common/random.go supports seeding and *Rand (#121)

* common/random.go supports seeding and *Rand
* Ensure determinism

common/random.go

@@ -13,34 +13,138 @@ const (
 
 // pseudo random number generator.
 // seeded with OS randomness (crand)
-var prng struct {
+
+type Rand struct {
 	sync.Mutex
 	*mrand.Rand
 }
 
-func reset() {
-	b := cRandBytes(8)
-	var seed uint64
-	for i := 0; i < 8; i++ {
-		seed |= uint64(b[i])
-		seed <<= 8
-	}
-	prng.Lock()
-	prng.Rand = mrand.New(mrand.NewSource(int64(seed)))
-	prng.Unlock()
-}
+var grand *Rand
 
 func init() {
-	reset()
+	grand = New()
+	grand.init()
+}
+
+func New() *Rand {
+	rand := &Rand{}
+	rand.init()
+	return rand
+}
+
+func (r *Rand) init() {
+	bz := cRandBytes(8)
+	var seed uint64
+	for i := 0; i < 8; i++ {
+		seed |= uint64(bz[i])
+		seed <<= 8
+	}
+	r.reset(int64(seed))
+}
+
+func (r *Rand) reset(seed int64) {
+	r.Rand = mrand.New(mrand.NewSource(seed))
+}
+
+//----------------------------------------
+// Global functions
+
+func Seed(seed int64) {
+	grand.Seed(seed)
+}
+
+func RandStr(length int) string {
+	return grand.RandStr(length)
+}
+
+func RandUint16() uint16 {
+	return grand.RandUint16()
+}
+
+func RandUint32() uint32 {
+	return grand.RandUint32()
+}
+
+func RandUint64() uint64 {
+	return grand.RandUint64()
+}
+
+func RandUint() uint {
+	return grand.RandUint()
+}
+
+func RandInt16() int16 {
+	return grand.RandInt16()
+}
+
+func RandInt32() int32 {
+	return grand.RandInt32()
+}
+
+func RandInt64() int64 {
+	return grand.RandInt64()
+}
+
+func RandInt() int {
+	return grand.RandInt()
+}
+
+func RandInt31() int32 {
+	return grand.RandInt31()
+}
+
+func RandInt63() int64 {
+	return grand.RandInt63()
+}
+
+func RandUint16Exp() uint16 {
+	return grand.RandUint16Exp()
+}
+
+func RandUint32Exp() uint32 {
+	return grand.RandUint32Exp()
+}
+
+func RandUint64Exp() uint64 {
+	return grand.RandUint64Exp()
+}
+
+func RandFloat32() float32 {
+	return grand.RandFloat32()
+}
+
+func RandTime() time.Time {
+	return grand.RandTime()
+}
+
+func RandBytes(n int) []byte {
+	return grand.RandBytes(n)
+}
+
+func RandIntn(n int) int {
+	return grand.RandIntn(n)
+}
+
+func RandPerm(n int) []int {
+	return grand.RandPerm(n)
+}
+
+//----------------------------------------
+// Rand methods
+
+func (r *Rand) Seed(seed int64) {
+	r.Lock()
+	r.reset(seed)
+	r.Unlock()
 }
 
 // Constructs an alphanumeric string of given length.
 // It is not safe for cryptographic usage.
-func RandStr(length int) string {
+func (r *Rand) RandStr(length int) string {
 	chars := []byte{}
 MAIN_LOOP:
 	for {
-		val := RandInt63()
+		val := r.RandInt63()
 		for i := 0; i < 10; i++ {
 			v := int(val & 0x3f) // rightmost 6 bits
 			if v >= 62 {         // only 62 characters in strChars
@@ -60,127 +164,127 @@ MAIN_LOOP:
 }
 
 // It is not safe for cryptographic usage.
-func RandUint16() uint16 {
-	return uint16(RandUint32() & (1<<16 - 1))
+func (r *Rand) RandUint16() uint16 {
+	return uint16(r.RandUint32() & (1<<16 - 1))
 }
 
 // It is not safe for cryptographic usage.
-func RandUint32() uint32 {
-	prng.Lock()
-	u32 := prng.Uint32()
-	prng.Unlock()
+func (r *Rand) RandUint32() uint32 {
+	r.Lock()
+	u32 := r.Uint32()
+	r.Unlock()
 	return u32
 }
 
 // It is not safe for cryptographic usage.
-func RandUint64() uint64 {
-	return uint64(RandUint32())<<32 + uint64(RandUint32())
+func (r *Rand) RandUint64() uint64 {
+	return uint64(r.RandUint32())<<32 + uint64(r.RandUint32())
 }
 
 // It is not safe for cryptographic usage.
-func RandUint() uint {
-	prng.Lock()
-	i := prng.Int()
-	prng.Unlock()
+func (r *Rand) RandUint() uint {
+	r.Lock()
+	i := r.Int()
+	r.Unlock()
 	return uint(i)
 }
 
 // It is not safe for cryptographic usage.
-func RandInt16() int16 {
-	return int16(RandUint32() & (1<<16 - 1))
+func (r *Rand) RandInt16() int16 {
+	return int16(r.RandUint32() & (1<<16 - 1))
 }
 
 // It is not safe for cryptographic usage.
-func RandInt32() int32 {
-	return int32(RandUint32())
+func (r *Rand) RandInt32() int32 {
+	return int32(r.RandUint32())
 }
 
 // It is not safe for cryptographic usage.
-func RandInt64() int64 {
-	return int64(RandUint64())
+func (r *Rand) RandInt64() int64 {
+	return int64(r.RandUint64())
 }
 
 // It is not safe for cryptographic usage.
-func RandInt() int {
-	prng.Lock()
-	i := prng.Int()
-	prng.Unlock()
+func (r *Rand) RandInt() int {
+	r.Lock()
+	i := r.Int()
+	r.Unlock()
 	return i
 }
 
 // It is not safe for cryptographic usage.
-func RandInt31() int32 {
-	prng.Lock()
-	i31 := prng.Int31()
-	prng.Unlock()
+func (r *Rand) RandInt31() int32 {
+	r.Lock()
+	i31 := r.Int31()
+	r.Unlock()
 	return i31
 }
 
 // It is not safe for cryptographic usage.
-func RandInt63() int64 {
-	prng.Lock()
-	i63 := prng.Int63()
-	prng.Unlock()
+func (r *Rand) RandInt63() int64 {
+	r.Lock()
+	i63 := r.Int63()
+	r.Unlock()
 	return i63
 }
 
 // Distributed pseudo-exponentially to test for various cases
 // It is not safe for cryptographic usage.
-func RandUint16Exp() uint16 {
-	bits := RandUint32() % 16
+func (r *Rand) RandUint16Exp() uint16 {
+	bits := r.RandUint32() % 16
 	if bits == 0 {
 		return 0
 	}
 	n := uint16(1 << (bits - 1))
-	n += uint16(RandInt31()) & ((1 << (bits - 1)) - 1)
+	n += uint16(r.RandInt31()) & ((1 << (bits - 1)) - 1)
 	return n
 }
 
 // Distributed pseudo-exponentially to test for various cases
 // It is not safe for cryptographic usage.
-func RandUint32Exp() uint32 {
-	bits := RandUint32() % 32
+func (r *Rand) RandUint32Exp() uint32 {
+	bits := r.RandUint32() % 32
 	if bits == 0 {
 		return 0
 	}
 	n := uint32(1 << (bits - 1))
-	n += uint32(RandInt31()) & ((1 << (bits - 1)) - 1)
+	n += uint32(r.RandInt31()) & ((1 << (bits - 1)) - 1)
 	return n
 }
 
 // Distributed pseudo-exponentially to test for various cases
 // It is not safe for cryptographic usage.
-func RandUint64Exp() uint64 {
-	bits := RandUint32() % 64
+func (r *Rand) RandUint64Exp() uint64 {
+	bits := r.RandUint32() % 64
 	if bits == 0 {
 		return 0
 	}
 	n := uint64(1 << (bits - 1))
-	n += uint64(RandInt63()) & ((1 << (bits - 1)) - 1)
+	n += uint64(r.RandInt63()) & ((1 << (bits - 1)) - 1)
 	return n
 }
 
 // It is not safe for cryptographic usage.
-func RandFloat32() float32 {
-	prng.Lock()
-	f32 := prng.Float32()
-	prng.Unlock()
+func (r *Rand) RandFloat32() float32 {
+	r.Lock()
+	f32 := r.Float32()
+	r.Unlock()
 	return f32
 }
 
 // It is not safe for cryptographic usage.
-func RandTime() time.Time {
-	return time.Unix(int64(RandUint64Exp()), 0)
+func (r *Rand) RandTime() time.Time {
+	return time.Unix(int64(r.RandUint64Exp()), 0)
 }
 
 // RandBytes returns n random bytes from the OS's source of entropy ie. via crypto/rand.
 // It is not safe for cryptographic usage.
-func RandBytes(n int) []byte {
+func (r *Rand) RandBytes(n int) []byte {
 	// cRandBytes isn't guaranteed to be fast so instead
 	// use random bytes generated from the internal PRNG
 	bs := make([]byte, n)
 	for i := 0; i < len(bs); i++ {
-		bs[i] = byte(RandInt() & 0xFF)
+		bs[i] = byte(r.RandInt() & 0xFF)
 	}
 	return bs
 }
@@ -188,19 +292,19 @@ func RandBytes(n int) []byte {
 // RandIntn returns, as an int, a non-negative pseudo-random number in [0, n).
 // It panics if n <= 0.
 // It is not safe for cryptographic usage.
-func RandIntn(n int) int {
-	prng.Lock()
-	i := prng.Intn(n)
-	prng.Unlock()
+func (r *Rand) RandIntn(n int) int {
+	r.Lock()
+	i := r.Intn(n)
+	r.Unlock()
 	return i
 }
 
 // RandPerm returns a pseudo-random permutation of n integers in [0, n).
 // It is not safe for cryptographic usage.
-func RandPerm(n int) []int {
-	prng.Lock()
-	perm := prng.Perm(n)
-	prng.Unlock()
+func (r *Rand) RandPerm(n int) []int {
+	r.Lock()
+	perm := r.Perm(n)
+	r.Unlock()
 	return perm
 }