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Joe Tsai e20106ac00 time: optimize FixedZone by caching unnamed zones by the hour
FixedZone is transitively called by Time.UnmarshalJSON or Time.UnmarshalText
for any RFC 3339 timestamp that is not in UTC.
This function is relatively slow since it allocates 3 times.

Given that RFC 3339 never has a zone name and most offsets are by the hour,
we can cache unnamed zones on hour offsets.
Caching a Location should be safe since it has no exported fields or methods
that can mutate the Location. It is functionally immutable.

The only way to observe that the Location was cached is either
by pointer comparison or by shallow copying the struct value.
Neither operation seems sensible to do with a *time.Location.

Performance:

	name           old time/op  new time/op  delta
	UnmarshalText  268ns ± 2%   182ns ± 1%  -32.01%  (p=0.000 n=10+10)

Change-Id: Iab5432f34bdbb485512bb8b5464e076c03fd106f
Reviewed-on: https://go-review.googlesource.com/c/go/+/425116
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
Auto-Submit: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Ian Lance Taylor <iant@google.com>
2022-09-08 21:18:53 +00:00
.github .github: update issue label for pkgsite-removal 2022-09-07 16:00:20 +00:00
api debug/elf: define additional PPC64 ELFv2 relocations 2022-09-08 13:31:46 +00:00
doc spec: describe slice-to-array conversions 2022-09-08 16:37:47 +00:00
lib/time lib/time, time/tzdata: update to 2022b 2022-08-11 20:03:19 +00:00
misc misc: use strings.Builder 2022-09-06 15:44:25 +00:00
src time: optimize FixedZone by caching unnamed zones by the hour 2022-09-08 21:18:53 +00:00
test go/types, types2: implement slice-to-array conversions 2022-09-08 15:55:44 +00:00
.gitattributes all: treat all files as binary, but check in .bat with CRLF 2020-06-08 15:31:43 +00:00
.gitignore internal/buildcfg: move build configuration out of cmd/internal/objabi 2021-04-16 19:20:53 +00:00
codereview.cfg codereview.cfg: add codereview.cfg for master branch 2021-02-19 18:44:53 +00:00
CONTRIBUTING.md all: restore changes from faulty merge/revert 2018-02-12 20:13:59 +00:00
LICENSE doc: revert copyright date to 2009 2016-06-01 22:40:04 +00:00
PATENTS LICENSE: separate, change PATENTS text 2010-12-06 16:31:59 -05:00
README.md README.md: update wiki link 2022-04-26 16:21:18 +00:00
SECURITY.md SECURITY.md: replace golang.org with go.dev 2022-04-26 19:59:47 +00:00

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