Commit Graph

56 Commits

Author SHA1 Message Date
Russ Cox 213495a4a6 internal/godebug: export non-default-behavior counters in runtime/metrics
Allow GODEBUG users to report how many times a setting
resulted in non-default behavior.

Record non-default-behaviors for all existing GODEBUGs.

Also rework tests to ensure that runtime is in sync with runtime/metrics.All,
and generate docs mechanically from metrics.All.

For #56986.

Change-Id: Iefa1213e2a5c3f19ea16cd53298c487952ef05a4
Reviewed-on: https://go-review.googlesource.com/c/go/+/453618
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
2023-01-19 22:26:43 +00:00
Russ Cox ad7dc8ad55 math/rand: deprecate Seed
Programs that call Seed and then expect a specific sequence
of results from the global random source (using functions such as Int)
can be broken when a dependency changes how much it consumes
from the global random source. To avoid such breakages, programs
that need a specific result sequence should use NewRand(NewSource(seed))
to obtain a random generator that other packages cannot access.

Fixes #56319.

Change-Id: Idac33991b719d2c71f109f51dacb3467a649e01e
Reviewed-on: https://go-review.googlesource.com/c/go/+/451375
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
2022-11-16 21:21:22 +00:00
Russ Cox ea4631cc0c internal/godebug: define more efficient API
We have been expanding our use of GODEBUG for compatibility,
and the current implementation forces a tradeoff between
freshness and efficiency. It parses the environment variable
in full each time it is called, which is expensive. But if clients
cache the result, they won't respond to run-time GODEBUG
changes, as happened with x509sha1 (#56436).

This CL changes the GODEBUG API to provide efficient,
up-to-date results. Instead of a single Get function,
New returns a *godebug.Setting that itself has a Get method.
Clients can save the result of New, which is no more expensive
than errors.New, in a global variable, and then call that
variable's Get method to get the value. Get costs only two
atomic loads in the case where the variable hasn't changed
since the last call.

Unfortunately, these changes do require importing sync
from godebug, which will mean that sync itself will never
be able to use a GODEBUG setting. That doesn't seem like
such a hardship. If it was really necessary, the runtime could
pass a setting to package sync itself at startup, with the
caveat that that setting, like the ones used by runtime itself,
would not respond to run-time GODEBUG changes.

Change-Id: I99a3acfa24fb2a692610af26a5d14bbc62c966ac
Reviewed-on: https://go-review.googlesource.com/c/go/+/449504
Run-TryBot: Russ Cox <rsc@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
2022-11-14 15:19:57 +00:00
hopehook 599a1e40c6 math/rand: deprecate Read
For #20661.

Change-Id: I1e638cb619e643eadc210d71f92bd1af7bafc912
Reviewed-on: https://go-review.googlesource.com/c/go/+/436955
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: hopehook <hopehook@golangcn.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
2022-10-27 04:32:55 +00:00
Russ Cox 3afba3124d all: remove uses of rand.Seed
As of CL 443058, rand.Seed is not necessary to call,
nor is it a particular good idea.

For #54880.

Change-Id: If9d70763622c09008599db8c97a90fcbe285c6f8
Reviewed-on: https://go-review.googlesource.com/c/go/+/445395
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
2022-10-26 16:24:57 +00:00
Russ Cox 90a67d052e math/rand: auto-seed global source
Implement proposal #54880, to automatically seed the global source.

The justification for this not being a breaking change is that any
use of the global source in a package's init function or exported API
clearly must be valid - that is, if a package changes how much
randomness it consumes at init time or in an exported API, that
clearly isn't the kind of breaking change that requires issuing a v2
of that package. That kind of per-package change in the position
of the global source is indistinguishable from seeding the global
source differently. So if the per-package change is valid, so is auto-seeding.

And then, of course, auto-seeding means that packages will be
far less likely to depend on the specific results of the global source
and therefore not break when those kinds of per-package changes
happen in the future.

Seed(1) can be called in programs that need the old sequence from
the global source and want to restore the old behavior.
Of course, those programs will still be broken by the per-package
changes just described, and it would be better for them to allocate
local sources rather than continue to use the global one.

Fixes #54880.

Change-Id: Ib9dc3307b97f7a45587a9cc50d81f919d3edc7ae
Reviewed-on: https://go-review.googlesource.com/c/go/+/443058
Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
2022-10-25 16:49:48 +00:00
Russ Cox 7cf06f070e math/rand: refactor to delay allocation of global source
This sets up for delaying the decision of which seed to use,
but this CL still keeps the original global Seed(1) semantics.

Preparation for #54880.

Change-Id: Ibfa9d50ec9023aa755a83852e55168fa7d24b115
Reviewed-on: https://go-review.googlesource.com/c/go/+/443057
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
2022-10-18 14:49:46 +00:00
Jonathan FOng 8e35910640 math/rand: document that Source returned by NewSource implements Source64
Fixes #44488

Change-Id: I570950799788678b9dc6e9ddad894973b4611e09
Reviewed-on: https://go-review.googlesource.com/c/go/+/425974
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: David Chase <drchase@google.com>
2022-09-02 05:05:13 +00:00
Russ Cox 19309779ac all: gofmt main repo
[This CL is part of a sequence implementing the proposal #51082.
The design doc is at https://go.dev/s/godocfmt-design.]

Run the updated gofmt, which reformats doc comments,
on the main repository. Vendored files are excluded.

For #51082.

Change-Id: I7332f099b60f716295fb34719c98c04eb1a85407
Reviewed-on: https://go-review.googlesource.com/c/go/+/384268
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2022-04-11 16:34:30 +00:00
Russ Cox 690ac4071f all: remove trailing blank doc comment lines
A future change to gofmt will rewrite

	// Doc comment.
	//
	func f()

to

	// Doc comment.
	func f()

Apply that change preemptively to all doc comments.

For #51082.

Change-Id: I4023e16cfb0729b64a8590f071cd92f17343081d
Reviewed-on: https://go-review.googlesource.com/c/go/+/384259
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
2022-04-01 18:18:07 +00:00
Russ Cox 2580d0e08d all: gofmt -w -r 'interface{} -> any' src
And then revert the bootstrap cmd directories and certain testdata.
And adjust tests as needed.

Not reverting the changes in std that are bootstrapped,
because some of those changes would appear in API docs,
and we want to use any consistently.
Instead, rewrite 'any' to 'interface{}' in cmd/dist for those directories
when preparing the bootstrap copy.

A few files changed as a result of running gofmt -w
not because of interface{} -> any but because they
hadn't been updated for the new //go:build lines.

Fixes #49884.

Change-Id: Ie8045cba995f65bd79c694ec77a1b3d1fe01bb09
Reviewed-on: https://go-review.googlesource.com/c/go/+/368254
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
2021-12-13 18:45:54 +00:00
Russ Cox f229e7031a all: go fix -fix=buildtag std cmd (except for bootstrap deps, vendor)
When these packages are released as part of Go 1.18,
Go 1.16 will no longer be supported, so we can remove
the +build tags in these files.

Ran go fix -fix=buildtag std cmd and then reverted the bootstrapDirs
as defined in src/cmd/dist/buildtool.go, which need to continue
to build with Go 1.4 for now.

Also reverted src/vendor and src/cmd/vendor, which will need
to be updated in their own repos first.

Manual changes in runtime/pprof/mprof_test.go to adjust line numbers.

For #41184.

Change-Id: Ic0f93f7091295b6abc76ed5cd6e6746e1280861e
Reviewed-on: https://go-review.googlesource.com/c/go/+/344955
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
2021-10-28 18:17:57 +00:00
Russ Cox a294e4e798 math/rand: mention half-open intervals explicitly
If someone sees "in [0,n)" it might look like a typo.
Saying "in the half-open interval [0,n)" will give people
something to search the web for (half-open interval).

Change-Id: I3c343f0a7171891e106e709ca77ab9db5daa5c84
Reviewed-on: https://go-review.googlesource.com/c/go/+/328210
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
2021-06-16 16:38:43 +00:00
Paschalis Tsilias cbb3f09047 testing: add -shuffle=off|on|N to alter the execution order of tests and benchmarks
This CL adds a new flag to the testing package and the go test command
which randomizes the execution order for tests and benchmarks.
This can be useful for identifying unwanted dependencies
between test or benchmark functions.
The flag is off by default. If `-shuffle` is set to `on` then the system
clock will be used as the seed value. If `-shuffle` is set to an integer
N, then N will be used as the seed value. In both cases, the seed will
be reported for failed runs so that they can reproduced later on.

Fixes #28592

Change-Id: I62e7dfae5f63f97a0cbd7830ea844d9f7beac335
Reviewed-on: https://go-review.googlesource.com/c/go/+/310033
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Bryan C. Mills <bcmills@google.com>
2021-04-28 16:06:21 +00:00
Filippo Valsorda d2f96f2f75 math/rand: make the security warning clearer and more prominent
It is still a common misconception that math/rand can be used for
security-sensitive work if seeded with crypto/rand
(lazyledger/lazyledger-core#270). It can not.

Change-Id: I8598c352d1750eabeada50be9976ab68cbb42cc0
Reviewed-on: https://go-review.googlesource.com/c/go/+/310350
Trust: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
2021-04-23 17:50:33 +00:00
Russ Cox d4b2638234 all: go fmt std cmd (but revert vendor)
Make all our package sources use Go 1.17 gofmt format
(adding //go:build lines).

Part of //go:build change (#41184).
See https://golang.org/design/draft-gobuild

Change-Id: Ia0534360e4957e58cd9a18429c39d0e32a6addb4
Reviewed-on: https://go-review.googlesource.com/c/go/+/294430
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2021-02-20 03:54:50 +00:00
Toasa 9eef49cfa6 math/rand: fix typo in comment
Change-Id: I57fbabf272bdfd61918db155ee6f7091f18e5979
GitHub-Last-Rev: e138804b1a
GitHub-Pull-Request: golang/go#43495
Reviewed-on: https://go-review.googlesource.com/c/go/+/281373
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Alberto Donizetti <alb.donizetti@gmail.com>
2021-01-04 17:59:30 +00:00
Brad Fitzpatrick 7d1d944626 math/rand: update comment to avoid use of ^ for exponentiation
Fixes #35920

Change-Id: I1a4d26c5f7f3fbd4de13fc337de482667d83c47f
Reviewed-on: https://go-review.googlesource.com/c/go/+/209758
Reviewed-by: Alberto Donizetti <alb.donizetti@gmail.com>
2019-12-04 21:14:24 +00:00
Carlo Alberto Ferraris 5f1aeaeb77 math/rand: devirtualize interface call in Read
This allows to inline the common case in which the Source is a
rngSource. On linux/amd64 in a VM:

name        old time/op  new time/op  delta
Read3-4     33.8ns ± 8%  18.5ns ± 8%  -45.38%  (p=0.000 n=10+10)
Read64-4     371ns ± 8%    70ns ± 7%  -81.00%  (p=0.000 n=10+10)
Read1000-4  5.33µs ± 5%  0.86µs ± 3%  -83.85%  (p=0.000 n=9+9)

Change-Id: Ibf47b0e9ecdfe62ffcb66d6a92f191800bdc740e
Reviewed-on: https://go-review.googlesource.com/c/go/+/191539
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>
2019-09-30 15:43:34 +00:00
Carlo Alberto Ferraris 931365763a math/rand: devirtualize interface in lockedSource
Avoid interface calls, enable inlining, and store the rngSource close to the
Mutex to exploit better memory locality.

Also add a benchmark to properly measure the threadsafe nature of globalRand.

On a linux/amd64 VM:

name                       old time/op  new time/op  delta
Int63Threadsafe-4          36.4ns ±12%  20.6ns ±11%  -43.52%  (p=0.000 n=30+30)
Int63ThreadsafeParallel-4  79.3ns ± 5%  56.5ns ± 5%  -28.69%  (p=0.000 n=29+30)

Change-Id: I6ab912c1a1e9afc7bacd8e72c82d4d50d546a510
Reviewed-on: https://go-review.googlesource.com/c/go/+/191538
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2019-09-29 14:27:05 +00:00
Russ Cox 06b0babf31 all: shorten some tests
Shorten some of the longest tests that run during all.bash.
Removes 7r 50u 21s from all.bash.

After this change, all.bash is under 5 minutes again on my laptop.

For #26473.

Change-Id: Ie0460aa935808d65460408feaed210fbaa1d5d79
Reviewed-on: https://go-review.googlesource.com/c/go/+/177559
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2019-05-22 12:54:00 +00:00
Vladimir Kovpak 9a8979deb0 math/rand: add example for Intn func
Change-Id: I831ffb5c3fa2872d71def8d8461f0adbd4ae2c1a
GitHub-Last-Rev: 2adfcd2d5a
GitHub-Pull-Request: golang/go#30706
Reviewed-on: https://go-review.googlesource.com/c/go/+/166426
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2019-03-25 16:05:37 +00:00
Benjamin Cable 669ac1228a math/rand: improve package documentation
Notify readers that interval notation is used.
Fixes: #26765

Change-Id: Id02a7fcffbf41699e85631badeee083f5d4b2201
Reviewed-on: https://go-review.googlesource.com/127549
Reviewed-by: Rob Pike <r@golang.org>
2018-08-03 23:08:42 +00:00
Tim Cooper 161874da2a all: update comment URLs from HTTP to HTTPS, where possible
Each URL was manually verified to ensure it did not serve up incorrect
content.

Change-Id: I4dc846227af95a73ee9a3074d0c379ff0fa955df
Reviewed-on: https://go-review.googlesource.com/115798
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
2018-06-01 21:52:00 +00:00
Agniva De Sarker f94b5a8105 math/rand: clarify documentation for Seed example
Fixes #25325

Change-Id: I101641be99a820722edb7272918e04e8d2e1646c
Reviewed-on: https://go-review.googlesource.com/112775
Reviewed-by: Rob Pike <r@golang.org>
2018-05-12 06:21:01 +00:00
weeellz a2ffe3e625 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>
2018-04-16 22:22:14 +00:00
Robert Griesemer 542ea5ad91 go/printer, gofmt: tuned table alignment for better results
The go/printer (and thus gofmt) uses a heuristic to determine
whether to break alignment between elements of an expression
list which is spread across multiple lines. The heuristic only
kicked in if the entry sizes (character length) was above a
certain threshold (20) and the ratio between the previous and
current entry size was above a certain value (4).

This heuristic worked reasonably most of the time, but also
led to unfortunate breaks in many cases where a single entry
was suddenly much smaller (or larger) then the previous one.

The behavior of gofmt was sufficiently mysterious in some of
these situations that many issues were filed against it.

The simplest solution to address this problem is to remove
the heuristic altogether and have a programmer introduce
empty lines to force different alignments if it improves
readability. The problem with that approach is that the
places where it really matters, very long tables with many
(hundreds, or more) entries, may be machine-generated and
not "post-processed" by a human (e.g., unicode/utf8/tables.go).

If a single one of those entries is overlong, the result
would be that the alignment would force all comments or
values in key:value pairs to be adjusted to that overlong
value, making the table hard to read (e.g., that entry may
not even be visible on screen and all other entries seem
spaced out too wide).

Instead, we opted for a slightly improved heuristic that
behaves much better for "normal", human-written code.

1) The threshold is increased from 20 to 40. This disables
the heuristic for many common cases yet even if the alignment
is not "ideal", 40 is not that many characters per line with
todays screens, making it very likely that the entire line
remains "visible" in an editor.

2) Changed the heuristic to not simply look at the size ratio
between current and previous line, but instead considering the
geometric mean of the sizes of the previous (aligned) lines.
This emphasizes the "overall picture" of the previous lines,
rather than a single one (which might be an outlier).

3) Changed the ratio from 4 to 2.5. Now that we ignore sizes
below 40, a ratio of 4 would mean that a new entry would have
to be 4 times bigger (160) or smaller (10) before alignment
would be broken. A ratio of 2.5 seems more sensible.

Applied updated gofmt to all of src and misc. Also tested
against several former issues that complained about this
and verified that the output for the given examples is
satisfactory (added respective test cases).

Some of the files changed because they were not gofmt-ed
in the first place.

For #644.
For #7335.
For #10392.
(and probably more related issues)

Fixes #22852.

Change-Id: I5e48b3d3b157a5cf2d649833b7297b33f43a6f6e
2018-04-04 13:39:34 -07:00
Paul PISCUC 3526c40979 math/rand: typo fixed in documentation of seedPos
In the comment of seedPost, the word: condiiton was changed to: condition

Change-Id: I8967cc0e9f5d37776bada96cc1443c8bf46e1117
Reviewed-on: https://go-review.googlesource.com/86156
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2018-01-04 20:27:29 +00:00
Russ Cox d9a198c7d0 Revert "math/rand: make Perm match Shuffle"
This reverts CL 55972.

Reason for revert: this changes Perm's behavior unnecessarily.
I asked for this change originally but I now regret it.
Reverting so that I don't have to justify it in Go 1.10 release notes.

Edited to keep the change to rand_test.go, which seems to have
been mostly unrelated.

Fixes #22744.

Change-Id: If8bb1bcde3ced0db2fdcd0aa65ab128613686c66
Reviewed-on: https://go-review.googlesource.com/78195
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2017-11-16 16:24:30 +00:00
Burak Guven 9cc170f9a5 math/rand: fix comment for Shuffle
Shuffle panics if n < 0, not n <= 0. The comment for the (*Rand).Shuffle
function is already accurate.

Change-Id: I073049310bca9632e50e9ca3ff79eec402122793
Reviewed-on: https://go-review.googlesource.com/63750
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2017-09-14 03:41:35 +00:00
Ian Lance Taylor 44f7fd030f math/rand: change http to https in comment
Change-Id: I19c1b0e1b238dda82e69bd47459528ed06b55840
Reviewed-on: https://go-review.googlesource.com/62310
Reviewed-by: David Crawshaw <crawshaw@golang.org>
2017-09-08 22:11:55 +00:00
Josh Bleecher Snyder caae0917bf math/rand: make Perm match Shuffle
Perm and Shuffle are fundamentally doing the same work.
This change makes Perm's algorithm match Shuffle's.
In addition to allowing developers to switch more
easily between the two methods, it affords a nice speed-up:

name      old time/op  new time/op  delta
Perm3-8   75.7ns ± 1%  51.8ns ± 1%  -31.59%  (p=0.000 n=9+8)
Perm30-8   610ns ± 1%   405ns ± 1%  -33.67%  (p=0.000 n=9+9)

This change alters the output from Perm,
given the same Source and seed.
This is a change from Go 1.0 behavior.
This necessitates updating the regression test.

This also changes the number of calls made to the Source
during Perm, which changes the output of the math/rand examples.

This also slightly perturbs the output of Perm,
nudging it out of the range currently accepted by TestUniformFactorial.
However, it is complete unclear that the helpers relied on
by TestUniformFactorial are correct. That is #21211.
This change updates checkSimilarDistribution to respect
closeEnough for standard deviations, which makes the test pass.
The whole situation is muddy; see #21211 for details.

There is an alternative implementation of Perm
that avoids initializing m, which is more similar
to the existing implementation, plus some optimizations:

func (r *Rand) Perm(n int) []int {
	m := make([]int, n)
	max31 := n
	if n > 1<<31-1-1 {
		max31 = 1<<31 - 1 - 1
	}
	i := 1
	for ; i < max31; i++ {
		j := r.int31n(int32(i + 1))
		m[i] = m[j]
		m[j] = i
	}
	for ; i < n; i++ {
		j := r.Int63n(int64(i + 1))
		m[i] = m[j]
		m[j] = i
	}
	return m
}

This is a tiny bit faster than the implementation
actually used in this change:

name      old time/op  new time/op  delta
Perm3-8   51.8ns ± 1%  50.3ns ± 1%  -2.83%  (p=0.000 n=8+9)
Perm30-8   405ns ± 1%   394ns ± 1%  -2.66%  (p=0.000 n=9+8)

However, 3% in performance doesn't seem worth
having the two algorithms diverge,
nor the reduced readability of this alternative.

Updates #16213.

Change-Id: I11a7441ff8837ee9c241b4c88f7aa905348be781
Reviewed-on: https://go-review.googlesource.com/55972
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
2017-09-08 13:26:20 +00:00
Josh Bleecher Snyder a2dfe5d278 math/rand: add Shuffle
Shuffle uses the Fisher-Yates algorithm.

Since this is new API, it affords us the opportunity
to use a much faster Int31n implementation that mostly avoids division.
As a result, BenchmarkPerm30ViaShuffle is
about 30% faster than BenchmarkPerm30,
despite requiring a separate initialization loop
and using function calls to swap elements.

Fixes #20480
Updates #16213
Updates #21211

Change-Id: Ib8956c4bebed9d84f193eb98282ec16ee7c2b2d5
Reviewed-on: https://go-review.googlesource.com/51891
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2017-09-08 13:03:02 +00:00
Josh Bleecher Snyder 6b53dd4f2b math/rand: use t.Helper in tests
Change-Id: Iece39e6412c0f6c63f563eed1621b8cca02de835
Reviewed-on: https://go-review.googlesource.com/51890
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Avelino <t@avelino.xxx>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2017-08-08 23:49:31 +00:00
Josh Bleecher Snyder ca19f2fc78 math/rand: fix uniform distribution stddev in tests
The standard deviation of a uniform distribution is size / √12.
The size of the interval [0, 255] is 256, not 255.
While we're here, simplify the expression.

The tests previously passed only because the error margin was large enough.
Sample observed standard deviations while running tests:

73.7893634666819
73.9221651548294
73.8077961697150
73.9084236069471
73.8968446814785
73.8684209136244
73.9774618960282
73.9523483202549

255 / √12 == 73.6121593216772
256 / √12 == 73.9008344562721

Change-Id: I7bc6cdc11e5d098951f2f2133036f62489275979
Reviewed-on: https://go-review.googlesource.com/51310
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2017-08-08 23:49:00 +00:00
Aditya Mukerjee a83d0175a8 math/rand: add concurrency warning to overview comment
Change-Id: I52efa7aa72a23256e5ca56470ffeba975ed8f739
Reviewed-on: https://go-review.googlesource.com/48760
Reviewed-by: Bryan Mills <bcmills@google.com>
2017-07-15 20:34:17 +00:00
Russ Cox 3f69822a9a math/rand: export Source64, mainly for documentation value
There is some code value too: types intending to implement
Source64 can write a conversion confirming that.

For #4254 and the Go 1.8 release notes.

Change-Id: I7fc350a84f3a963e4dab317ad228fa340dda5c66
Reviewed-on: https://go-review.googlesource.com/33456
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2016-11-23 04:29:25 +00:00
Brad Fitzpatrick d8b14c5243 math/rand: make floating point tests shorter on mips and mipsle
Like GOARM=5 does.

Fixes #17944

Change-Id: Ica2a54a90fbd4a29471d1c6009ace2fcc5e82a73
Reviewed-on: https://go-review.googlesource.com/33326
Reviewed-by: Cherry Zhang <cherryyz@google.com>
2016-11-16 19:22:53 +00:00
Florian Uekermann 003a598bf2 math/rand: add Rand.Uint64
This adds Uint64 methods to Rand and rngSource.
Rand.Uint64 uses Source.Uint64 directly if it is present.

rngSource.Uint64 provides access to all 64 bits generated by the
underlying ALFG. To ensure high seed quality a 64th bit has been added
to all elements of the array of "cooked" random numbers that are used
for seeding. gen_cooked.go generates both the 63 bit and 64 bit array.

Fixes #4254

Change-Id: I22855618ac69abae3d2799b3e7e59996d4c5a4b1
Reviewed-on: https://go-review.googlesource.com/27253
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2016-10-03 15:04:39 +00:00
David Glasser 82bc0d4e80 math/rand: document that NewSource sources race
While it was previously explicitly documented that "the default Source"
is safe for concurrent use, a careless reader can interpret that as
meaning "the implementation of the Source interface created by functions
in this package" rather than "the default shared Source used by
top-level functions". Be explicit that the Source returned by NewSource
is not safe for use by multiple goroutines.

Fixes #3611.

Change-Id: Iae4bc04c3887ad6e2491e36e38feda40324022c5
Reviewed-on: https://go-review.googlesource.com/25501
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2016-09-02 05:16:21 +00:00
Florian Uekermann 507144c011 math/rand: Document origin of cooked pseudo-random numbers
The Source provided by math/rand relies on an array of cooked
pseudo-random 63bit integers for seeding. The origin of these
numbers is undocumented.

Add a standalone program in math/rand folder that generates
the 63bit integer array as well as a 64bit version supporting
extension of the Source to 64bit pseudo-random number
generation while maintaining the current sequence in the
lower 63bit.

The code is largely based on the initial implementation of the
random number generator in the go repository by Ken Thompson
(revision 399).

Change-Id: Ib4192aea8127595027116a0f5a7be53f11dc110b
Reviewed-on: https://go-review.googlesource.com/22230
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2016-08-17 14:50:18 +00:00
Ian Lance Taylor fb3cf5c686 math/rand: fix raciness in Rand.Read
There are no synchronization points protecting the readVal and readPos
variables. This leads to a race when Read is called concurrently.
Fix this by adding methods to lockedSource, which is the case where
a race matters.

Fixes #16308.

Change-Id: Ic028909955700906b2d71e5c37c02da21b0f4ad9
Reviewed-on: https://go-review.googlesource.com/24852
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
2016-07-11 15:11:44 +00:00
Dmitri Popov 8d966bad6e math/rand: fix io.Reader implementation
Do not throw away the rest of Int63 value used for
generation random bytes. Save it in Rand struct and
re-use during the next Read call.

Fixes #16124

Change-Id: Ic70bd80c3c3a6590e60ac615e8b3c2324589bea3
Reviewed-on: https://go-review.googlesource.com/24251
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2016-06-27 22:18:09 +00:00
Konstantin Shaposhnikov 33fa855e6c math/rand: fix comment about bits of seed used by the default Source
Fixes #15788

Change-Id: I5a1fd1e5992f1c16cf8d8437d742bf02e1653b9c
Reviewed-on: https://go-review.googlesource.com/23461
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2016-06-26 05:00:39 +00:00
Jeff R. Allen 3474610fbc math/rand: Doc fix for how many bits Seed uses
Document the fact that the default Source uses only
the bottom 31 bits of the given seed.

Fixes #15788

Change-Id: If20d1ec44a55c793a4a0a388f84b9392c2102bd1
Reviewed-on: https://go-review.googlesource.com/23352
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2016-05-24 19:07:46 +00:00
Brady Catherman 9323de3da7 testing: implement 'Unordered Output' in Examples.
Adds a type of output to Examples that allows tests to have unordered
output. This is intended to help clarify when the output of a command
will produce a fixed return, but that return might not be in an constant
order.

Examples where this is useful would be documenting the rand.Perm()
call, or perhaps the (os.File).Readdir(), both of which can not guarantee
order, but can guarantee the elements of the output.

Fixes #10149

Change-Id: Iaf0cf1580b686afebd79718ed67ea744f5ed9fc5
Reviewed-on: https://go-review.googlesource.com/19280
Reviewed-by: Andrew Gerrand <adg@golang.org>
2016-03-09 04:34:41 +00:00
Brad Fitzpatrick 519474451a all: make copyright headers consistent with one space after period
This is a subset of https://golang.org/cl/20022 with only the copyright
header lines, so the next CL will be smaller and more reviewable.

Go policy has been single space after periods in comments for some time.

The copyright header template at:

    https://golang.org/doc/contribute.html#copyright

also uses a single space.

Make them all consistent.

Change-Id: Icc26c6b8495c3820da6b171ca96a74701b4a01b0
Reviewed-on: https://go-review.googlesource.com/20111
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2016-03-01 23:34:33 +00:00
Russ Cox 04d732b4c2 build: shorten a few packages with long tests
Takes 3% off my all.bash run time.

For #10571.

Change-Id: I8f00f523d6919e87182d35722a669b0b96b8218b
Reviewed-on: https://go-review.googlesource.com/18087
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2015-12-29 15:46:44 +00:00
David Chase 38255cbd1b math/rand: improve uniformity of rand.Float64,Float32
Replaced code that substituted 0 for rounded-up 1 with
code to try again.  This has minimal effect on the existing
stream of random numbers, but restores uniformity.

Fixes #12290.

Change-Id: Ib68f0b0a4a173339bcd0274cc16509f7b0977de8
Reviewed-on: https://go-review.googlesource.com/17670
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2015-12-11 15:17:42 +00:00
Jingguo Yao fb01ad21c2 math/rand: add a comment for the i=0 iteration
Fixes #13215

Change-Id: I126117d42e7c1e69cbc7fad0760e225b03ed15bd
Reviewed-on: https://go-review.googlesource.com/16852
Reviewed-by: Keith Randall <khr@golang.org>
2015-11-15 08:21:29 +00:00