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document rand

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R=rsc
DELTA=27  (16 added, 8 deleted, 3 changed)
OCL=25804
CL=25813
This commit is contained in:
Rob Pike 2009-03-05 19:26:27 -08:00
parent 37656ad568
commit 6b8ac0a9e4
1 changed files with 18 additions and 11 deletions
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29
src/lib/rand.go
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@ -2,24 +2,19 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Uniformly distributed pseudo-random numbers.
package rand
/*
* algorithm by
* DP Mitchell and JA Reeds
*/
package rand
// rand, rand31, Int63 - return non-negative random int, int32, int64
// urand32 - return random uint32
// nrand, nrand31, Int63n - return 0 <= random < n
// frand, frand64, frand32 - return 0 <= random float, float64, float32 < 1
// perm gives a random permutation []int
const (
_LEN = 607;
_TAP = 273;
_MASK = (1<<63)-1;
_MAX = 1<<63;
_MASK = _MAX-1;
_A = 48271;
_M = 2147483647;
_Q = 44488;
@ -44,6 +39,7 @@ func seedrand(x int32) int32 {
return x;
}
// Seed uses the provided seed value to initialize the generator to a deterministic state.
func Seed(seed int32) {
rng_tap = 0;
rng_feed = _LEN-_TAP;
@ -72,6 +68,7 @@ func Seed(seed int32) {
}
}
// Int63 returns a non-negative pseudo-random 63-bit integer as an int64.
func Int63() int64 {
rng_tap--;
if rng_tap < 0 {
@ -88,19 +85,23 @@ func Int63() int64 {
return x;
}
// Uint32 returns a pseudo-random 32-bit value as a uint32.
func Uint32() uint32 {
return uint32(Int63() >> 31);
}
// Int31 returns a non-negative pseudo-random 31-bit integer as an int32.
func Int31() int32 {
return int32(Int63() >> 32);
}
// Int returns a non-negative pseudo-random int. All bits but the top bit are random.
func Int() int {
u := uint(Int63());
return int(u << 1 >> 1); // clear sign bit if int == int32
}
// Int63n returns, as an int64, a non-negative pseudo-random number in [0,n).
func Int63n(n int64) int64 {
if n <= 0 {
return 0
@ -113,31 +114,37 @@ func Int63n(n int64) int64 {
return v % n
}
// Int31n returns, as an int32, a non-negative pseudo-random number in [0,n).
func Int31n(n int32) int32 {
return int32(Int63n(int64(n)))
}
// Intn returns, as an int, a non-negative pseudo-random number in [0,n).
func Intn(n int) int {
return int(Int63n(int64(n)))
}
// Float64 returns, as a float64, a pseudo-random number in [0.0,1.0).
func Float64() float64 {
x := float64(Int63()) / float64(_MASK);
x := float64(Int63()) / float64(_MAX);
for x >= 1 {
x = float64(Int63()) / float64(_MASK);
x = float64(Int63()) / float64(_MAX);
}
return x;
}
// Float32 returns, as a float32, a pseudo-random number in [0.0,1.0).
func Float32() float32 {
return float32(Float64())
}
// Float returns, as a float, a pseudo-random number in [0.0,1.0).
func Float() float
{
return float(Float64())
}
// Perm returns, as an array of n ints, a pseudo-random permutation of the integers [0,n).
func Perm(n int) []int {
m := make([]int, n);
for i:=0; i<n; i++ {