Adding upstream version 1.22.1.upstream/1.22.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 121 insertions, 0 deletions

diff --git a/src/math/rand/v2/pcg.go b/src/math/rand/v2/pcg.go
new file mode 100644
index 0000000..77708d7
--- /dev/null
+++ b/src/math/rand/v2/pcg.go
@@ -0,0 +1,121 @@
+// Copyright 2023 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 (
+	"errors"
+	"math/bits"
+)
+
+// https://numpy.org/devdocs/reference/random/upgrading-pcg64.html
+// https://github.com/imneme/pcg-cpp/commit/871d0494ee9c9a7b7c43f753e3d8ca47c26f8005
+
+// A PCG is a PCG generator with 128 bits of internal state.
+// A zero PCG is equivalent to NewPCG(0, 0).
+type PCG struct {
+	hi uint64
+	lo uint64
+}
+
+// NewPCG returns a new PCG seeded with the given values.
+func NewPCG(seed1, seed2 uint64) *PCG {
+	return &PCG{seed1, seed2}
+}
+
+// Seed resets the PCG to behave the same way as NewPCG(seed1, seed2).
+func (p *PCG) Seed(seed1, seed2 uint64) {
+	p.hi = seed1
+	p.lo = seed2
+}
+
+// binary.bigEndian.Uint64, copied to avoid dependency
+func beUint64(b []byte) uint64 {
+	_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
+	return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
+		uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
+}
+
+// binary.bigEndian.PutUint64, copied to avoid dependency
+func bePutUint64(b []byte, v uint64) {
+	_ = b[7] // early bounds check to guarantee safety of writes below
+	b[0] = byte(v >> 56)
+	b[1] = byte(v >> 48)
+	b[2] = byte(v >> 40)
+	b[3] = byte(v >> 32)
+	b[4] = byte(v >> 24)
+	b[5] = byte(v >> 16)
+	b[6] = byte(v >> 8)
+	b[7] = byte(v)
+}
+
+// MarshalBinary implements the encoding.BinaryMarshaler interface.
+func (p *PCG) MarshalBinary() ([]byte, error) {
+	b := make([]byte, 20)
+	copy(b, "pcg:")
+	bePutUint64(b[4:], p.hi)
+	bePutUint64(b[4+8:], p.lo)
+	return b, nil
+}
+
+var errUnmarshalPCG = errors.New("invalid PCG encoding")
+
+// UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.
+func (p *PCG) UnmarshalBinary(data []byte) error {
+	if len(data) != 20 || string(data[:4]) != "pcg:" {
+		return errUnmarshalPCG
+	}
+	p.hi = beUint64(data[4:])
+	p.lo = beUint64(data[4+8:])
+	return nil
+}
+
+func (p *PCG) next() (hi, lo uint64) {
+	// https://github.com/imneme/pcg-cpp/blob/428802d1a5/include/pcg_random.hpp#L161
+	//
+	// Numpy's PCG multiplies by the 64-bit value cheapMul
+	// instead of the 128-bit value used here and in the official PCG code.
+	// This does not seem worthwhile, at least for Go: not having any high
+	// bits in the multiplier reduces the effect of low bits on the highest bits,
+	// and it only saves 1 multiply out of 3.
+	// (On 32-bit systems, it saves 1 out of 6, since Mul64 is doing 4.)
+	const (
+		mulHi = 2549297995355413924
+		mulLo = 4865540595714422341
+		incHi = 6364136223846793005
+		incLo = 1442695040888963407
+	)
+
+	// state = state * mul + inc
+	hi, lo = bits.Mul64(p.lo, mulLo)
+	hi += p.hi*mulLo + p.lo*mulHi
+	lo, c := bits.Add64(lo, incLo, 0)
+	hi, _ = bits.Add64(hi, incHi, c)
+	p.lo = lo
+	p.hi = hi
+	return hi, lo
+}
+
+// Uint64 return a uniformly-distributed random uint64 value.
+func (p *PCG) Uint64() uint64 {
+	hi, lo := p.next()
+
+	// XSL-RR would be
+	//	hi, lo := p.next()
+	//	return bits.RotateLeft64(lo^hi, -int(hi>>58))
+	// but Numpy uses DXSM and O'Neill suggests doing the same.
+	// See https://github.com/golang/go/issues/21835#issuecomment-739065688
+	// and following comments.
+
+	// DXSM "double xorshift multiply"
+	// https://github.com/imneme/pcg-cpp/blob/428802d1a5/include/pcg_random.hpp#L1015
+
+	// https://github.com/imneme/pcg-cpp/blob/428802d1a5/include/pcg_random.hpp#L176
+	const cheapMul = 0xda942042e4dd58b5
+	hi ^= hi >> 32
+	hi *= cheapMul
+	hi ^= hi >> 48
+	hi *= (lo | 1)
+	return hi
+}