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use super::BitIterator;
use super::Bitwise;
/**
* Arithmetic operations implementation for `[u8]`
*/
pub trait BitArith {
type Other: ?Sized;
/// Comparison for big-endian
/// # Examples
/// ```
/// # use nbits::core::BitArith;
/// # use std::cmp::Ordering;
/// assert_eq!([0b0011_0011, 0b0011_0011].bit_be_cmp(&[0b1111_1111]), Ordering::Greater);
/// assert_eq!([0b0000_0000, 0b0011_0011].bit_be_cmp(&[0b1111_1111]), Ordering::Less);
/// assert_eq!([0b0011_0011, 0b0011_0011].bit_be_cmp(&[0b0000_0000, 0b1111_1111]), Ordering::Greater);
/// assert_eq!([0b0011_0011, 0b0011_0011].bit_be_cmp(&[0b1111_1111, 0b0000_0000]), Ordering::Less);
/// ```
fn bit_be_cmp(&self, other: &Self) -> std::cmp::Ordering;
/// Bit arithmetic operator `+=` for big-endian
/// # Example
/// ```
/// # use nbits::core::BitArith;
/// let (mut a, b) = ([0b1100_1100, 0b1000_0001], [0b1000_0001]);
/// assert_eq!(a.as_mut().bit_be_add(&b), false);
/// assert_eq!(a, [0b1100_1101, 0b0000_0010]);
/// ```
fn bit_be_add(&mut self, other: &Self::Other) -> bool;
/// Bit arithmetic operator `-=` for big-endian
/// # Example
/// ```
/// # use nbits::core::BitArith;
/// let (mut a, b) = ([0b1100_1100, 0b1000_0001], [0b1000_0001]);
/// assert_eq!(a.as_mut().bit_be_sub(&b), false);
/// assert_eq!(a, [0b1100_1100, 0b0000_0000]);
/// ```
fn bit_be_sub(&mut self, other: &Self::Other) -> bool;
/// Bit arithmetic operator `*=` for big-endian
/// # Example
/// ```
/// # use nbits::core::BitArith;
/// let (mut a, b) = ([0b0011_0000, 0b1000_0001], [0b0000_0010]);
/// assert_eq!(a.as_mut().bit_be_mul(&b), false);
/// assert_eq!(a, [0b0110_0001, 0b0000_0010]);
/// ```
fn bit_be_mul(&mut self, other: &Self::Other) -> bool;
/// Bit arithmetic operator `/=` for big-endian
/// # Example
/// ```
/// # use nbits::core::BitArith;
/// let (a, b) = ([0b1100_0011, 0b0000_0001], [0b1000_0001]);
/// let mut x = a.clone();
/// x.as_mut().bit_be_div(&b);
/// assert_eq!(x, (u16::from_be_bytes(a) / u16::from_be_bytes([0, b[0]])).to_be_bytes());
/// ```
fn bit_be_div(&mut self, other: &Self::Other) -> bool;
/// Bit arithmetic operator `%=` for big-endian
/// # Example
/// ```
/// # use nbits::core::BitArith;
/// let (a, b) = ([0b1100_0011, 0b0000_0001], [0b0000_0001, 0b1000_0001]);
/// let mut x = a.clone();
/// x.as_mut().bit_be_rem(&b);
/// // assert_eq!(x, (u16::from_be_bytes(a) % u16::from_be_bytes(b)).to_be_bytes());
/// ```
fn bit_be_rem(&mut self, other: &Self::Other) -> bool;
}
impl BitArith for [u8] {
type Other = Self;
fn bit_be_cmp(&self, other: &Self) -> std::cmp::Ordering {
let max_len = std::cmp::max(self.len(), other.len());
self.extend_be_iter(max_len)
.cmp(other.extend_be_iter(max_len))
}
fn bit_be_add(&mut self, other: &Self) -> bool {
self.iter_mut()
.rev()
.zip(other.iter().rev().chain(std::iter::repeat(&0)))
.fold(false, |mut carry, (a, b)| {
match (carry, *b) {
(true, 0xff) => carry = true,
(true, _) => (*a, carry) = a.overflowing_add(b + 1),
(false, _) => (*a, carry) = a.overflowing_add(*b),
};
carry
})
}
fn bit_be_sub(&mut self, other: &Self) -> bool {
self.iter_mut()
.rev()
.zip(other.iter().rev().chain(std::iter::repeat(&0)))
.fold(false, |mut borrow, (a, b)| {
match (borrow, *b) {
(true, 0xff) => borrow = true,
(true, _) => (*a, borrow) = a.overflowing_sub(b + 1),
(false, _) => (*a, borrow) = a.overflowing_sub(*b),
};
borrow
})
}
fn bit_be_mul(&mut self, other: &Self) -> bool {
let mut result = vec![0; self.len()];
let mut overflow = false;
for (i, bit) in other.bit_iter().rev().enumerate() {
if bit {
let mut multiple = self.to_vec();
overflow |= multiple.bit_shl(i);
overflow |= result.bit_be_add(&multiple);
}
}
self.copy_from_slice(&result);
overflow
}
fn bit_be_div(&mut self, other: &Self) -> bool {
if other.iter().all(|&b| b == 0) {
return true; // Division by zero, return overflow
}
// Ignore leading zeros
let bits_a = self.len() * 8 - self.bit_leading_zeros(); // effective bits length
let bits_b = other.len() * 8 - other.bit_leading_zeros(); // effective bits length
if bits_a < bits_b {
self.fill(0);
return false;
}
let mut other = other.extend_be(self.len()); // extend to the same length
{
// Remove common trailing zeros
let common_divisor_bits = self.bit_trailing_zeros().min(other.bit_trailing_zeros());
self.bit_shr(common_divisor_bits);
other.bit_shr(common_divisor_bits);
}
// Perform division
let n = self.len();
let mut result = vec![0; n];
let diff = bits_a - bits_b;
other.bit_shl(diff);
for i in (0..=diff).rev() {
if self.bit_be_cmp(&other) != std::cmp::Ordering::Less {
self.bit_be_sub(&other);
result[n - 1 - i / 8] |= 1 << (i % 8);
}
other.bit_shr(1);
}
self.copy_from_slice(&result);
false
}
fn bit_be_rem(&mut self, other: &Self) -> bool {
if other.iter().all(|&b| b == 0) {
return true; // Division by zero, return overflow
}
// Ignore leading zeros
let bits_a = self.len() * 8 - self.bit_leading_zeros(); // effective bits length
let bits_b = other.len() * 8 - other.bit_leading_zeros(); // effective bits length
if bits_a < bits_b {
return false;
}
let mut other = other.extend_be(self.len()); // extend to the same length
{
// Remove common trailing zeros
let common_divisor_bits = self.bit_trailing_zeros().min(other.bit_trailing_zeros());
self.bit_shr(common_divisor_bits);
other.bit_shr(common_divisor_bits);
}
// Perform division
let n = self.len();
let mut result = vec![0; n];
let diff = bits_a - bits_b;
other.bit_shl(diff);
for i in (0..=diff).rev() {
if self.bit_be_cmp(&other) != std::cmp::Ordering::Less {
self.bit_be_sub(&other);
result[n - 1 - i / 8] |= 1 << (i % 8);
}
other.bit_shr(1);
}
false
}
}
trait ByteExtend {
fn extend_be_iter(&self, n: usize) -> impl DoubleEndedIterator<Item = &u8>;
fn extend_be(&self, n: usize) -> Vec<u8>;
}
impl ByteExtend for [u8] {
#[inline(always)]
fn extend_be_iter(&self, n: usize) -> impl DoubleEndedIterator<Item = &u8> {
std::iter::repeat_n(&0, n - self.len()).chain(self.iter())
}
#[inline(always)]
fn extend_be(&self, n: usize) -> Vec<u8> {
let mut data = vec![0; n];
if self.len() < n {
data[n - self.len()..].copy_from_slice(self);
} else {
assert!(self[..self.len() - n].iter().all(|&b| b == 0));
data.copy_from_slice(&self[self.len() - n..]);
}
data
}
}
#[cfg(test)]
mod test_arith {
use super::*;
#[test]
fn test_bits_add() {
let mut a = [0b1111_1111, 0b1111_1111];
assert_eq!(a.bit_be_add(&[0b0000_0001]), true);
assert_eq!(a, [0b0000_0000, 0b0000_0000]);
let mut a = [0b0000_0000, 0b0000_0001];
assert_eq!(a.bit_be_add(&[0b1111_1111]), false);
assert_eq!(a, [0b0000_0001, 0b0000_0000]);
}
#[test]
fn test_bits_sub() {
let mut a = [0b0000_0000, 0b0000_0001];
assert_eq!(a.bit_be_sub(&[0b1111_1111]), true);
assert_eq!(a, [0b1111_1111, 0b0000_0010]);
let mut a = [0b1111_1111, 0b0000_0000];
assert_eq!(a.bit_be_sub(&[0b0000_0001]), false);
assert_eq!(a, [0b1111_1110, 0b1111_1111]);
}
#[test]
fn test_bits_mul() {
let mut a = [0xff, 0xff];
assert_eq!(a.bit_be_mul(&[0b0000_0010]), true);
assert_eq!(a, [0b1111_1111, 0b1111_1110]);
let mut a = [0b0000_0001, 0b0000_0001];
assert_eq!(a.bit_be_mul(&[0b1111_1111]), false);
assert_eq!(a, [0b1111_1111, 0b1111_1111]);
}
pub trait BeValue {
fn value(&self) -> u64;
}
impl BeValue for [u8] {
fn value(&self) -> u64 {
let mut bytes = [0; 8];
bytes[8 - self.len()..].copy_from_slice(self);
u64::from_be_bytes(bytes)
}
}
#[test]
fn test_bits_div() {
const TDATA: &[(&[u8], &[u8], &[u8])] = &[
(&[0b0000_1100], &[0b0000_0011], &[0b0000_0100]),
(&[0b0011_0000, 0], &[0b0000_1100], &[0b0000_0100, 0]),
(&[0b1100_1100], &[0, 0b0000_0011], &[0b0100_0100]),
];
for (a, b, c) in TDATA {
assert_eq!(a.value() / b.value(), c.value());
let mut a = a.to_vec();
assert_eq!(a.bit_be_div(b), false);
assert_eq!(&a, c);
}
}
}