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use num::basic::unsigneds::PrimitiveUnsigned;
use num::conversion::traits::{CheckedFrom, PowerOf2Digits, WrappingFrom};
fn to_power_of_2_digits_asc<T: PrimitiveUnsigned, U: PrimitiveUnsigned + WrappingFrom<T>>(
x: &T,
log_base: u64,
) -> Vec<U> {
assert_ne!(log_base, 0);
if log_base > U::WIDTH {
panic!(
"type {:?} is too small for a digit of width {}",
U::NAME,
log_base
);
}
let mut digits = Vec::new();
if *x == T::ZERO {
} else if x.significant_bits() <= log_base {
digits.push(U::wrapping_from(*x));
} else {
let mut x = *x;
let mask = U::low_mask(log_base);
while x != T::ZERO {
digits.push(U::wrapping_from(x) & mask);
x >>= log_base;
}
}
digits
}
fn to_power_of_2_digits_desc<T: PrimitiveUnsigned, U: PrimitiveUnsigned + WrappingFrom<T>>(
x: &T,
log_base: u64,
) -> Vec<U> {
let mut digits = to_power_of_2_digits_asc(x, log_base);
digits.reverse();
digits
}
fn from_power_of_2_digits_asc<
T: CheckedFrom<U> + PrimitiveUnsigned + WrappingFrom<U>,
U: PrimitiveUnsigned,
I: Iterator<Item = U>,
>(
log_base: u64,
digits: I,
) -> Option<T> {
assert_ne!(log_base, 0);
if log_base > U::WIDTH {
panic!(
"type {:?} is too small for a digit of width {}",
U::NAME,
log_base
);
}
let mut n = T::ZERO;
let mut shift = 0;
for digit in digits {
if digit.significant_bits() > log_base {
return None;
}
n |= T::checked_from(digit).and_then(|d| d.arithmetic_checked_shl(shift))?;
shift += log_base;
}
Some(n)
}
fn from_power_of_2_digits_desc<
T: PrimitiveUnsigned + WrappingFrom<U>,
U: PrimitiveUnsigned,
I: Iterator<Item = U>,
>(
log_base: u64,
digits: I,
) -> Option<T> {
assert_ne!(log_base, 0);
if log_base > U::WIDTH {
panic!(
"type {:?} is too small for a digit of width {}",
U::NAME,
log_base
);
}
let mut n = T::ZERO;
for digit in digits {
if digit.significant_bits() > log_base {
return None;
}
let shifted = n.arithmetic_checked_shl(log_base)?;
n = shifted | T::wrapping_from(digit);
}
Some(n)
}
macro_rules! impl_power_of_2_digits {
($t:ident) => {
macro_rules! impl_power_of_2_digits_inner {
($u:ident) => {
impl PowerOf2Digits<$u> for $t {
/// Returns a [`Vec`] containing the base-$2^k$ digits of a number in ascending
/// order (least- to most-significant).
///
/// The base-2 logarithm of the base is specified. `log_base` must be no larger
/// than the width of the digit type. If `self` is 0, the [`Vec`] is empty;
/// otherwise, it ends with a nonzero digit.
///
/// $f(x, k) = (d_i)_ {i=0}^{n-1}$, where $0 \leq d_i < 2^k$ for all $i$,
/// $n=0$ or $d_{n-1} \neq 0$, and
///
/// $$
/// \sum_{i=0}^{n-1}2^{ki}d_i = x.
/// $$
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(n)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is
/// `self.significant_bits()`.
///
/// # Panics
/// Panics if `log_base` is greater than the width of the output type, or if
/// `log_base` is zero.
///
/// # Examples
/// See [here](super::power_of_2_digits#to_power_of_2_digits_asc).
#[inline]
fn to_power_of_2_digits_asc(&self, log_base: u64) -> Vec<$u> {
to_power_of_2_digits_asc(self, log_base)
}
/// Returns a [`Vec`] containing the base-$2^k$ digits of a number in
/// descending order (most- to least-significant).
///
/// The base-2 logarithm of the base is specified. `log_base` must be no larger
/// than the width of the digit type. If `self` is 0, the [`Vec`] is empty;
/// otherwise, it begins with a nonzero digit.
///
/// $f(x, k) = (d_i)_ {i=0}^{n-1}$, where $0 \leq d_i < 2^k$ for all $i$,
/// $n=0$ or $d_0 \neq 0$, and
///
/// $$
/// \sum_{i=0}^{n-1}2^{k (n-i-1)}d_i = x.
/// $$
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(n)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is
/// `self.significant_bits()`.
///
/// # Panics
/// Panics if `log_base` is greater than the width of the output type, or if
/// `log_base` is zero.
///
/// # Examples
/// See [here](super::power_of_2_digits#to_power_of_2_digits_desc).
#[inline]
fn to_power_of_2_digits_desc(&self, log_base: u64) -> Vec<$u> {
to_power_of_2_digits_desc(self, log_base)
}
/// Converts an iterator of base-$2^k$ digits into a value.
///
/// The base-2 logarithm of the base is specified. The input digits are in
/// ascending order (least- to most-significant). `log_base` must be no larger
/// than the width of the digit type. The function returns `None` if the input
/// represents a number that can't fit in the output type.
///
/// $$
/// f((d_i)_ {i=0}^{n-1}, k) = \sum_{i=0}^{n-1}2^{ki}d_i.
/// $$
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `digits.count()`.
///
/// # Panics
/// Panics if `log_base` is greater than the width of the digit type, or if
/// `log_base` is zero.
///
/// # Examples
/// See [here](super::power_of_2_digits#from_power_of_2_digits_asc).
#[inline]
fn from_power_of_2_digits_asc<I: Iterator<Item = $u>>(
log_base: u64,
digits: I,
) -> Option<$t> {
from_power_of_2_digits_asc(log_base, digits)
}
/// Converts an iterator of base-$2^k$ digits into a value.
///
/// The base-2 logarithm of the base is specified. The input digits are in
/// descending order (most- to least-significant). `log_base` must be no larger
/// than the width of the digit type. The function returns `None` if the input
/// represents a number that can't fit in the output type.
///
/// $$
/// f((d_i)_ {i=0}^{n-1}, k) = \sum_{i=0}^{n-1}2^{k (n-i-1)}d_i.
/// $$
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `digits.count()`.
///
/// # Panics
/// Panics if `log_base` is greater than the width of the digit type, or if
/// `log_base` is zero.
///
/// # Examples
/// See [here](super::power_of_2_digits#from_power_of_2_digits_desc).
fn from_power_of_2_digits_desc<I: Iterator<Item = $u>>(
log_base: u64,
digits: I,
) -> Option<$t> {
from_power_of_2_digits_desc(log_base, digits)
}
}
};
}
apply_to_unsigneds!(impl_power_of_2_digits_inner);
};
}
apply_to_unsigneds!(impl_power_of_2_digits);