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v/vlib/bitfield/bitfield.v

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