encoding/hex: don't overallocate memory in DecodeString

[mateusz834]

Now as []byte(string) doesn't always cause heap allocation (CL 520599, #2205)
we can make DecodeString simpler and more performant, by not allocating
x2 the required memory.

goos: linux
goarch: amd64
pkg: encoding/hex
cpu: AMD Ryzen 5 4600G with Radeon Graphics
│ beforehex │ afterhex │
│ sec/op │ sec/op vs base │
DecodeString/256-12 197.9n ± 1% 172.2n ± 1% -13.01% (p=0.000 n=10)
DecodeString/1024-12 684.9n ± 1% 598.5n ± 1% -12.61% (p=0.000 n=10)
DecodeString/4096-12 2.764µ ± 0% 2.343µ ± 1% -15.23% (p=0.000 n=10)
DecodeString/16384-12 10.774µ ± 1% 9.348µ ± 1% -13.23% (p=0.000 n=10)
geomean 1.417µ 1.226µ -13.53%

                  │  beforehex   │               afterhex               │
                  │     B/s      │     B/s       vs base                │

DecodeString/256-12 1.205Gi ± 1% 1.385Gi ± 1% +14.94% (p=0.000 n=10)
DecodeString/1024-12 1.393Gi ± 1% 1.593Gi ± 1% +14.42% (p=0.000 n=10)
DecodeString/4096-12 1.380Gi ± 0% 1.628Gi ± 1% +17.97% (p=0.000 n=10)
DecodeString/16384-12 1.416Gi ± 1% 1.632Gi ± 1% +15.25% (p=0.000 n=10)
geomean 1.346Gi 1.556Gi +15.64%

                  │   beforehex   │               afterhex               │
                  │     B/op      │     B/op      vs base                │

DecodeString/256-12 256.0 ± 0% 128.0 ± 0% -50.00% (p=0.000 n=10)
DecodeString/1024-12 1024.0 ± 0% 512.0 ± 0% -50.00% (p=0.000 n=10)
DecodeString/4096-12 4.000Ki ± 0% 2.000Ki ± 0% -50.00% (p=0.000 n=10)
DecodeString/16384-12 16.000Ki ± 0% 8.000Ki ± 0% -50.00% (p=0.000 n=10)
geomean 2.000Ki 1.000Ki -50.00%

                  │ beforehex  │              afterhex               │
                  │ allocs/op  │ allocs/op   vs base                 │

DecodeString/256-12 1.000 ± 0% 1.000 ± 0% ~ (p=1.000 n=10) ¹
DecodeString/1024-12 1.000 ± 0% 1.000 ± 0% ~ (p=1.000 n=10) ¹
DecodeString/4096-12 1.000 ± 0% 1.000 ± 0% ~ (p=1.000 n=10) ¹
DecodeString/16384-12 1.000 ± 0% 1.000 ± 0% ~ (p=1.000 n=10) ¹
geomean 1.000 1.000 +0.00%

[gopherbot]

This PR (HEAD: a72fdb1) has been imported to Gerrit for code review.

Please visit Gerrit at https://go-review.googlesource.com/c/go/+/584118.

Important tips:

• Don't comment on this PR. All discussion takes place in Gerrit.
• You need a Gmail or other Google account to log in to Gerrit.
• To change your code in response to feedback:
  • Push a new commit to the branch used by your GitHub PR.
  • A new "patch set" will then appear in Gerrit.
  • Respond to each comment by marking as Done in Gerrit if implemented as suggested. You can alternatively write a reply.
  • Critical: you must click the blue Reply button near the top to publish your Gerrit responses.
  • Multiple commits in the PR will be squashed by GerritBot.
• The title and description of the GitHub PR are used to construct the final commit message.
  • Edit these as needed via the GitHub web interface (not via Gerrit or git).
  • You should word wrap the PR description at ~76 characters unless you need longer lines (e.g., for tables or URLs).
• See the Sending a change via GitHub and Reviews sections of the Contribution Guide as well as the FAQ for details.

[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Mateusz Poliwczak:

Patch Set 1: Commit-Queue+1

(1 comment)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Go LUCI:

Patch Set 1:

Dry run: CV is trying the patch.

Bot data: {"action":"start","triggered_at":"2024-05-08T17:28:02Z","revision":"e9fa3863eea88f9b24ba130bb334761c7d959a1b"}

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Mateusz Poliwczak:

Patch Set 1: -Commit-Queue

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Go LUCI:

Patch Set 1:

This CL has passed the run

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Go LUCI:

Patch Set 1: LUCI-TryBot-Result+1

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

This PR (HEAD: aeedf3f) has been imported to Gerrit for code review.

Please visit Gerrit at https://go-review.googlesource.com/c/go/+/584118.

Important tips:

• Don't comment on this PR. All discussion takes place in Gerrit.
• You need a Gmail or other Google account to log in to Gerrit.
• To change your code in response to feedback:
  • Push a new commit to the branch used by your GitHub PR.
  • A new "patch set" will then appear in Gerrit.
  • Respond to each comment by marking as Done in Gerrit if implemented as suggested. You can alternatively write a reply.
  • Critical: you must click the blue Reply button near the top to publish your Gerrit responses.
  • Multiple commits in the PR will be squashed by GerritBot.
• The title and description of the GitHub PR are used to construct the final commit message.
  • Edit these as needed via the GitHub web interface (not via Gerrit or git).
  • You should word wrap the PR description at ~76 characters unless you need longer lines (e.g., for tables or URLs).
• See the Sending a change via GitHub and Reviews sections of the Contribution Guide as well as the FAQ for details.

[gopherbot]

Message from Ian Lance Taylor:

Patch Set 1: Auto-Submit+1 Code-Review+2 Commit-Queue+1

(1 comment)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Go LUCI:

Patch Set 1:

Dry run: CV is trying the patch.

Bot data: {"action":"start","triggered_at":"2024-05-08T18:23:41Z","revision":"e9fa3863eea88f9b24ba130bb334761c7d959a1b"}

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Go LUCI:

Patch Set 1: LUCI-TryBot-Result-1

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Mateusz Poliwczak:

Patch Set 2: Commit-Queue+1

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Go LUCI:

Patch Set 2:

Dry run: CV is trying the patch.

Bot data: {"action":"start","triggered_at":"2024-05-08T18:27:05Z","revision":"e83b5d425ac3b0652f1c187425de4d1689bea7dd"}

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Ian Lance Taylor:

Patch Set 2: Auto-Submit+1 Code-Review+2 Commit-Queue+1

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Ian Lance Taylor:

Patch Set 2: -Commit-Queue

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Mateusz Poliwczak:

Patch Set 2: -Commit-Queue

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Go LUCI:

Patch Set 2:

This CL has passed the run

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Go LUCI:

Patch Set 2: LUCI-TryBot-Result+1

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/584118.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

This PR is being closed because golang.org/cl/584118 has been merged.