466 lines
12 KiB
V
466 lines
12 KiB
V
module bitfield
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/*
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bitfield is a module for
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manipulating arrays of bits, i.e. series of zeroes and ones spread across an
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array of storage units (unsigned 32-bit integers).
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BitField structure
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------------------
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Bit arrays are stored in data structures called 'BitField'. The structure is
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'opaque', i.e. its internals are not available to the end user. This module
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provides API (functions and methods) for accessing and modifying bit arrays.
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*/
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pub struct BitField {
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mut:
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size int
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//field *u32
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field []u32
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}
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// helper functions
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const (
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slot_size = 32
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)
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// public functions
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// from_bytes() converts a byte array into a bitfield.
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pub fn from_bytes(input []byte) BitField {
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mut output := new(input.len * 8)
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for i, b in input {
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output.field[i / 4] |= u32(b) << ((i % 4) * 8)
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}
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return output
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}
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// from_str converts a string of characters ('0' and '1') to a bit
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// array. Any character different from '0' is treated as '1'.
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pub fn from_str(input string) BitField {
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mut output := new(input.len)
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for i in 0..input.len {
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if input[i] != `0` {
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output.set_bit(i)
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}
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}
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return output
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}
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// str converts the bit array to a string of characters ('0' and '1') and
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// return the string
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pub fn (input BitField) str() string {
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mut output := ''
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for i in 0..input.size {
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if input.get_bit(i) == 1 {
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output = output + '1'
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}
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else {
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output = output + '0'
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}
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}
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return output
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}
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// new creates an empty bit array of capable of storing 'size' bits.
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pub fn new(size int) BitField {
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output := BitField{
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size: size
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//field: *u32(calloc(bitnslots(size) * slot_size / 8))
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field: []u32{len:bitnslots(size)}
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}
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return output
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}
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/*
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pub fn del(instance *BitField) {
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free(instance.field)
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free(instance)
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}
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*/
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// get_bit returns the value (0 or 1) of bit number 'bit_nr' (count from 0).
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pub fn (instance BitField) get_bit(bitnr int) int {
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if bitnr >= instance.size {
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return 0
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}
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return int((instance.field[bitslot(bitnr)] >> (bitnr % slot_size)) & u32(1))
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}
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// set_bit sets bit number 'bit_nr' to 1 (count from 0).
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pub fn (mut instance BitField) set_bit(bitnr int) {
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if bitnr >= instance.size {
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return
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}
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instance.field[bitslot(bitnr)] |= bitmask(bitnr)
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}
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// clear_bit clears (sets to zero) bit number 'bit_nr' (count from 0).
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pub fn (mut instance BitField) clear_bit(bitnr int) {
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if bitnr >= instance.size {
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return
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}
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instance.field[bitslot(bitnr)] &= ~bitmask(bitnr)
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}
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// set_all sets all bits in the array to 1.
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pub fn (mut instance BitField) set_all() {
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for i in 0..bitnslots(instance.size) {
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instance.field[i] = u32(-1)
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}
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instance.clear_tail()
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}
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// clear_all clears (sets to zero) all bits in the array.
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pub fn (mut instance BitField) clear_all() {
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for i in 0..bitnslots(instance.size) {
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instance.field[i] = u32(0)
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}
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}
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// toggle_bit changes the value (from 0 to 1 or from 1 to 0) of bit
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// number 'bit_nr'.
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pub fn (mut instance BitField) toggle_bit(bitnr int) {
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if bitnr >= instance.size {
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return
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}
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instance.field[bitslot(bitnr)] ^= bitmask(bitnr)
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}
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// bf_and performs logical AND operation on every pair of bits from 'input1' and
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// 'input2' and returns the result as a new array. If inputs differ in size,
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// the tail of the longer one is ignored.
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pub fn bf_and(input1 BitField, input2 BitField) BitField {
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size := min(input1.size, input2.size)
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bitnslots := bitnslots(size)
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mut output := new(size)
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for i in 0..bitnslots {
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output.field[i] = input1.field[i] & input2.field[i]
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}
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output.clear_tail()
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return output
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}
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// bf_not toggles all bits in a bit array and returns the result as a new array.
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pub fn bf_not(input BitField) BitField {
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size := input.size
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bitnslots := bitnslots(size)
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mut output := new(size)
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for i in 0..bitnslots {
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output.field[i] = ~input.field[i]
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}
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output.clear_tail()
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return output
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}
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// bf_or performs logical OR operation on every pair of bits from 'input1' and
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// 'input2' and returns the result as a new array. If inputs differ in size,
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// the tail of the longer one is ignored.
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pub fn bf_or(input1 BitField, input2 BitField) BitField {
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size := min(input1.size, input2.size)
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bitnslots := bitnslots(size)
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mut output := new(size)
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for i in 0..bitnslots {
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output.field[i] = input1.field[i] | input2.field[i]
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}
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output.clear_tail()
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return output
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}
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// bf_xor perform logical XOR operation on every pair of bits from 'input1' and
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// 'input2' and returns the result as a new array. If inputs differ in size,
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// the tail of the longer one is ignored.
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pub fn bf_xor(input1 BitField, input2 BitField) BitField {
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size := min(input1.size, input2.size)
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bitnslots := bitnslots(size)
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mut output := new(size)
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for i in 0..bitnslots {
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output.field[i] = input1.field[i] ^ input2.field[i]
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}
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output.clear_tail()
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return output
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}
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// join concatenates two bit arrays and return the result as a new array.
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pub fn join(input1 BitField, input2 BitField) BitField {
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output_size := input1.size + input2.size
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mut output := new(output_size)
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// copy the first input to output as is
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for i in 0..bitnslots(input1.size) {
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output.field[i] = input1.field[i]
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}
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// find offset bit and offset slot
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offset_bit := input1.size % slot_size
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offset_slot := input1.size / slot_size
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for i in 0..bitnslots(input2.size) {
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output.field[i + offset_slot] |=
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u32(input2.field[i] << u32(offset_bit))
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}
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/*
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* If offset_bit is not zero, additional operations are needed.
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* Number of iterations depends on the nr of slots in output. Two
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* options:
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* (a) nr of slots in output is the sum of inputs' slots. In this
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* case, the nr of bits in the last slot of output is less than the
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* nr of bits in the second input (i.e. ), OR
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* (b) nr of slots of output is the sum of inputs' slots less one
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* (i.e. less iterations needed). In this case, the nr of bits in
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* the last slot of output is greater than the nr of bits in the second
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* input.
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* If offset_bit is zero, no additional copies needed.
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*/
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if (output_size - 1) % slot_size < (input2.size - 1) % slot_size {
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for i in 0..bitnslots(input2.size) {
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output.field[i + offset_slot + 1] |=
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u32(input2.field[i] >> u32(slot_size - offset_bit))
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}
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} else if (output_size - 1) % slot_size > (input2.size - 1) % slot_size {
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for i in 0..bitnslots(input2.size) - 1 {
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output.field[i + offset_slot + 1] |=
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u32(input2.field[i] >> u32(slot_size - offset_bit))
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}
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}
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return output
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}
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// get_size returns the number of bits the array can hold.
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pub fn (instance BitField) get_size() int {
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return instance.size
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}
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// clone creates a copy of a bit array.
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pub fn (instance BitField) clone() BitField {
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bitnslots := bitnslots(instance.size)
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mut output := new(instance.size)
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for i in 0..bitnslots {
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output.field[i] = instance.field[i]
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}
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return output
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}
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// cmp compares two bit arrays bit by bit and returns 'true' if they are
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// identical by length and contents and 'false' otherwise.
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pub fn (instance BitField) cmp(input BitField) bool {
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if instance.size != input.size {return false}
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for i in 0..bitnslots(instance.size) {
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if instance.field[i] != input.field[i] {return false}
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}
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return true
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}
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// pop_count returns the number of set bits (ones) in the array.
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pub fn (instance BitField) pop_count() int {
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size := instance.size
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bitnslots := bitnslots(size)
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tail := size % slot_size
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mut count := 0
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for i in 0..bitnslots - 1 {
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for j in 0..slot_size {
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if u32(instance.field[i] >> u32(j)) & u32(1) == u32(1) {
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count++
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}
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}
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}
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for j in 0..tail {
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if u32(instance.field[bitnslots - 1] >> u32(j)) & u32(1) == u32(1) {
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count++
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}
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}
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return count
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}
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// hamming computes the Hamming distance between two bit arrays.
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pub fn hamming(input1 BitField, input2 BitField) int {
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input_xored := bf_xor(input1, input2)
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return input_xored.pop_count()
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}
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// pos checks if the array contains a sub-array 'needle' and returns its
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// position if it does, -1 if it does not, and -2 on error.
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pub fn (haystack BitField) pos(needle BitField) int {
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heystack_size := haystack.size
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needle_size := needle.size
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diff := heystack_size - needle_size
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// needle longer than haystack; return error code -2
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if diff < 0 {
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return -2
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}
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for i := 0; i <= diff; i++ {
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needle_candidate := haystack.slice(i, needle_size + i)
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if needle_candidate.cmp(needle) {
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// needle matches a sub-array of haystack; return starting position of the sub-array
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return i
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}
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}
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// nothing matched; return -1
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return -1
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}
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// slice returns a sub-array of bits between 'start_bit_nr' (included) and
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// 'end_bit_nr' (excluded).
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pub fn (input BitField) slice(_start int, _end int) BitField {
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// boundary checks
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mut start := _start
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mut end := _end
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if end > input.size {
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end = input.size // or panic?
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}
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if start > end {
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start = end // or panic?
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}
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mut output := new(end - start)
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start_offset := start % slot_size
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end_offset := (end - 1) % slot_size
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start_slot := start / slot_size
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end_slot := (end - 1) / slot_size
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output_slots := bitnslots(end - start)
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if output_slots > 1 {
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if start_offset != 0 {
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for i in 0..output_slots - 1 {
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output.field[i] =
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u32(input.field[start_slot + i] >> u32(start_offset))
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output.field[i] = output.field[i] |
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u32(input.field[start_slot + i + 1] <<
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u32(slot_size - start_offset))
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}
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}
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else {
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for i in 0..output_slots - 1 {
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output.field[i] =
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u32(input.field[start_slot + i])
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}
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}
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}
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if start_offset > end_offset {
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output.field[(end - start - 1) / slot_size] =
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u32(input.field[end_slot - 1] >> u32(start_offset))
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mut mask := u32((1 << (end_offset + 1)) - 1)
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mask = input.field[end_slot] & mask
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mask = u32(mask << u32(slot_size - start_offset))
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output.field[(end - start - 1) / slot_size] |= mask
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}
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else if start_offset == 0 {
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mut mask := u32(0)
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if end_offset == slot_size - 1 {
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mask = u32(-1)
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}
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else {
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mask = u32(u32(1) << u32(end_offset + 1))
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mask = mask - u32(1)
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}
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output.field[(end - start - 1) / slot_size] =
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(input.field[end_slot] & mask)
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}
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else {
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mut mask := u32(((1 << (end_offset - start_offset + 1)) - 1) << start_offset)
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mask = input.field[end_slot] & mask
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mask = u32(mask >> u32(start_offset))
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output.field[(end - start - 1) / slot_size] |= mask
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}
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return output
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}
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// reverse reverses the order of bits in the array (swap the first with the
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// last, the second with the last but one and so on).
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pub fn (instance BitField) reverse() BitField {
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size := instance.size
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bitnslots := bitnslots(size)
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mut output := new(size)
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for i:= 0; i < (bitnslots - 1); i++ {
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for j in 0..slot_size {
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if u32(instance.field[i] >> u32(j)) & u32(1) == u32(1) {
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output.set_bit(size - i * slot_size - j - 1)
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}
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}
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}
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bits_in_last_input_slot := (size - 1) % slot_size + 1
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for j in 0..bits_in_last_input_slot {
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if u32(instance.field[bitnslots - 1] >> u32(j)) & u32(1) == u32(1) {
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output.set_bit(bits_in_last_input_slot - j - 1)
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}
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}
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return output
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}
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// resize changes the size of the bit array to 'new_size'.
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pub fn (mut instance BitField) resize(new_size int) {
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new_bitnslots := bitnslots(new_size)
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old_size := instance.size
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old_bitnslots := bitnslots(old_size)
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mut field := []u32{len:new_bitnslots}
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for i := 0; i < old_bitnslots && i < new_bitnslots; i++ {
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field[i] = instance.field[i]
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}
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instance.field = field.clone()
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instance.size = new_size
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if new_size < old_size && new_size % slot_size != 0 {
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instance.clear_tail()
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}
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}
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// rotate circular-shifts the bits by 'offset' positions (move
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// 'offset' bit to 0, 'offset+1' bit to 1, and so on).
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pub fn (instance BitField) rotate(offset int) BitField {
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/**
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* This function "cuts" the bitfield into two and swaps them.
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* If the offset is positive, the cutting point is counted from the
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* beginning of the bit array, otherwise from the end.
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**/
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size := instance.size
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// removing extra rotations
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mut offset_internal := offset % size
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if offset_internal == 0 {
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// nothing to shift
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return instance
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}
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if offset_internal < 0 {
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offset_internal = offset_internal + size
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}
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first_chunk := instance.slice(0, offset_internal)
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second_chunk := instance.slice(offset_internal, size)
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output := join(second_chunk, first_chunk)
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return output
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}
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// Internal functions
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fn (mut instance BitField) clear_tail() {
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tail := instance.size % slot_size
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if tail != 0 {
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// create a mask for the tail
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mask := u32((1 << tail) - 1)
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// clear the extra bits
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instance.field[bitnslots(instance.size) - 1] = instance.field[bitnslots(instance.size) - 1] & mask
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}
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}
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fn bitmask(bitnr int) u32 {
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return u32(u32(1) << u32(bitnr % slot_size))
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}
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fn bitslot(size int) int {
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return size / slot_size
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}
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fn min(input1 int, input2 int) int {
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if input1 < input2 {
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return input1
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}
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else {
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return input2
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}
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}
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fn bitnslots(length int) int {
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return (length - 1) / slot_size + 1
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}
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