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/*
Copyright 2024-2025 Owain Davies
SPDX-License-Identifier: Apache-2.0 OR MIT
*/
use crate::{Arbi, BitCount};
impl Arbi {
/// Returns the base-`base` logarithm of the number, rounded down.
///
/// # Panics
/// This function will panic if `self` is less than or equal to zero, or if
/// `base` is less than 2.
///
/// # Examples
/// ```
/// use arbi::Arbi;
/// let a = Arbi::from(10);
/// assert_eq!(a.ilog(8), 1);
/// ```
///
/// Nonpositive values panic:
/// ```should_panic
/// use arbi::Arbi;
/// let zero = Arbi::zero();
/// zero.ilog(8);
/// ```
///
/// ```should_panic
/// use arbi::Arbi;
/// let minus_one = Arbi::neg_one();
/// minus_one.ilog(8);
/// ```
///
/// A base less than 2 causes a panic
/// ```should_panic
/// use arbi::Arbi;
/// let a = Arbi::from(4);
/// a.ilog(1);
/// ```
pub fn ilog(self, base: u32) -> BitCount {
Self::check_ilog_args(&self, base);
self.size_base(base) - 1
}
/// Returns the base-`base` logarithm of the number, rounded down.
///
/// # Panics
/// This function will panic if `self` is less than or equal to zero, or if
/// `base` is less than 2.
///
/// # Examples
/// ```
/// use arbi::Arbi;
/// let mut a = Arbi::from(10);
/// a.ilog_mut(8);
/// assert_eq!(a, 1);
/// ```
///
/// Nonpositive values panic:
/// ```should_panic
/// use arbi::Arbi;
/// let mut zero = Arbi::zero();
/// zero.ilog_mut(8);
/// ```
/// ```should_panic
/// use arbi::Arbi;
/// let mut minus_one = Arbi::neg_one();
/// minus_one.ilog_mut(8);
/// ```
///
/// A base less than 2 causes a panic
/// ```should_panic
/// use arbi::Arbi;
/// let mut a = Arbi::from(4);
/// a.ilog_mut(1);
/// ```
pub fn ilog_mut(&mut self, base: u32) -> BitCount {
Self::check_ilog_args(self, base);
let ret = self.size_base_mut(base) - 1;
*self -= 1;
ret
}
/// Returns the base-`base` logarithm of the number, rounded down.
///
/// # Panics
/// This function will panic if `self` is less than or equal to zero, or if
/// `base` is less than 2.
///
/// # Examples
/// ```
/// use arbi::Arbi;
/// let a = Arbi::from(10);
/// assert_eq!(a.ilog_ref(8), 1);
/// ```
///
/// Nonpositive values panic:
/// ```should_panic
/// use arbi::Arbi;
/// let zero = Arbi::zero();
/// zero.ilog_ref(8);
/// ```
/// ```should_panic
/// use arbi::Arbi;
/// let minus_one = Arbi::neg_one();
/// minus_one.ilog_ref(8);
/// ```
///
/// A base less than 2 causes a panic
/// ```should_panic
/// use arbi::Arbi;
/// let a = Arbi::from(4);
/// a.ilog_ref(1);
/// ```
pub fn ilog_ref(&self, base: u32) -> BitCount {
Self::check_ilog_args(self, base);
self.size_base_ref(base) - 1
}
fn check_ilog_args(x: &Self, base: u32) {
if x <= 0 {
panic!("self must be positive: {x}");
}
if base < 2 {
panic!("base must be greater than or equal to 2: {base}");
}
}
}
#[cfg(test)]
mod tests {
use crate::uints::UnsignedUtilities;
use crate::util::test::{get_seedable_rng, get_uniform_die, Distribution};
use crate::{Arbi, BitCount, DDigit, Digit, QDigit};
#[test]
fn test_digit_boundaries() {
for base in 2u32..=36u32 {
let a = Arbi::from(Digit::MAX);
assert_eq!(
a.ilog_ref(base),
Digit::ilog_(Digit::MAX, base) as BitCount
);
let a = Arbi::from(Digit::MAX as DDigit + 1);
assert_eq!(
a.ilog_ref(base),
DDigit::ilog_(Digit::MAX as DDigit + 1, base as DDigit)
as BitCount
);
let a = Arbi::from(DDigit::MAX);
assert_eq!(
a.ilog_ref(base),
DDigit::ilog_(DDigit::MAX, base as DDigit) as BitCount
);
let a = Arbi::from(DDigit::MAX as QDigit + 1);
assert_eq!(
a.ilog_ref(base),
QDigit::ilog_(DDigit::MAX as QDigit + 1, base as QDigit)
as BitCount
);
}
}
#[test]
#[should_panic = "self must be positive: 0"]
fn test_zero() {
let a = Arbi::zero();
a.ilog_ref(8);
}
#[test]
#[should_panic = "self must be positive: -4"]
fn test_is_power_of_two_negative() {
let a = Arbi::from(-4);
a.ilog_ref(8);
}
#[test]
#[should_panic = "base must be greater than or equal to 2: 0"]
fn test_invalid_base() {
let a = Arbi::from(4);
a.ilog_ref(0);
}
#[test]
fn smoke() {
let (mut rng, _) = get_seedable_rng();
let die_digit = get_uniform_die(Digit::MIN, Digit::MAX);
let die_ddigit = get_uniform_die(Digit::MAX as DDigit + 1, DDigit::MAX);
let die_qdigit =
get_uniform_die(DDigit::MAX as QDigit + 1, QDigit::MAX);
for base in 2u32..=36u32 {
for _ in 0..i16::MAX {
let r = die_digit.sample(&mut rng);
if r == 0 {
continue;
}
let a = Arbi::from(r);
assert_eq!(a.ilog_ref(base), Digit::ilog_(r, base) as BitCount);
let r = die_ddigit.sample(&mut rng);
let a = Arbi::from(r);
assert_eq!(
a.ilog_ref(base),
DDigit::ilog_(r, base as DDigit) as BitCount
);
let r = die_qdigit.sample(&mut rng);
let a = Arbi::from(r);
assert_eq!(
a.ilog_ref(base),
QDigit::ilog_(r, base as QDigit) as BitCount
);
}
}
}
}