math/rand: refactor rng.go

Made constant names more idiomatic,
moved some constants to function seedrand,
and found better name for _M.

Change-Id: I192172f398378bef486a5bbceb6ba86af48ebcc9
Reviewed-on: https://go-review.googlesource.com/107135
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/math/rand/rng.go b/src/math/rand/rng.go
index f922417cdc4eaba5359fb254799fb1e26f8b608e..f305df1a20b857e06a4b79f15b9e00fe65cbb1f9 100644 (file)
--- a/src/math/rand/rng.go
+++ b/src/math/rand/rng.go
@@ -12,19 +12,16 @@ package rand
  */
 
 const (
-       _LEN  = 607
-       _TAP  = 273
-       _MAX  = 1 << 63
-       _MASK = _MAX - 1
-       _A    = 48271
-       _M    = (1 << 31) - 1
-       _Q    = 44488
-       _R    = 3399
+       rngLen   = 607
+       rngTap   = 273
+       rngMax   = 1 << 63
+       rngMask  = rngMax - 1
+       int32max = (1 << 31) - 1
 )
 
 var (
-       // Used for seeding. See gen_cooked.go for details.
-       rng_cooked [_LEN]int64 = [...]int64{
+       // rngCooked used for seeding. See gen_cooked.go for details.
+       rngCooked [rngLen]int64 = [...]int64{
                -4181792142133755926, -4576982950128230565, 1395769623340756751, 5333664234075297259,
                -6347679516498800754, 9033628115061424579, 7143218595135194537, 4812947590706362721,
                7937252194349799378, 5307299880338848416, 8209348851763925077, -7107630437535961764,
@@ -181,18 +178,24 @@ var (
 )
 
 type rngSource struct {
-       tap  int         // index into vec
-       feed int         // index into vec
-       vec  [_LEN]int64 // current feedback register
+       tap  int           // index into vec
+       feed int           // index into vec
+       vec  [rngLen]int64 // current feedback register
 }
 
 // seed rng x[n+1] = 48271 * x[n] mod (2**31 - 1)
 func seedrand(x int32) int32 {
-       hi := x / _Q
-       lo := x % _Q
-       x = _A*lo - _R*hi
+       const (
+               A = 48271
+               Q = 44488
+               R = 3399
+       )
+
+       hi := x / Q
+       lo := x % Q
+       x = A*lo - R*hi
        if x < 0 {
-               x += _M
+               x += int32max
        }
        return x
 }
@@ -200,18 +203,18 @@ func seedrand(x int32) int32 {
 // Seed uses the provided seed value to initialize the generator to a deterministic state.
 func (rng *rngSource) Seed(seed int64) {
        rng.tap = 0
-       rng.feed = _LEN - _TAP
+       rng.feed = rngLen - rngTap
 
-       seed = seed % _M
+       seed = seed % int32max
        if seed < 0 {
-               seed += _M
+               seed += int32max
        }
        if seed == 0 {
                seed = 89482311
        }
 
        x := int32(seed)
-       for i := -20; i < _LEN; i++ {
+       for i := -20; i < rngLen; i++ {
                x = seedrand(x)
                if i >= 0 {
                        var u int64
@@ -220,7 +223,7 @@ func (rng *rngSource) Seed(seed int64) {
                        u ^= int64(x) << 20
                        x = seedrand(x)
                        u ^= int64(x)
-                       u ^= rng_cooked[i]
+                       u ^= rngCooked[i]
                        rng.vec[i] = u
                }
        }
@@ -228,19 +231,19 @@ func (rng *rngSource) Seed(seed int64) {
 
 // Int63 returns a non-negative pseudo-random 63-bit integer as an int64.
 func (rng *rngSource) Int63() int64 {
-       return int64(rng.Uint64() & _MASK)
+       return int64(rng.Uint64() & rngMask)
 }
 
 // Uint64 returns a non-negative pseudo-random 64-bit integer as an uint64.
 func (rng *rngSource) Uint64() uint64 {
        rng.tap--
        if rng.tap < 0 {
-               rng.tap += _LEN
+               rng.tap += rngLen
        }
 
        rng.feed--
        if rng.feed < 0 {
-               rng.feed += _LEN
+               rng.feed += rngLen
        }
 
        x := rng.vec[rng.feed] + rng.vec[rng.tap]