src/distributions/integer.rs

// Copyright 2018 Developers of the Rand project.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! The implementations of the `Standard` distribution for integer types.

use crate::{Rng};
use crate::distributions::{Distribution, Standard};
use core::num::{NonZeroU8, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroUsize};
#[cfg(not(target_os = "emscripten"))] use core::num::NonZeroU128;
#[cfg(feature="simd_support")]
use packed_simd::*;
#[cfg(all(target_arch = "x86", feature="nightly"))]
use core::arch::x86::*;
#[cfg(all(target_arch = "x86_64", feature="nightly"))]
use core::arch::x86_64::*;

impl Distribution<u8> for Standard {
    #[inline]
    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> u8 {
        rng.next_u32() as u8
    }
}

impl Distribution<u16> for Standard {
    #[inline]
    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> u16 {
        rng.next_u32() as u16
    }
}

impl Distribution<u32> for Standard {
    #[inline]
    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> u32 {
        rng.next_u32()
    }
}

impl Distribution<u64> for Standard {
    #[inline]
    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> u64 {
        rng.next_u64()
    }
}

#[cfg(not(target_os = "emscripten"))]
impl Distribution<u128> for Standard {
    #[inline]
    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> u128 {
        // Use LE; we explicitly generate one value before the next.
        let x = u128::from(rng.next_u64());
        let y = u128::from(rng.next_u64());
        (y << 64) | x
    }
}

impl Distribution<usize> for Standard {
    #[inline]
    #[cfg(any(target_pointer_width = "32", target_pointer_width = "16"))]
    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> usize {
        rng.next_u32() as usize
    }

    #[inline]
    #[cfg(target_pointer_width = "64")]
    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> usize {
        rng.next_u64() as usize
    }
}

macro_rules! impl_int_from_uint {
    ($ty:ty, $uty:ty) => {
        impl Distribution<$ty> for Standard {
            #[inline]
            fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> $ty {
                rng.gen::<$uty>() as $ty
            }
        }
    }
}

impl_int_from_uint! { i8, u8 }
impl_int_from_uint! { i16, u16 }
impl_int_from_uint! { i32, u32 }
impl_int_from_uint! { i64, u64 }
#[cfg(not(target_os = "emscripten"))] impl_int_from_uint! { i128, u128 }
impl_int_from_uint! { isize, usize }

macro_rules! impl_nzint {
    ($ty:ty, $new:path) => {
        impl Distribution<$ty> for Standard {
            fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> $ty {
                loop {
                    if let Some(nz) = $new(rng.gen()) {
                        break nz;
                    }
                }
            }
        }
    }
}

impl_nzint!(NonZeroU8, NonZeroU8::new);
impl_nzint!(NonZeroU16, NonZeroU16::new);
impl_nzint!(NonZeroU32, NonZeroU32::new);
impl_nzint!(NonZeroU64, NonZeroU64::new);
#[cfg(not(target_os = "emscripten"))] impl_nzint!(NonZeroU128, NonZeroU128::new);
impl_nzint!(NonZeroUsize, NonZeroUsize::new);

#[cfg(feature="simd_support")]
macro_rules! simd_impl {
    ($(($intrinsic:ident, $vec:ty),)+) => {$(
        impl Distribution<$intrinsic> for Standard {
            #[inline]
            fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> $intrinsic {
                $intrinsic::from_bits(rng.gen::<$vec>())
            }
        }
    )+};

    ($bits:expr,) => {};
    ($bits:expr, $ty:ty, $($ty_more:ty,)*) => {
        simd_impl!($bits, $($ty_more,)*);

        impl Distribution<$ty> for Standard {
            #[inline]
            fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> $ty {
                let mut vec: $ty = Default::default();
                unsafe {
                    let ptr = &mut vec;
                    let b_ptr = &mut *(ptr as *mut $ty as *mut [u8; $bits/8]);
                    rng.fill_bytes(b_ptr);
                }
                vec.to_le()
            }
        }
    };
}

#[cfg(feature="simd_support")]
simd_impl!(16, u8x2, i8x2,);
#[cfg(feature="simd_support")]
simd_impl!(32, u8x4, i8x4, u16x2, i16x2,);
#[cfg(feature="simd_support")]
simd_impl!(64, u8x8, i8x8, u16x4, i16x4, u32x2, i32x2,);
#[cfg(feature="simd_support")]
simd_impl!(128, u8x16, i8x16, u16x8, i16x8, u32x4, i32x4, u64x2, i64x2,);
#[cfg(feature="simd_support")]
simd_impl!(256, u8x32, i8x32, u16x16, i16x16, u32x8, i32x8, u64x4, i64x4,);
#[cfg(feature="simd_support")]
simd_impl!(512, u8x64, i8x64, u16x32, i16x32, u32x16, i32x16, u64x8, i64x8,);
#[cfg(all(feature="simd_support", feature="nightly", any(target_arch="x86", target_arch="x86_64")))]
simd_impl!((__m64, u8x8), (__m128i, u8x16), (__m256i, u8x32),);

#[cfg(test)]
mod tests {
    use super::*;
    
    #[test]
    fn test_integers() {
        let mut rng = crate::test::rng(806);
        
        rng.sample::<isize, _>(Standard);
        rng.sample::<i8, _>(Standard);
        rng.sample::<i16, _>(Standard);
        rng.sample::<i32, _>(Standard);
        rng.sample::<i64, _>(Standard);
        #[cfg(not(target_os = "emscripten"))]
        rng.sample::<i128, _>(Standard);
        
        rng.sample::<usize, _>(Standard);
        rng.sample::<u8, _>(Standard);
        rng.sample::<u16, _>(Standard);
        rng.sample::<u32, _>(Standard);
        rng.sample::<u64, _>(Standard);
        #[cfg(not(target_os = "emscripten"))]
        rng.sample::<u128, _>(Standard);
    }
    
    #[test]
    fn value_stability() {
        fn test_samples<T: Copy + core::fmt::Debug + PartialEq>(
            zero: T, expected: &[T]
        )
        where Standard: Distribution<T>
        {
            let mut rng = crate::test::rng(807);
            let mut buf = [zero; 3];
            for x in &mut buf {
                *x = rng.sample(Standard);
            }
            assert_eq!(&buf, expected);
        }
        
        test_samples(0u8, &[9, 247, 111]);
        test_samples(0u16, &[32265, 42999, 38255]);
        test_samples(0u32, &[2220326409, 2575017975, 2018088303]);
        test_samples(0u64, &[11059617991457472009,
                16096616328739788143, 1487364411147516184]);
        test_samples(0u128, &[296930161868957086625409848350820761097,
                145644820879247630242265036535529306392,
                111087889832015897993126088499035356354]);
        #[cfg(any(target_pointer_width = "32", target_pointer_width = "16"))]
        test_samples(0usize, &[2220326409, 2575017975, 2018088303]);
        #[cfg(target_pointer_width = "64")]
        test_samples(0usize, &[11059617991457472009,
                16096616328739788143, 1487364411147516184]);
        
        test_samples(0i8, &[9, -9, 111]);
        // Skip further i* types: they are simple reinterpretation of u* samples
        
        #[cfg(feature="simd_support")] {
            // We only test a sub-set of types here and make assumptions about the rest.
            
            test_samples(u8x2::default(), &[u8x2::new(9, 126),
                    u8x2::new(247, 167), u8x2::new(111, 149)]);
            test_samples(u8x4::default(), &[u8x4::new(9, 126, 87, 132),
                    u8x4::new(247, 167, 123, 153), u8x4::new(111, 149, 73, 120)]);
            test_samples(u8x8::default(), &[
                    u8x8::new(9, 126, 87, 132, 247, 167, 123, 153),
                    u8x8::new(111, 149, 73, 120, 68, 171, 98, 223),
                    u8x8::new(24, 121, 1, 50, 13, 46, 164, 20)]);
            
            test_samples(i64x8::default(), &[
                    i64x8::new(-7387126082252079607, -2350127744969763473,
                        1487364411147516184, 7895421560427121838,
                        602190064936008898, 6022086574635100741,
                        -5080089175222015595, -4066367846667249123),
                    i64x8::new(9180885022207963908, 3095981199532211089,
                        6586075293021332726, 419343203796414657,
                        3186951873057035255, 5287129228749947252,
                        444726432079249540, -1587028029513790706),
                    i64x8::new(6075236523189346388, 1351763722368165432,
                        -6192309979959753740, -7697775502176768592,
                        -4482022114172078123, 7522501477800909500,
                        -1837258847956201231, -586926753024886735)]);
        }
    }
}