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Move ChaCha8 code into internal/chacha8rand and use it to implement
runtime.rand, which is used for the unseeded global source for
both math/rand and math/rand/v2. This also affects the calculation of
the start point for iteration over very very large maps (when the
32-bit fastrand is not big enough).
The benefit is that misuse of the global random number generators
in math/rand and math/rand/v2 in contexts where non-predictable
randomness is important for security reasons is no longer a
security problem, removing a common mistake among programmers
who are unaware of the different kinds of randomness.
The cost is an extra 304 bytes per thread stored in the m struct
plus 2-3ns more per random uint64 due to the more sophisticated
algorithm. Using PCG looks like it would cost about the same,
although I haven't benchmarked that.
Before this, the math/rand and math/rand/v2 global generator
was wyrand (https://github.com/wangyi-fudan/wyhash).
For math/rand, using wyrand instead of the Mitchell/Reeds/Thompson
ALFG was justifiable, since the latter was not any better.
But for math/rand/v2, the global generator really should be
at least as good as one of the well-studied, specific algorithms
provided directly by the package, and it's not.
(Wyrand is still reasonable for scheduling and cache decisions.)
Good randomness does have a cost: about twice wyrand.
Also rationalize the various runtime rand references.
goos: linux
goarch: amd64
pkg: math/rand/v2
cpu: AMD Ryzen 9 7950X 16-Core Processor
│ bbb48afeb7.amd64 │ 5cf807d1ea.amd64 │
│ sec/op │ sec/op vs base │
ChaCha8-32 1.862n ± 2% 1.861n ± 2% ~ (p=0.825 n=20)
PCG_DXSM-32 1.471n ± 1% 1.460n ± 2% ~ (p=0.153 n=20)
SourceUint64-32 1.636n ± 2% 1.582n ± 1% -3.30% (p=0.000 n=20)
GlobalInt64-32 2.087n ± 1% 3.663n ± 1% +75.54% (p=0.000 n=20)
GlobalInt64Parallel-32 0.1042n ± 1% 0.2026n ± 1% +94.48% (p=0.000 n=20)
GlobalUint64-32 2.263n ± 2% 3.724n ± 1% +64.57% (p=0.000 n=20)
GlobalUint64Parallel-32 0.1019n ± 1% 0.1973n ± 1% +93.67% (p=0.000 n=20)
Int64-32 1.771n ± 1% 1.774n ± 1% ~ (p=0.449 n=20)
Uint64-32 1.863n ± 2% 1.866n ± 1% ~ (p=0.364 n=20)
GlobalIntN1000-32 3.134n ± 3% 4.730n ± 2% +50.95% (p=0.000 n=20)
IntN1000-32 2.489n ± 1% 2.489n ± 1% ~ (p=0.683 n=20)
Int64N1000-32 2.521n ± 1% 2.516n ± 1% ~ (p=0.394 n=20)
Int64N1e8-32 2.479n ± 1% 2.478n ± 2% ~ (p=0.743 n=20)
Int64N1e9-32 2.530n ± 2% 2.514n ± 2% ~ (p=0.193 n=20)
Int64N2e9-32 2.501n ± 1% 2.494n ± 1% ~ (p=0.616 n=20)
Int64N1e18-32 3.227n ± 1% 3.205n ± 1% ~ (p=0.101 n=20)
Int64N2e18-32 3.647n ± 1% 3.599n ± 1% ~ (p=0.019 n=20)
Int64N4e18-32 5.135n ± 1% 5.069n ± 2% ~ (p=0.034 n=20)
Int32N1000-32 2.657n ± 1% 2.637n ± 1% ~ (p=0.180 n=20)
Int32N1e8-32 2.636n ± 1% 2.636n ± 1% ~ (p=0.763 n=20)
Int32N1e9-32 2.660n ± 2% 2.638n ± 1% ~ (p=0.358 n=20)
Int32N2e9-32 2.662n ± 2% 2.618n ± 2% ~ (p=0.064 n=20)
Float32-32 2.272n ± 2% 2.239n ± 2% ~ (p=0.194 n=20)
Float64-32 2.272n ± 1% 2.286n ± 2% ~ (p=0.763 n=20)
ExpFloat64-32 3.762n ± 1% 3.744n ± 1% ~ (p=0.171 n=20)
NormFloat64-32 3.706n ± 1% 3.655n ± 2% ~ (p=0.066 n=20)
Perm3-32 32.93n ± 3% 34.62n ± 1% +5.13% (p=0.000 n=20)
Perm30-32 202.9n ± 1% 204.0n ± 1% ~ (p=0.482 n=20)
Perm30ViaShuffle-32 115.0n ± 1% 114.9n ± 1% ~ (p=0.358 n=20)
ShuffleOverhead-32 112.8n ± 1% 112.7n ± 1% ~ (p=0.692 n=20)
Concurrent-32 2.107n ± 0% 3.725n ± 1% +76.75% (p=0.000 n=20)
goos: darwin
goarch: arm64
pkg: math/rand/v2
│ bbb48afeb7.arm64 │ 5cf807d1ea.arm64 │
│ sec/op │ sec/op vs base │
ChaCha8-8 2.480n ± 0% 2.429n ± 0% -2.04% (p=0.000 n=20)
PCG_DXSM-8 2.531n ± 0% 2.530n ± 0% ~ (p=0.877 n=20)
SourceUint64-8 2.534n ± 0% 2.533n ± 0% ~ (p=0.732 n=20)
GlobalInt64-8 2.172n ± 1% 4.794n ± 0% +120.67% (p=0.000 n=20)
GlobalInt64Parallel-8 0.4320n ± 0% 0.9605n ± 0% +122.32% (p=0.000 n=20)
GlobalUint64-8 2.182n ± 0% 4.770n ± 0% +118.58% (p=0.000 n=20)
GlobalUint64Parallel-8 0.4307n ± 0% 0.9583n ± 0% +122.51% (p=0.000 n=20)
Int64-8 4.107n ± 0% 4.104n ± 0% ~ (p=0.416 n=20)
Uint64-8 4.080n ± 0% 4.080n ± 0% ~ (p=0.052 n=20)
GlobalIntN1000-8 2.814n ± 2% 5.643n ± 0% +100.50% (p=0.000 n=20)
IntN1000-8 4.141n ± 0% 4.139n ± 0% ~ (p=0.140 n=20)
Int64N1000-8 4.140n ± 0% 4.140n ± 0% ~ (p=0.313 n=20)
Int64N1e8-8 4.140n ± 0% 4.139n ± 0% ~ (p=0.103 n=20)
Int64N1e9-8 4.139n ± 0% 4.140n ± 0% ~ (p=0.761 n=20)
Int64N2e9-8 4.140n ± 0% 4.140n ± 0% ~ (p=0.636 n=20)
Int64N1e18-8 5.266n ± 0% 5.326n ± 1% +1.14% (p=0.001 n=20)
Int64N2e18-8 6.052n ± 0% 6.167n ± 0% +1.90% (p=0.000 n=20)
Int64N4e18-8 8.826n ± 0% 9.051n ± 0% +2.55% (p=0.000 n=20)
Int32N1000-8 4.127n ± 0% 4.132n ± 0% +0.12% (p=0.000 n=20)
Int32N1e8-8 4.126n ± 0% 4.131n ± 0% +0.12% (p=0.000 n=20)
Int32N1e9-8 4.127n ± 0% 4.132n ± 0% +0.12% (p=0.000 n=20)
Int32N2e9-8 4.132n ± 0% 4.131n ± 0% ~ (p=0.017 n=20)
Float32-8 4.109n ± 0% 4.105n ± 0% ~ (p=0.379 n=20)
Float64-8 4.107n ± 0% 4.106n ± 0% ~ (p=0.867 n=20)
ExpFloat64-8 5.339n ± 0% 5.383n ± 0% +0.82% (p=0.000 n=20)
NormFloat64-8 5.735n ± 0% 5.737n ± 1% ~ (p=0.856 n=20)
Perm3-8 26.65n ± 0% 26.80n ± 1% +0.58% (p=0.000 n=20)
Perm30-8 194.8n ± 1% 197.0n ± 0% +1.18% (p=0.000 n=20)
Perm30ViaShuffle-8 156.6n ± 0% 157.6n ± 1% +0.61% (p=0.000 n=20)
ShuffleOverhead-8 124.9n ± 0% 125.5n ± 0% +0.52% (p=0.000 n=20)
Concurrent-8 2.434n ± 3% 5.066n ± 0% +108.09% (p=0.000 n=20)
goos: linux
goarch: 386
pkg: math/rand/v2
cpu: AMD Ryzen 9 7950X 16-Core Processor
│ bbb48afeb7.386 │ 5cf807d1ea.386 │
│ sec/op │ sec/op vs base │
ChaCha8-32 11.295n ± 1% 4.748n ± 2% -57.96% (p=0.000 n=20)
PCG_DXSM-32 7.693n ± 1% 7.738n ± 2% ~ (p=0.542 n=20)
SourceUint64-32 7.658n ± 2% 7.622n ± 2% ~ (p=0.344 n=20)
GlobalInt64-32 3.473n ± 2% 7.526n ± 2% +116.73% (p=0.000 n=20)
GlobalInt64Parallel-32 0.3198n ± 0% 0.5444n ± 0% +70.22% (p=0.000 n=20)
GlobalUint64-32 3.612n ± 0% 7.575n ± 1% +109.69% (p=0.000 n=20)
GlobalUint64Parallel-32 0.3168n ± 0% 0.5403n ± 0% +70.51% (p=0.000 n=20)
Int64-32 7.673n ± 2% 7.789n ± 1% ~ (p=0.122 n=20)
Uint64-32 7.773n ± 1% 7.827n ± 2% ~ (p=0.920 n=20)
GlobalIntN1000-32 6.268n ± 1% 9.581n ± 1% +52.87% (p=0.000 n=20)
IntN1000-32 10.33n ± 2% 10.45n ± 1% ~ (p=0.233 n=20)
Int64N1000-32 10.98n ± 2% 11.01n ± 1% ~ (p=0.401 n=20)
Int64N1e8-32 11.19n ± 2% 10.97n ± 1% ~ (p=0.033 n=20)
Int64N1e9-32 11.06n ± 1% 11.08n ± 1% ~ (p=0.498 n=20)
Int64N2e9-32 11.10n ± 1% 11.01n ± 2% ~ (p=0.995 n=20)
Int64N1e18-32 15.23n ± 2% 15.04n ± 1% ~ (p=0.973 n=20)
Int64N2e18-32 15.89n ± 1% 15.85n ± 1% ~ (p=0.409 n=20)
Int64N4e18-32 18.96n ± 2% 19.34n ± 2% ~ (p=0.048 n=20)
Int32N1000-32 10.46n ± 2% 10.44n ± 2% ~ (p=0.480 n=20)
Int32N1e8-32 10.46n ± 2% 10.49n ± 2% ~ (p=0.951 n=20)
Int32N1e9-32 10.28n ± 2% 10.26n ± 1% ~ (p=0.431 n=20)
Int32N2e9-32 10.50n ± 2% 10.44n ± 2% ~ (p=0.249 n=20)
Float32-32 13.80n ± 2% 13.80n ± 2% ~ (p=0.751 n=20)
Float64-32 23.55n ± 2% 23.87n ± 0% ~ (p=0.408 n=20)
ExpFloat64-32 15.36n ± 1% 15.29n ± 2% ~ (p=0.316 n=20)
NormFloat64-32 13.57n ± 1% 13.79n ± 1% +1.66% (p=0.005 n=20)
Perm3-32 45.70n ± 2% 46.99n ± 2% +2.81% (p=0.001 n=20)
Perm30-32 399.0n ± 1% 403.8n ± 1% +1.19% (p=0.006 n=20)
Perm30ViaShuffle-32 349.0n ± 1% 350.4n ± 1% ~ (p=0.909 n=20)
ShuffleOverhead-32 322.3n ± 1% 323.8n ± 1% ~ (p=0.410 n=20)
Concurrent-32 3.331n ± 1% 7.312n ± 1% +119.50% (p=0.000 n=20)
For #61716.
Change-Id: Ibdddeed85c34d9ae397289dc899e04d4845f9ed2
Reviewed-on: https://go-review.googlesource.com/c/go/+/516860
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
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