code review 22730043: math/rand: Float32/64 must only return values in [0,1)

src/pkg/math/rand/rand.go

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // Package rand implements pseudo-random number generators.
 //
 // Random numbers are generated by a Source. Top-level functions, such as
 // Float64 and Int, use a default shared Source that produces a deterministic
 // sequence of values each time a program is run. Use the Seed function to
 // initialize the default Source if different behavior is required for each run.
@@ skipping 77 matching lines @@
         if n <= 0 {
                 panic("invalid argument to Intn")
         }
         if n <= 1<<31-1 {
                 return int(r.Int31n(int32(n)))
         }
         return int(r.Int63n(int64(n)))
 }
 
 // Float64 returns, as a float64, a pseudo-random number in [0.0,1.0).
-func (r *Rand) Float64() float64 { return float64(r.Int63()) / (1 << 63) }
+func (r *Rand) Float64() float64 { return float64(r.Int63n(1<<53)) / (1 << 53) }
 
 // Float32 returns, as a float32, a pseudo-random number in [0.0,1.0).
-func (r *Rand) Float32() float32 { return float32(r.Float64()) }
+func (r *Rand) Float32() float32 { return float32(r.Int31n(1<<24)) / (1 << 24) }
 
 // Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n).
 func (r *Rand) Perm(n int) []int {
         m := make([]int, n)
         for i := 0; i < n; i++ {
                 m[i] = i
         }
         for i := 0; i < n; i++ {
                 j := r.Intn(i + 1)
                 m[i], m[j] = m[j], m[i]
@@ skipping 85 matching lines @@
         n = r.src.Int63()
         r.lk.Unlock()
         return
 }
 
 func (r *lockedSource) Seed(seed int64) {
         r.lk.Lock()
         r.src.Seed(seed)
         r.lk.Unlock()
 }