summaryrefslogtreecommitdiffstats
path: root/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/rng.go
diff options
context:
space:
mode:
Diffstat (limited to 'dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/rng.go')
-rw-r--r--dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/rng.go91
1 files changed, 91 insertions, 0 deletions
diff --git a/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/rng.go b/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/rng.go
new file mode 100644
index 0000000..9b79108
--- /dev/null
+++ b/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/rng.go
@@ -0,0 +1,91 @@
+// Copyright 2017 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
+
+import (
+ "encoding/binary"
+ "io"
+ "math/bits"
+)
+
+// PCGSource is an implementation of a 64-bit permuted congruential
+// generator as defined in
+//
+// PCG: A Family of Simple Fast Space-Efficient Statistically Good
+// Algorithms for Random Number Generation
+// Melissa E. O’Neill, Harvey Mudd College
+// http://www.pcg-random.org/pdf/toms-oneill-pcg-family-v1.02.pdf
+//
+// The generator here is the congruential generator PCG XSL RR 128/64 (LCG)
+// as found in the software available at http://www.pcg-random.org/.
+// It has period 2^128 with 128 bits of state, producing 64-bit values.
+// Is state is represented by two uint64 words.
+type PCGSource struct {
+ low uint64
+ high uint64
+}
+
+const (
+ maxUint32 = (1 << 32) - 1
+
+ multiplier = 47026247687942121848144207491837523525
+ mulHigh = multiplier >> 64
+ mulLow = multiplier & maxUint64
+
+ increment = 117397592171526113268558934119004209487
+ incHigh = increment >> 64
+ incLow = increment & maxUint64
+
+ // TODO: Use these?
+ initializer = 245720598905631564143578724636268694099
+ initHigh = initializer >> 64
+ initLow = initializer & maxUint64
+)
+
+// Seed uses the provided seed value to initialize the generator to a deterministic state.
+func (pcg *PCGSource) Seed(seed uint64) {
+ pcg.low = seed
+ pcg.high = seed // TODO: What is right?
+}
+
+// Uint64 returns a pseudo-random 64-bit unsigned integer as a uint64.
+func (pcg *PCGSource) Uint64() uint64 {
+ pcg.multiply()
+ pcg.add()
+ // XOR high and low 64 bits together and rotate right by high 6 bits of state.
+ return bits.RotateLeft64(pcg.high^pcg.low, -int(pcg.high>>58))
+}
+
+func (pcg *PCGSource) add() {
+ var carry uint64
+ pcg.low, carry = bits.Add64(pcg.low, incLow, 0)
+ pcg.high, _ = bits.Add64(pcg.high, incHigh, carry)
+}
+
+func (pcg *PCGSource) multiply() {
+ hi, lo := bits.Mul64(pcg.low, mulLow)
+ hi += pcg.high * mulLow
+ hi += pcg.low * mulHigh
+ pcg.low = lo
+ pcg.high = hi
+}
+
+// MarshalBinary returns the binary representation of the current state of the generator.
+func (pcg *PCGSource) MarshalBinary() ([]byte, error) {
+ var buf [16]byte
+ binary.BigEndian.PutUint64(buf[:8], pcg.high)
+ binary.BigEndian.PutUint64(buf[8:], pcg.low)
+ return buf[:], nil
+}
+
+// UnmarshalBinary sets the state of the generator to the state represented in data.
+func (pcg *PCGSource) UnmarshalBinary(data []byte) error {
+ if len(data) < 16 {
+ return io.ErrUnexpectedEOF
+ }
+ pcg.low = binary.BigEndian.Uint64(data[8:])
+ pcg.high = binary.BigEndian.Uint64(data[:8])
+ return nil
+}