The bitsarr package facilitates manipulation of arrays of bits in a Big-Endian manner. It enables creation, setting, and retrieval of individual bits within an array, along with generating binary string representations.

bitarr.go

package bitsarr

import (
	"bytes"
	"errors"
)

type bit byte

const (
	Zero bit = 0
	One  bit = 1
)

// Struct to represent an array of bits of arbitrary length
// Big-Endian way
type BitArray struct {
	data []byte
	bits int
}

// Create and initialize a new BitArray instance with the specified number of bits
func NewBitArray(bits int) (*BitArray, error) {
	if bits <= 0 {
		return nil, errors.New("invalid number of bits")
	}

	size := (bits + 7) / 8

	data := make([]byte, size)

	return &BitArray{
		data: data,
		bits: bits,
	}, nil
}

// SetBit sets the bit at the specified index to the given value (Zero or One)
func (u *BitArray) SetBit(index int, value bit) error {
	if index < 0 || index >= u.bits {
		return errors.New("index out of range")
	}

	byteIndex := (u.bits - index - 1) / 8
	bitIndex := uint(7 - ((u.bits - index - 1) % 8))

	// Clear the target bit and set it to the new value
	if value == Zero {
		u.data[byteIndex] &^= (1 << bitIndex)
	} else {
		u.data[byteIndex] |= (1 << bitIndex)
	}

	return nil
}

// GetBit returns the value of the bit at the specified index (Zero or One)
func (u *BitArray) GetBit(index int) (int, error) {
	if index < 0 || index >= u.bits {
		return -1, errors.New("index out of range")
	}

	byteIndex := (u.bits - index - 1) / 8
	bitIndex := uint(7 - ((u.bits - index - 1) % 8))

	bit := (u.data[byteIndex] >> bitIndex) & 1

	return int(bit), nil
}

// String returns a binary string representation of the BitArray instance
func (u BitArray) String() string {
	var buf bytes.Buffer
	for i := 0; i < u.bits; i++ {
		bit, _ := u.GetBit(i)
		buf.WriteByte(byte('0' + bit))
	}
	return buf.String()
}