Make const
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@ -2,7 +2,7 @@
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name = "integer-sqrt"
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description = """
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An implementation of integer square root algorithm for primitive rust types"""
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version = "0.1.5"
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version = "0.2.0"
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authors = ["Richard Dodd <richard.o.dodd@gmail.com>", "Joseph Richey", "Sergei Shulepov"]
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include = ["src/**/*.rs", "Cargo.toml"]
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repository = "https://github.com/derekdreery/integer-sqrt-rs"
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@ -10,6 +10,7 @@ readme = "README.md"
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keywords = ["integer", "square", "root", "isqrt", "sqrt"]
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categories = ["algorithms", "no-std"]
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license = "Apache-2.0/MIT"
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edition = "2021"
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[dependencies]
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num-traits = { version = "0.2", default-features = false }
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static_assertions = "1.1"
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55
src/lib.rs
55
src/lib.rs
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@ -16,6 +16,9 @@
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//!
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//! [`IntegerSquareRoot`]: ./trait.IntegerSquareRoot.html
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#![no_std]
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#![feature(const_trait_impl)]
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#![feature(const_fn_trait_bound)]
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#![feature(const_option)]
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/// A trait implementing integer square root.
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pub trait IntegerSquareRoot {
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@ -29,6 +32,7 @@ pub trait IntegerSquareRoot {
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/// For negative numbers (`i` family) this function will panic on negative input
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///
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/// [wiki_article]: https://en.wikipedia.org/wiki/Integer_square_root
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#[default_method_body_is_const]
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fn integer_sqrt(&self) -> Self
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where
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Self: Sized,
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@ -44,39 +48,62 @@ pub trait IntegerSquareRoot {
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Self: Sized;
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}
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impl<T: num_traits::PrimInt> IntegerSquareRoot for T {
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fn integer_sqrt_checked(&self) -> Option<Self> {
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macro_rules! integer_sqrt {
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($ty:ty as $unsigned_ty:ty, $value:expr) => {{
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static_assertions::assert_eq_size!($ty, $unsigned_ty);
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use core::cmp::Ordering;
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match self.cmp(&T::zero()) {
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match $value {
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0 => return Some(0),
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// Hopefully this will be stripped for unsigned numbers (impossible condition)
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Ordering::Less => return None,
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Ordering::Equal => return Some(T::zero()),
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v if v < 0 => return None,
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_ => {}
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}
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// Compute bit, the largest power of 4 <= n
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let max_shift: u32 = T::zero().leading_zeros() - 1;
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let shift: u32 = (max_shift - self.leading_zeros()) & !1;
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let mut bit = T::one().unsigned_shl(shift);
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const ZERO: $ty = 0;
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let max_shift: u32 = ZERO.leading_zeros() - 1;
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let shift: u32 = (max_shift - $value.leading_zeros()) & !1;
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let mut bit = (1 as $unsigned_ty << shift) as $ty;
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// Algorithm based on the implementation in:
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// https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Binary_numeral_system_(base_2)
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// Note that result/bit are logically unsigned (even if T is signed).
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let mut n = *self;
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let mut result = T::zero();
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while bit != T::zero() {
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let mut n = $value;
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let mut result = 0;
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while bit != 0 {
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if n >= (result + bit) {
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n = n - (result + bit);
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result = result.unsigned_shr(1) + bit;
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result = (result as $unsigned_ty >> 1) as $ty + bit;
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} else {
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result = result.unsigned_shr(1);
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result = (result as $unsigned_ty >> 1) as $ty;
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}
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bit = bit.unsigned_shr(2);
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bit = (bit as $unsigned_ty >> 2) as $ty;
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}
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Some(result)
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}};
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(impl const $ty:ty as $unsigned_ty:ty) => {
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impl const IntegerSquareRoot for $ty {
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fn integer_sqrt_checked(&self) -> Option<Self> {
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integer_sqrt!($ty as $unsigned_ty, *self)
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}
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}
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};
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}
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integer_sqrt!(impl const u8 as u8);
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integer_sqrt!(impl const u16 as u16);
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integer_sqrt!(impl const u32 as u32);
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integer_sqrt!(impl const u64 as u64);
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integer_sqrt!(impl const u128 as u128);
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integer_sqrt!(impl const usize as usize);
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integer_sqrt!(impl const i8 as u8);
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integer_sqrt!(impl const i16 as u16);
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integer_sqrt!(impl const i32 as u32);
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integer_sqrt!(impl const i64 as u64);
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integer_sqrt!(impl const i128 as u128);
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integer_sqrt!(impl const isize as usize);
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#[cfg(test)]
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mod tests {
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use super::IntegerSquareRoot;
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