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shell-bitwise: Add functions to operate with bits
This is a set of functions for manipulating individual bits in a number. In most cases, shell implementations work similarly if the number is small. However, if the value approaches the maximum int32 or int64, differences in behavior arise depending on the implementation. Signed-off-by: Alexey Gladkov <legion@kernel.org>
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‎mans/shell-bitwise.scd‎

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shell-bitwise(3)
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# NAME
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is_bit_set, clear_bit, clear_bits, get_bit, set_bit, set_bit_value,
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set_bits, toggle_bit, toggle_bits - functions for obtaining, setting, and
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clearing individual bits in a number.
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# SYNOPSIS
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- is_bit_set number bit_pos
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- get_bit result_var number bit_pos
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- set_bit_value result_var number bit value
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- set_bit result_var number bit
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- clear_bit result_var number bit
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- toggle_bit result_var number bit
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# DESCRIPTION
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## is_bit_set
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Checks whether the bit at position bit_pos is set.
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Arguments:
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- number - integer value to extract the bit from
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- bit_pos - bit position (0 = least significant bit)
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Result:
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The return 0 (true) if bit is set, 1 (false) if not.
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## get_bit
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Extract the value of the specified bit from a number.
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Arguments:
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- result_var - name of the variable to store the result
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- number - integer value to extract the bit from
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- bit_pos - bit position (0 = least significant bit)
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Result:
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The value of the specified bit (0 or 1) is stored in result_var.
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## set_bit_value
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Sets the specified bit in a number to a given value (0 or 1).
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Arguments:
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- result_var - name of the variable to store the result
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- number - integer value to modify
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- bit - bit position (0 = least significant bit)
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- value - desired bit value (0 or 1)
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Result:
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The modified number with the updated bit is stored in result_var.
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## set_bit
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Sets the specified bit to 1.
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Arguments:
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- result_var - name of the variable to store the result
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- number - integer value to modify
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- bit - bit position (0 = least significant bit)
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Result:
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The modified number with the bit set to 1 is stored in result_var.
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## clear_bit
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Clears (sets to 0) the specified bit.
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Arguments:
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- result_var - name of the variable to store the result
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- number - integer value to modify
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- bit - bit position (0 = least significant bit)
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Result:
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The modified number with the bit cleared is stored in result_var.
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## toggle_bit
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Toggles (inverts) the specified bit.
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Arguments:
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- result_var - name of the variable to store the result
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- number - integer value to modify
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- bit - bit position (0 = least significant bit)
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Result:
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The modified number with the bit inverted is stored in result_var.
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## set_bits
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Sets multiple bits to 1 in a number.
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Arguments:
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- result_var - name of the variable to store the result
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- number - integer value to modify
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- bit1...N - list of bit positions to set
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Result:
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The modified number with all specified bits set to 1 is stored in result_var.
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## clear_bits
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Clears (sets to 0) multiple bits in a number.
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Arguments:
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- result_var - name of the variable to store the result
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- number - integer value to modify
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- bit1...N - list of bit positions to clear
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Result:
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The modified number with all specified bits cleared is stored in result_var.
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## toggle_bits
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Toggles (inverts) multiple bits in a number.
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Arguments:
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- result_var - name of the variable to store the result
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- number - integer value to modify
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- bit1...N - list of bit positions to toggle
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Result:
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The modified number with all specified bits inverted is stored in result_var.
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# AUTHOR
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Authors and contributors of the programs included in the *libshell* package are listed
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in the COPYING file.
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# BUGS
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Report bugs to the authors.
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‎shell-bitwise‎

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#!/bin/sh -efu
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### This file is covered by the GNU General Public License,
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### which should be included with libshell as the file LICENSE.
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### All copyright information are listed in the COPYING.
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if [ -z "${__included_shell_bits-}" ]; then
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__included_shell_bits=1
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__shell_prepare_integer()
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{
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case "$2" in
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9223372036854775808|-9223372036854775808|0[xX]8000000000000000|-0[xX]8000000000000000)
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set -- "$1" "(0x7fffffffffffffff + 1)"
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;;
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0[xX][0-9A-Fa-f]*|[1-9]*|-[1-9]*)
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;;
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-0[xX]*)
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return 1
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;;
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0*|-0*)
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set -- "$1" "$(printf '%d' "$2")"
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;;
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*)
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return 1
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;;
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esac
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eval "$1=\"\$2\""
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}
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### Usage: is_bit_set number bit_pos
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###
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### Checks whether the bit at position bit_pos is set.
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###
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### Arguments:
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### number - integer value to extract the bit from
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### bit_pos - bit position (0 = least significant bit)
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###
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### Result:
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### The return 0 (true) if bit is set, 1 (false) if not.
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###
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is_bit_set()
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{
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return $(( !(($1 >> $2) & 1) ))
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}
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### Usage: get_bit result_var number bit_pos
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###
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### Extract the value of the specified bit from a number.
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###
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### Arguments:
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### result_var - name of the variable to store the result
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### number - integer value to extract the bit from
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### bit_pos - bit position (0 = least significant bit)
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###
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### Result:
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### The value of the specified bit (0 or 1) is stored in result_var.
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###
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get_bit()
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{
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is_bit_set "$2" "$3" &&
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eval "$1=1" ||
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eval "$1=0"
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}
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### Usage: set_bit_value result_var number bit value
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###
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### Sets the specified bit in a number to a given value (0 or 1).
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###
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### Arguments:
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### result_var - name of the variable to store the result
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### number - integer value to modify
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### bit - bit position (0 = least significant bit)
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### value - desired bit value (0 or 1)
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###
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### Result:
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### The modified number with the updated bit is stored in result_var.
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###
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set_bit_value()
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{
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local set_bit_value=''
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__set_bit_value() {
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local v
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__shell_prepare_integer v "$1"
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if [ "$3" -eq 0 ]; then
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set_bit_value=$(( $v & ~(1 << $2) ))
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else
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set_bit_value=$(( $v | (1 << $2) ))
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fi
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}
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__set_bit_value "$2" "$3" "$4"
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unset -f __set_bit_value
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eval "$1=\"\$set_bit_value\""
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}
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### Usage: set_bit result_var number bit
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###
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### Sets the specified bit to 1.
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###
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### Arguments:
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### result_var - name of the variable to store the result
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### number - integer value to modify
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### bit - bit position (0 = least significant bit)
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###
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### Result:
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### The modified number with the bit set to 1 is stored in result_var.
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###
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set_bit()
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{
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set_bit_value "$1" "$2" "$3" 1
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}
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### Usage: clear_bit result_var number bit
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###
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### Clears (sets to 0) the specified bit.
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###
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### Arguments:
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### result_var - name of the variable to store the result
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### number - integer value to modify
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### bit - bit position (0 = least significant bit)
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###
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### Result:
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### The modified number with the bit cleared is stored in result_var.
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###
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clear_bit()
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{
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set_bit_value "$1" "$2" "$3" 0
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}
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### Usage: toggle_bit result_var number bit
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###
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### Toggles (inverts) the specified bit.
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###
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### Arguments:
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### result_var - name of the variable to store the result
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### number - integer value to modify
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### bit - bit position (0 = least significant bit)
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###
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### Result:
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### The modified number with the bit inverted is stored in result_var.
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###
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toggle_bit()
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{
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if is_bit_set "$2" "$3"; then
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set_bit_value "$1" "$2" "$3" 0
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else
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set_bit_value "$1" "$2" "$3" 1
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fi
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}
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### Usage: set_bits result_var number bit1 bit2 ...
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###
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### Sets multiple bits to 1 in a number.
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###
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### Arguments:
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### result_var - name of the variable to store the result
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### number - integer value to modify
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### bit1...N - list of bit positions to set
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###
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### Result:
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### The modified number with all specified bits set to 1 is stored in result_var.
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###
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set_bits()
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{
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local __res="$1" number="$2"
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shift 2
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while [ "$#" -gt 0 ]; do
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set_bit_value number "$number" "$1" 1
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shift
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done
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eval "$__res=\"\$number\""
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}
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### Usage: clear_bits result_var number bit1 bit2 ...
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###
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### Clears (sets to 0) multiple bits in a number.
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###
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### Arguments:
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### result_var - name of the variable to store the result
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### number - integer value to modify
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### bit1...N - list of bit positions to clear
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###
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### Result:
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### The modified number with all specified bits cleared is stored in result_var.
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###
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clear_bits()
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{
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local __res="$1" number="$2"
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shift 2
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while [ "$#" -gt 0 ]; do
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set_bit_value number "$number" "$1" 0
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shift
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done
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eval "$__res=\"\$number\""
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}
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### Usage: toggle_bits result_var number bit1 bit2 ...
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###
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### Toggles (inverts) multiple bits in a number.
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###
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### Arguments:
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### result_var - name of the variable to store the result
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### number - integer value to modify
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### bit1...N - list of bit positions to toggle
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###
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### Result:
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### The modified number with all specified bits inverted is stored in result_var.
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###
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toggle_bits()
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{
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printf -v "$__res" '%d' "$number"
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local __res="$1" number="$2"
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shift 2
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while [ "$#" -gt 0 ]; do
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toggle_bit number "$number" "$1"
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shift
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done
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eval "$__res=\"\$number\""
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}
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integer_to_binary()
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{
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local arg
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__shell_prepare_integer arg "$1" ||
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return 1
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set -- "$arg" "$(( ${2:-8} - 1 ))" ""
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while [ $2 -ge 0 ]; do
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set -- "$1" "$(( $2 - 1 ))" "$3$(( ($1 >> $2) & 1 ))"
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done
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printf '%s\n' "$3"
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}
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fi #__included_shell_bits

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