shell-bitwise

#!/bin/sh -efu
### This file is covered by the GNU General Public License,
### which should be included with libshell as the file LICENSE.
### All copyright information are listed in the COPYING.

if [ -z "${__included_shell_bits-}" ]; then
__included_shell_bits=1

__shell_prepare_integer()
{
	case "$2" in
		9223372036854775808|-9223372036854775808|0[xX]8000000000000000|-0[xX]8000000000000000)
			set -- "$1" "(0x7fffffffffffffff + 1)"
			;;
		0[xX][0-9A-Fa-f]*|[1-9]*|-[1-9]*)
			;;
		-0[xX]*)
			return 1
			;;
		0*|-0*)
			set -- "$1" "$(printf '%d' "$2")"
			;;
		*)
			return 1
			;;
	esac
	eval "$1=\"\$2\""
}

### Usage: is_bit_set number bit_pos
###
### Checks whether the bit at position bit_pos is set.
###
### Arguments:
###   number     - integer value to extract the bit from
###   bit_pos    - bit position (0 = least significant bit)
###
### Result:
###   The return 0 (true) if bit is set, 1 (false) if not.
###
is_bit_set()
{
	return $(( !(($1 >> $2) & 1) ))
}

### Usage: get_bit result_var number bit_pos
###
### Extract the value of the specified bit from a number.
###
### Arguments:
###   result_var - name of the variable to store the result
###   number     - integer value to extract the bit from
###   bit_pos    - bit position (0 = least significant bit)
###
### Result:
###   The value of the specified bit (0 or 1) is stored in result_var.
###
get_bit()
{
	is_bit_set "$2" "$3" &&
		eval "$1=1" ||
		eval "$1=0"
}

### Usage: set_bit_value result_var number bit value
###
### Sets the specified bit in a number to a given value (0 or 1).
###
### Arguments:
###   result_var - name of the variable to store the result
###   number     - integer value to modify
###   bit        - bit position (0 = least significant bit)
###   value      - desired bit value (0 or 1)
###
### Result:
###   The modified number with the updated bit is stored in result_var.
###
set_bit_value()
{
	local set_bit_value=''
	__set_bit_value() {
		local v
		__shell_prepare_integer v "$1"
		if [ "$3" -eq 0 ]; then
			set_bit_value=$(( $v & ~(1 << $2) ))
		else
			set_bit_value=$(( $v | (1 << $2) ))
		fi
	}
	__set_bit_value "$2" "$3" "$4"
	unset -f __set_bit_value
	eval "$1=\"\$set_bit_value\""
}

### Usage: set_bit result_var number bit
###
### Sets the specified bit to 1.
###
### Arguments:
###   result_var - name of the variable to store the result
###   number     - integer value to modify
###   bit        - bit position (0 = least significant bit)
###
### Result:
###   The modified number with the bit set to 1 is stored in result_var.
###
set_bit()
{
	set_bit_value "$1" "$2" "$3" 1
}

### Usage: clear_bit result_var number bit
###
### Clears (sets to 0) the specified bit.
###
### Arguments:
###   result_var - name of the variable to store the result
###   number     - integer value to modify
###   bit        - bit position (0 = least significant bit)
###
### Result:
###   The modified number with the bit cleared is stored in result_var.
###
clear_bit()
{
	set_bit_value "$1" "$2" "$3" 0
}

### Usage: toggle_bit result_var number bit
###
### Toggles (inverts) the specified bit.
###
### Arguments:
###   result_var - name of the variable to store the result
###   number     - integer value to modify
###   bit        - bit position (0 = least significant bit)
###
### Result:
###   The modified number with the bit inverted is stored in result_var.
###
toggle_bit()
{
	if is_bit_set "$2" "$3"; then
		set_bit_value "$1" "$2" "$3" 0
	else
		set_bit_value "$1" "$2" "$3" 1
	fi
}

### Usage: set_bits result_var number bit1 bit2 ...
###
### Sets multiple bits to 1 in a number.
###
### Arguments:
###   result_var - name of the variable to store the result
###   number     - integer value to modify
###   bit1...N   - list of bit positions to set
###
### Result:
###   The modified number with all specified bits set to 1 is stored in result_var.
###
set_bits()
{
	local __res="$1" number="$2"
	shift 2
	while [ "$#" -gt 0 ]; do
		set_bit_value number "$number" "$1" 1
		shift
	done
	eval "$__res=\"\$number\""
}

### Usage: clear_bits result_var number bit1 bit2 ...
###
### Clears (sets to 0) multiple bits in a number.
###
### Arguments:
###   result_var - name of the variable to store the result
###   number     - integer value to modify
###   bit1...N   - list of bit positions to clear
###
### Result:
###   The modified number with all specified bits cleared is stored in result_var.
###
clear_bits()
{
	local __res="$1" number="$2"
	shift 2
	while [ "$#" -gt 0 ]; do
		set_bit_value number "$number" "$1" 0
		shift
	done
	eval "$__res=\"\$number\""
}

### Usage: toggle_bits result_var number bit1 bit2 ...
###
### Toggles (inverts) multiple bits in a number.
###
### Arguments:
###   result_var - name of the variable to store the result
###   number     - integer value to modify
###   bit1...N   - list of bit positions to toggle
###
### Result:
###   The modified number with all specified bits inverted is stored in result_var.
###
toggle_bits()
{
	printf -v "$__res" '%d' "$number"
	local __res="$1" number="$2"
	shift 2
	while [ "$#" -gt 0 ]; do
		toggle_bit number "$number" "$1"
		shift
	done
	eval "$__res=\"\$number\""
}

integer_to_binary()
{
	local arg

	__shell_prepare_integer arg "$1" ||
		return 1

	set -- "$arg" "$(( ${2:-8} - 1 ))" ""

	while [ $2 -ge 0 ]; do
		set -- "$1" "$(( $2 - 1 ))" "$3$(( ($1 >> $2) & 1 ))"
	done

	printf '%s\n' "$3"
}

fi #__included_shell_bits