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Overview

library(bitstreamio)

bitstreamio is a package for reading bits from a connection or raw vector.

This package has no requirement that reads/write operations be byte aligned.

Reading/writing bits and unaligned bytes is useful for input/output with packed binary file formats e.g. h264-compressed video, mp3 audio etc.

In addition to reading individual bits, this package also provides for:

What’s in the box

Read/Write with a raw vector

library(bitstreamio)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Write bits to a raw vector
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bs <- bs_open(raw(), "w")
bs_write_bit(bs, c(TRUE , FALSE, FALSE, FALSE))
bs_write_byte(bs, c(0x01, 0x7f))  # write unaligned byte values
bs_write_bit(bs, c(FALSE, FALSE, FALSE, TRUE))

raw_vec <- bs_close(bs)
raw_vec
#> [1] 80 17 f1


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Read bits back from raw vector
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bs <- bs_open(raw_vec, mode = 'r')
bs_read_bit(bs, 4)
#> [1]  TRUE FALSE FALSE FALSE
bs_read_byte(bs, 2) # unaligned byte read
#> [1] 01 7f
bs_read_bit(bs, 4)
#> [1] FALSE FALSE FALSE  TRUE
bs_close(bs)

Reading/Write with a connection

filename <- tempfile()

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Write bits to a file
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
con <- file(filename, "wb")
bs  <- bs_open(con, mode = 'w')

bs_write_bit(bs, c(TRUE , FALSE, FALSE, FALSE))
bs_write_byte(bs, c(1, 127))
bs_write_bit(bs, c(FALSE, FALSE, FALSE, TRUE))

bs_close(bs)
close(con)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Read the bits back in
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
con <- file(filename, "rb")
bs  <- bs_open(con, mode = 'r')

bs_read_bit(bs, 4)
#> [1]  TRUE FALSE FALSE FALSE
bs_read_uint(bs, nbits = 8, n = 2)
#> [1]   1 127
bs_read_bit(bs, 4)
#> [1] FALSE FALSE FALSE  TRUE

bs_close(bs)
close(con)

Read/write unsigned integers at varying bit depths

library(bitstreamio)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Write bits to a raw vector
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bs <- bs_open(raw(), "w")
bs_write_uint(bs,  0:7 , nbits = 3) # write 8 * 3-bit integers
bs_write_uint(bs, 10:15, nbits = 4) # write 6 * 4-bit integers
raw_vec <- bs_close(bs)
raw_vec
#> [1] 05 39 77 ab cd ef


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Read bits back from raw vector
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bs <- bs_open(raw_vec, mode = 'r')
bs_read_uint(bs, nbits = 3, n = 8)
#> [1] 0 1 2 3 4 5 6 7
bs_read_uint(bs, nbits = 4, n = 6)
#> [1] 10 11 12 13 14 15
bs_close(bs)

Read/write integers with Exponential-Golomb coding

Exponential-Golomb coding is a way of encoding integers to bit sequences. These bit sequences are often smaller than any standard integer type, and are often used to save space when packing data into a stream when the size of the integer is not known ahead of time.

# Converstion of unsigned integers to Exponential-Golomb coded bit sequences
uint_to_exp_golomb_bits(0)
#> [1] TRUE
uint_to_exp_golomb_bits(1)
#> [1] FALSE  TRUE FALSE
uint_to_exp_golomb_bits(2)
#> [1] FALSE  TRUE  TRUE
uint_to_exp_golomb_bits(3)
#> [1] FALSE FALSE  TRUE FALSE FALSE


# Converstion of signed integers to Exponential-Golomb coded bit sequences
sint_to_exp_golomb_bits(0)
#> [1] TRUE
sint_to_exp_golomb_bits(-1)
#> [1] FALSE  TRUE  TRUE
sint_to_exp_golomb_bits(-2)
#> [1] FALSE FALSE  TRUE FALSE  TRUE
sint_to_exp_golomb_bits(3)
#> [1] FALSE FALSE  TRUE  TRUE FALSE
library(bitstreamio)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Write bits to a raw vector
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bs <- bs_open(raw(), "w")
bs_write_uint_exp_golomb(bs,  0:9) 
raw_vec <- bs_close(bs)

# 10 integers encoded into 6 bytes
raw_vec
#> [1] a6 42 98 e2 04 8a


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Read bits back from raw vector
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bs <- bs_open(raw_vec, mode = 'r')
bs_read_uint_exp_golomb(bs, 10)
#>  [1] 0 1 2 3 4 5 6 7 8 9
bs_close(bs)

These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.