src/librand/rand_impls.rs

   1 // Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! The implementations of `Rand` for the built-in types.
  12
  13 use core::prelude::*;
  14 use core::char;
  15 use core::int;
  16 use core::uint;
  17
  18 use {Rand,Rng};
  19
  20 impl Rand for int {
  21     #[inline]
  22     fn rand<R: Rng>(rng: &mut R) -> int {
  23         if int::BITS == 32 {
  24             rng.gen::<i32>() as int
  25         } else {
  26             rng.gen::<i64>() as int
  27         }
  28     }
  29 }
  30
  31 impl Rand for i8 {
  32     #[inline]
  33     fn rand<R: Rng>(rng: &mut R) -> i8 {
  34         rng.next_u32() as i8
  35     }
  36 }
  37
  38 impl Rand for i16 {
  39     #[inline]
  40     fn rand<R: Rng>(rng: &mut R) -> i16 {
  41         rng.next_u32() as i16
  42     }
  43 }
  44
  45 impl Rand for i32 {
  46     #[inline]
  47     fn rand<R: Rng>(rng: &mut R) -> i32 {
  48         rng.next_u32() as i32
  49     }
  50 }
  51
  52 impl Rand for i64 {
  53     #[inline]
  54     fn rand<R: Rng>(rng: &mut R) -> i64 {
  55         rng.next_u64() as i64
  56     }
  57 }
  58
  59 impl Rand for uint {
  60     #[inline]
  61     fn rand<R: Rng>(rng: &mut R) -> uint {
  62         if uint::BITS == 32 {
  63             rng.gen::<u32>() as uint
  64         } else {
  65             rng.gen::<u64>() as uint
  66         }
  67     }
  68 }
  69
  70 impl Rand for u8 {
  71     #[inline]
  72     fn rand<R: Rng>(rng: &mut R) -> u8 {
  73         rng.next_u32() as u8
  74     }
  75 }
  76
  77 impl Rand for u16 {
  78     #[inline]
  79     fn rand<R: Rng>(rng: &mut R) -> u16 {
  80         rng.next_u32() as u16
  81     }
  82 }
  83
  84 impl Rand for u32 {
  85     #[inline]
  86     fn rand<R: Rng>(rng: &mut R) -> u32 {
  87         rng.next_u32()
  88     }
  89 }
  90
  91 impl Rand for u64 {
  92     #[inline]
  93     fn rand<R: Rng>(rng: &mut R) -> u64 {
  94         rng.next_u64()
  95     }
  96 }
  97
  98 macro_rules! float_impls {
  99     ($mod_name:ident, $ty:ty, $mantissa_bits:expr, $method_name:ident) => {
 100         mod $mod_name {
 101             use {Rand, Rng, Open01, Closed01};
 102
 103             const SCALE: $ty = (1u64 << $mantissa_bits) as $ty;
 104
 105             impl Rand for $ty {
 106                 /// Generate a floating point number in the half-open
 107                 /// interval `[0,1)`.
 108                 ///
 109                 /// See `Closed01` for the closed interval `[0,1]`,
 110                 /// and `Open01` for the open interval `(0,1)`.
 111                 #[inline]
 112                 fn rand<R: Rng>(rng: &mut R) -> $ty {
 113                     rng.$method_name()
 114                 }
 115             }
 116             impl Rand for Open01<$ty> {
 117                 #[inline]
 118                 fn rand<R: Rng>(rng: &mut R) -> Open01<$ty> {
 119                     // add a small amount (specifically 2 bits below
 120                     // the precision of f64/f32 at 1.0), so that small
 121                     // numbers are larger than 0, but large numbers
 122                     // aren't pushed to/above 1.
 123                     Open01(rng.$method_name() + 0.25 / SCALE)
 124                 }
 125             }
 126             impl Rand for Closed01<$ty> {
 127                 #[inline]
 128                 fn rand<R: Rng>(rng: &mut R) -> Closed01<$ty> {
 129                     // rescale so that 1.0 - epsilon becomes 1.0
 130                     // precisely.
 131                     Closed01(rng.$method_name() * SCALE / (SCALE - 1.0))
 132                 }
 133             }
 134         }
 135     }
 136 }
 137 float_impls! { f64_rand_impls, f64, 53, next_f64 }
 138 float_impls! { f32_rand_impls, f32, 24, next_f32 }
 139
 140 impl Rand for char {
 141     #[inline]
 142     fn rand<R: Rng>(rng: &mut R) -> char {
 143         // a char is 21 bits
 144         static CHAR_MASK: u32 = 0x001f_ffff;
 145         loop {
 146             // Rejection sampling. About 0.2% of numbers with at most
 147             // 21-bits are invalid codepoints (surrogates), so this
 148             // will succeed first go almost every time.
 149             match char::from_u32(rng.next_u32() & CHAR_MASK) {
 150                 Some(c) => return c,
 151                 None => {}
 152             }
 153         }
 154     }
 155 }
 156
 157 impl Rand for bool {
 158     #[inline]
 159     fn rand<R: Rng>(rng: &mut R) -> bool {
 160         rng.gen::<u8>() & 1 == 1
 161     }
 162 }
 163
 164 macro_rules! tuple_impl {
 165     // use variables to indicate the arity of the tuple
 166     ($($tyvar:ident),* ) => {
 167         // the trailing commas are for the 1 tuple
 168         impl<
 169             $( $tyvar : Rand ),*
 170             > Rand for ( $( $tyvar ),* , ) {
 171
 172             #[inline]
 173             fn rand<R: Rng>(_rng: &mut R) -> ( $( $tyvar ),* , ) {
 174                 (
 175                     // use the $tyvar's to get the appropriate number of
 176                     // repeats (they're not actually needed)
 177                     $(
 178                         _rng.gen::<$tyvar>()
 179                     ),*
 180                     ,
 181                 )
 182             }
 183         }
 184     }
 185 }
 186
 187 impl Rand for () {
 188     #[inline]
 189     fn rand<R: Rng>(_: &mut R) -> () { () }
 190 }
 191 tuple_impl!{A}
 192 tuple_impl!{A, B}
 193 tuple_impl!{A, B, C}
 194 tuple_impl!{A, B, C, D}
 195 tuple_impl!{A, B, C, D, E}
 196 tuple_impl!{A, B, C, D, E, F}
 197 tuple_impl!{A, B, C, D, E, F, G}
 198 tuple_impl!{A, B, C, D, E, F, G, H}
 199 tuple_impl!{A, B, C, D, E, F, G, H, I}
 200 tuple_impl!{A, B, C, D, E, F, G, H, I, J}
 201 tuple_impl!{A, B, C, D, E, F, G, H, I, J, K}
 202 tuple_impl!{A, B, C, D, E, F, G, H, I, J, K, L}
 203
 204 impl<T:Rand> Rand for Option<T> {
 205     #[inline]
 206     fn rand<R: Rng>(rng: &mut R) -> Option<T> {
 207         if rng.gen() {
 208             Some(rng.gen())
 209         } else {
 210             None
 211         }
 212     }
 213 }
 214
 215 #[cfg(test)]
 216 mod tests {
 217     use std::prelude::v1::*;
 218     use std::rand::{Rng, thread_rng, Open01, Closed01};
 219
 220     struct ConstantRng(u64);
 221     impl Rng for ConstantRng {
 222         fn next_u32(&mut self) -> u32 {
 223             let ConstantRng(v) = *self;
 224             v as u32
 225         }
 226         fn next_u64(&mut self) -> u64 {
 227             let ConstantRng(v) = *self;
 228             v
 229         }
 230     }
 231
 232     #[test]
 233     fn floating_point_edge_cases() {
 234         // the test for exact equality is correct here.
 235         assert!(ConstantRng(0xffff_ffff).gen::<f32>() != 1.0);
 236         assert!(ConstantRng(0xffff_ffff_ffff_ffff).gen::<f64>() != 1.0);
 237     }
 238
 239     #[test]
 240     fn rand_open() {
 241         // this is unlikely to catch an incorrect implementation that
 242         // generates exactly 0 or 1, but it keeps it sane.
 243         let mut rng = thread_rng();
 244         for _ in range(0u, 1_000) {
 245             // strict inequalities
 246             let Open01(f) = rng.gen::<Open01<f64>>();
 247             assert!(0.0 < f && f < 1.0);
 248
 249             let Open01(f) = rng.gen::<Open01<f32>>();
 250             assert!(0.0 < f && f < 1.0);
 251         }
 252     }
 253
 254     #[test]
 255     fn rand_closed() {
 256         let mut rng = thread_rng();
 257         for _ in range(0u, 1_000) {
 258             // strict inequalities
 259             let Closed01(f) = rng.gen::<Closed01<f64>>();
 260             assert!(0.0 <= f && f <= 1.0);
 261
 262             let Closed01(f) = rng.gen::<Closed01<f32>>();
 263             assert!(0.0 <= f && f <= 1.0);
 264         }
 265     }
 266 }