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std::rand: adjust the f32 & f64 Rand instances.

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The f32 generator now just uses a single u32, and the f64 uses a
single u64. This will make both significantly faster, especially
on 64-bit platforms.
This commit is contained in:
Huon Wilson 2013-10-03 13:10:34 +10:00
parent 98869799eb
commit 9db32a2f1d
1 changed files with 8 additions and 7 deletions
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15
src/libstd/rand/rand_impls.rs
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@ -14,7 +14,6 @@ use char;
use int;
use option::{Option, Some, None};
use rand::{Rand,Rng};
use u32;
use uint;
impl Rand for int {
@ -96,21 +95,23 @@ impl Rand for u64 {
}
impl Rand for f32 {
/// A random `f32` in the range `[0, 1)`.
#[inline]
fn rand<R: Rng>(rng: &mut R) -> f32 {
rng.gen::<f64>() as f32
// weird, but this is the easiest way to get 2**32
static SCALE: f32 = 2.0 * (1u32 << 31) as f32;
rng.next_u32() as f32 / SCALE
}
}
static SCALE : f64 = (u32::max_value as f64) + 1.0f64;
impl Rand for f64 {
/// A random `f64` in the range `[0, 1)`.
#[inline]
fn rand<R: Rng>(rng: &mut R) -> f64 {
let u1 = rng.next_u32() as f64;
let u2 = rng.next_u32() as f64;
let u3 = rng.next_u32() as f64;
// weird, but this is the easiest way to get 2**64
static SCALE: f64 = 2.0 * (1u64 << 63) as f64;
((u1 / SCALE + u2) / SCALE + u3) / SCALE
rng.next_u64() as f64 / SCALE
}
}