        0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3, 0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
        0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb, 0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
        0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7, 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
        0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef, 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff,
}

Referenced by osmo_revbytebits_8(), and osmo_revbytebits_buf().