diff options
author | Russ Cox <rsc@golang.org> | 2009-12-15 17:21:34 -0800 |
---|---|---|
committer | Russ Cox <rsc@golang.org> | 2009-12-15 17:21:34 -0800 |
commit | f64bb56bae3029ab2491bd40634284677ab191e5 (patch) | |
tree | f846db7bcaeab16efd356a2ffca01173071f2521 | |
parent | 1e9e7ec4b3e4c7bb9b014398ea07b7c3f3ae0f21 (diff) | |
download | go-f64bb56bae3029ab2491bd40634284677ab191e5.tar.gz go-f64bb56bae3029ab2491bd40634284677ab191e5.zip |
rand: add explicit Int31n to avoid 64-bit divide on 32-bit machines
use Int31n in Intn when possible.
Fixes #390.
(using 8g)
Intn1000 50000000 38 ns/op
Int31n1000 50000000 39 ns/op
Int63n1000 20000000 114 ns/op
R=r
CC=golang-dev, skybrian
https://golang.org/cl/180054
-rw-r--r-- | src/pkg/rand/rand.go | 19 | ||||
-rw-r--r-- | src/pkg/rand/rand_test.go | 21 |
2 files changed, 38 insertions, 2 deletions
diff --git a/src/pkg/rand/rand.go b/src/pkg/rand/rand.go index 0d7eaa79a1..8c1219a7a1 100644 --- a/src/pkg/rand/rand.go +++ b/src/pkg/rand/rand.go @@ -62,10 +62,25 @@ func (r *Rand) Int63n(n int64) int64 { } // Int31n returns, as an int32, a non-negative pseudo-random number in [0,n). -func (r *Rand) Int31n(n int32) int32 { return int32(r.Int63n(int64(n))) } +func (r *Rand) Int31n(n int32) int32 { + if n <= 0 { + return 0 + } + max := int32((1 << 31) - 1 - (1<<31)%uint32(n)) + v := r.Int31() + for v > max { + v = r.Int31() + } + return v % n +} // Intn returns, as an int, a non-negative pseudo-random number in [0,n). -func (r *Rand) Intn(n int) int { return int(r.Int63n(int64(n))) } +func (r *Rand) Intn(n int) int { + 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) } diff --git a/src/pkg/rand/rand_test.go b/src/pkg/rand/rand_test.go index b90c69db7f..786831517d 100644 --- a/src/pkg/rand/rand_test.go +++ b/src/pkg/rand/rand_test.go @@ -327,3 +327,24 @@ func BenchmarkInt63Unthreadsafe(b *testing.B) { r.Int63() } } + +func BenchmarkIntn1000(b *testing.B) { + r := New(NewSource(1)) + for n := b.N; n > 0; n-- { + r.Intn(1000) + } +} + +func BenchmarkInt63n1000(b *testing.B) { + r := New(NewSource(1)) + for n := b.N; n > 0; n-- { + r.Int63n(1000) + } +} + +func BenchmarkInt31n1000(b *testing.B) { + r := New(NewSource(1)) + for n := b.N; n > 0; n-- { + r.Int31n(1000) + } +} |