From db34b5acd150d114f392c907fa28f92a5227d3db Mon Sep 17 00:00:00 2001 From: Jed Davis Date: Mon, 16 Jul 2012 19:28:32 -0700 Subject: [PATCH] Prevent random floats from occasionally being greater than 1. Previously, gen_f64 could generate numbers as high as 1.0000000002328306 in the case that u3 was 4294967295.0f64 and u2 was nonzero. This change divides the random numbers by 2**32 instead, effectively concatenating their bits as apparently intended. (Bonus fix: const.) The comments are updated to be more specific than "random float"; note that this can still generate 1.0f64 (P = 2**-54) due to rounding. --- src/libcore/rand.rs | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/src/libcore/rand.rs b/src/libcore/rand.rs index 8d392e1be90f..16979f7ad95c 100644 --- a/src/libcore/rand.rs +++ b/src/libcore/rand.rs @@ -94,22 +94,22 @@ impl extensions for rng { (self.next() as u64 << 32) | self.next() as u64 } - /// Return a random float + /// Return a random float in the interval [0,1] fn gen_float() -> float { self.gen_f64() as float } - /// Return a random f32 + /// Return a random f32 in the interval [0,1] fn gen_f32() -> f32 { self.gen_f64() as f32 } - /// Return a random f64 + /// Return a random f64 in the interval [0,1] fn gen_f64() -> f64 { let u1 = self.next() as f64; let u2 = self.next() as f64; let u3 = self.next() as f64; - let scale = u32::max_value as f64; + const scale : f64 = (u32::max_value as f64) + 1.0f64; ret ((u1 / scale + u2) / scale + u3) / scale; }