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// Copyright © 2026 Mikhail Hogrefe
//
// This file is part of Malachite.
//
// Malachite is free software: you can redistribute it and/or modify it under the terms of the GNU
// Lesser General Public License (LGPL) as published by the Free Software Foundation; either version
// 3 of the License, or (at your option) any later version. See <https://www.gnu.org/licenses/>.
use crate::Float;
use crate::InnerFloat::Finite;
use alloc::vec;
use core::cmp::Ordering::{self, *};
use malachite_base::num::arithmetic::traits::{DivisibleByPowerOf2, NegModPowerOf2, PowerOf2};
use malachite_base::num::basic::integers::PrimitiveInt;
use malachite_base::num::logic::traits::SignificantBits;
use malachite_base::rounding_modes::RoundingMode::{self, *};
use malachite_nz::natural::LIMB_HIGH_BIT;
use malachite_nz::natural::{Natural, bit_to_limb_count_ceiling};
use malachite_nz::platform::Limb;
impl Float {
/// Returns an approximation of a real number, given the number's bits. To avoid troublesome
/// edge cases, the number should not be a dyadic rational (and the iterator of bits should
/// therefore be infinite, and not eventually 0 or 1). Given this assumption, the rounding mode
/// `Exact` should never be passed.
///
/// The approximation has precision `prec` and is rounded according to the provided rounding
/// mode.
///
/// This function reads `prec + z` bits, or `prec + z + 1` bits if `rm` is `Nearest`, where `z`
/// is the number of leading false bits in `bits`.
///
/// This function always produces a value in the interval $[1/2,1]$. In particular, it never
/// overflows or underflows.
///
/// $$
/// f((x_k),p,m) = C+\varepsilon,
/// $$
/// where
/// $$
/// C=\sum_{k=0}^\infty x_k 2^{-(k+1)}.
/// $$
/// - If $m$ is not `Nearest`, then $|\varepsilon| < 2^{\lfloor\log_2 C\rfloor-p+1}$.
/// - If $m$ is `Nearest`, then $|\varepsilon| < 2^{\lfloor\log_2 C\rfloor-p}$.
///
/// The output has precision `prec`.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(n)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `prec`.
///
/// # Panics
/// Panics if `prec` is zero or `rm` is `Exact`.
///
/// # Examples
/// ```
/// use malachite_base::rounding_modes::RoundingMode::*;
/// use malachite_float::Float;
/// use std::cmp::Ordering::*;
///
/// // Produces 10100100010000100000...
/// struct Bits {
/// b: bool,
/// k: usize,
/// j: usize,
/// }
///
/// impl Iterator for Bits {
/// type Item = bool;
///
/// fn next(&mut self) -> Option<bool> {
/// Some(if self.b {
/// self.b = false;
/// self.j = self.k;
/// true
/// } else {
/// self.j -= 1;
/// if self.j == 0 {
/// self.k += 1;
/// self.b = true;
/// }
/// false
/// })
/// }
/// }
///
/// impl Bits {
/// fn new() -> Bits {
/// Bits {
/// b: true,
/// k: 1,
/// j: 1,
/// }
/// }
/// }
///
/// let (c, o) = Float::non_dyadic_from_bits_prec_round(Bits::new(), 100, Floor);
/// assert_eq!(c.to_string(), "0.6416325606551538662938427702254");
/// assert_eq!(o, Less);
///
/// let (c, o) = Float::non_dyadic_from_bits_prec_round(Bits::new(), 100, Ceiling);
/// assert_eq!(c.to_string(), "0.641632560655153866293842770226");
/// assert_eq!(o, Greater);
/// ```
pub fn non_dyadic_from_bits_prec_round<I: Iterator<Item = bool>>(
mut bits: I,
prec: u64,
rm: RoundingMode,
) -> (Self, Ordering) {
assert_ne!(prec, 0);
assert_ne!(rm, Exact);
let len = bit_to_limb_count_ceiling(prec);
let mut limbs = vec![0; len];
let mut limbs_it = limbs.iter_mut().rev();
let mut x = limbs_it.next().unwrap();
let mut mask = LIMB_HIGH_BIT;
let mut seen_one = false;
let mut exponent: i32 = 0;
let mut remaining = prec;
for b in &mut bits {
if !seen_one {
if b {
seen_one = true;
} else {
exponent = exponent.checked_sub(1).unwrap();
continue;
}
}
if b {
*x |= mask;
}
remaining -= 1;
if remaining == 0 {
break;
}
if mask == 1 {
x = limbs_it.next().unwrap();
mask = LIMB_HIGH_BIT;
} else {
mask >>= 1;
}
}
let mut significand = Natural::from_owned_limbs_asc(limbs);
let increment = rm == Up || rm == Ceiling || (rm == Nearest && bits.next() == Some(true));
if increment {
significand +=
Natural::from(Limb::power_of_2(prec.neg_mod_power_of_2(Limb::LOG_WIDTH)));
if !significand
.significant_bits()
.divisible_by_power_of_2(Limb::LOG_WIDTH)
{
significand >>= 1;
exponent += 1;
}
}
(
Self(Finite {
sign: true,
exponent,
precision: prec,
significand,
}),
if increment { Greater } else { Less },
)
}
/// Returns an approximation of a real number, given the number's bits. To avoid troublesome
/// edge cases, the number should not be a dyadic rational (and the iterator of bits should
/// therefore be infinite, and not eventually 0 or 1).
///
/// The approximation has precision `prec` and is rounded according to the `Nearest` rounding
/// mode.
///
/// This function reads `prec + z + 1` bits, where `z` is the number of leading false bits in
/// `bits`.
///
/// This function always produces a value in the interval $[1/2,1]$. In particular, it never
/// overflows or underflows.
///
/// $$
/// f((x_k),p,m) = C+\varepsilon,
/// $$
/// where
/// $$
/// C=\sum_{k=0}^\infty x_k 2^{-(k+1)}
/// $$
/// and $|\varepsilon| < 2^{\lfloor\log_2 C\rfloor-p}$.
///
/// The output has precision `prec`.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(n)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `prec`.
///
/// # Panics
/// Panics if `prec` is zero.
///
/// # Examples
/// ```
/// use malachite_float::Float;
/// use std::cmp::Ordering::*;
///
/// // Produces 10100100010000100000...
/// struct Bits {
/// b: bool,
/// k: usize,
/// j: usize,
/// }
///
/// impl Iterator for Bits {
/// type Item = bool;
///
/// fn next(&mut self) -> Option<bool> {
/// Some(if self.b {
/// self.b = false;
/// self.j = self.k;
/// true
/// } else {
/// self.j -= 1;
/// if self.j == 0 {
/// self.k += 1;
/// self.b = true;
/// }
/// false
/// })
/// }
/// }
///
/// impl Bits {
/// fn new() -> Bits {
/// Bits {
/// b: true,
/// k: 1,
/// j: 1,
/// }
/// }
/// }
///
/// let (c, o) = Float::non_dyadic_from_bits_prec(Bits::new(), 1);
/// assert_eq!(c.to_string(), "0.5");
/// assert_eq!(o, Less);
///
/// let (c, o) = Float::non_dyadic_from_bits_prec(Bits::new(), 10);
/// assert_eq!(c.to_string(), "0.642");
/// assert_eq!(o, Less);
///
/// let (c, o) = Float::non_dyadic_from_bits_prec(Bits::new(), 100);
/// assert_eq!(c.to_string(), "0.6416325606551538662938427702254");
/// assert_eq!(o, Less);
/// ```
#[inline]
pub fn non_dyadic_from_bits_prec<I: Iterator<Item = bool>>(
bits: I,
prec: u64,
) -> (Self, Ordering) {
Self::non_dyadic_from_bits_prec_round(bits, prec, Nearest)
}
}