zstd: Improve best compression's match selection #705
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The best encoder selects matches based on the criterion a.est+(a.s-b.s)*bitsPerByte>>10 < b.est+(b.s-a.s)*bitsPerByte>>10 If this were computed on the reals, it would be equivalent to a.est < b.est, so the added terms only capture round-off error (this is also why CSE doesn't eliminate them). Changing the formula to a.est-b.est+(a.s-b.s)*bitsPerByte>>10 < 0 captures the intention better, I think, and improves compression: enwik9 260989017 259699309 -0.4942% silesia/dickens 3233958 3222189 -0.3639% silesia/mozilla 16980973 16912341 -0.4042% silesia/mr 3505223 3505553 0.0094% silesia/nci 2313702 2289871 -1.0300% silesia/ooffice 2915199 2896410 -0.6445% silesia/osdb 3364752 3390871 0.7763% silesia/reymont 1658404 1656006 -0.1446% silesia/samba 4330660 4326783 -0.0895% silesia/sao 5399736 5416932 0.3185% silesia/webster 9987784 9966351 -0.2146% silesia/xml 542081 538378 -0.6831% silesia/x-ray 5756210 5733061 -0.4022% ... as well as throughput: name old speed new speed delta Encoder_EncodeAllSimple/best-8 12.1MB/s ± 1% 12.2MB/s ± 1% +1.17% (p=0.000 n=18+20) Encoder_EncodeAllSimple4K/best-8 10.4MB/s ± 1% 10.5MB/s ± 1% +0.82% (p=0.000 n=20+20)
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…7575) This PR contains the following updates: | Package | Type | Update | Change | |---|---|---|---| | [github.com/klauspost/compress](https://togithub.com/klauspost/compress) | indirect | patch | `v1.15.11` -> `v1.15.15` | --- ### Release Notes <details> <summary>klauspost/compress</summary> ### [`v1.15.15`](https://togithub.com/klauspost/compress/releases/tag/v1.15.15) [Compare Source](https://togithub.com/klauspost/compress/compare/v1.15.14...v1.15.15) ##### What's Changed - zstd: Add delta encoding support by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#728 - huff0: Reduce bounds checking by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#734 - huff0: Assembler improvements by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#736 - deflate: Improve level 7-9 by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#739 - gzhttp: Add SuffixETag() and DropETag() options to prevent ETag collisions on compressed responses by [@​willbicks](https://togithub.com/willbicks) in [klauspost/compress#740 - zstd: Don't allocate dataStorage when using byteBuf by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#741 - huff0: Speed up compression of short blocks by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#744 - zstd: Handle dicts by pointer, always by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#743 - fse: Optimize compression by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#745 - Retract v1.14.1-v.1.14.3 by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#742 ##### New Contributors - [@​willbicks](https://togithub.com/willbicks) made their first contribution in [klauspost/compress#740 **Full Changelog**: klauspost/compress@v1.15.14...v1.15.15 ### [`v1.15.14`](https://togithub.com/klauspost/compress/releases/tag/v1.15.14) [Compare Source](https://togithub.com/klauspost/compress/compare/v1.15.13...v1.15.14) #### What's Changed - flate: Improve speed in big stateless blocks. by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#718 - zstd: Trigger BCE by switching on lengths by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#716 - zstd: Shave some instructions off the amd64 asm by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#720 - export NoGzipResponseWriter for custom ResponseWriter wrappers by [@​harshavardhana](https://togithub.com/harshavardhana) in [klauspost/compress#722 - s2: Add example for indexing and existing stream by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#723 - tests: Tweak fuzz tests by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#719 #### New Contributors - [@​harshavardhana](https://togithub.com/harshavardhana) made their first contribution in [klauspost/compress#722 **Full Changelog**: klauspost/compress@v1.15.13...v1.15.14 ### [`v1.15.13`](https://togithub.com/klauspost/compress/releases/tag/v1.15.13) [Compare Source](https://togithub.com/klauspost/compress/compare/v1.15.12...v1.15.13) #### What's Changed - zstd: Add MaxEncodedSize to encoder by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#691 - zstd: Improve "best" end search by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#693 - zstd: Replace bytes.Equal with smaller comparisons by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#695 - zstd: Faster CRC checking/skipping by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#696 - zstd: Rewrite matchLen to make it inlineable by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#701 - zstd: Write table clearing in a way that the compiler recognizes by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#702 - zstd: Use individual reset threshold by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#703 - huff0: Check for zeros earlier in Scratch.countSimple by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#704 - zstd: Improve best compression's match selection by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#705 - zstd: Select best match using selection trees by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#706 - zstd: sync xxhash with final accepted patch upstream by [@​lizthegrey](https://togithub.com/lizthegrey) in [klauspost/compress#707 - zstd: Import xxhash v2.2.0 by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#708 **Full Changelog**: klauspost/compress@v1.15.12...v1.15.13 ### [`v1.15.12`](https://togithub.com/klauspost/compress/releases/tag/v1.15.12) [Compare Source](https://togithub.com/klauspost/compress/compare/v1.15.11...v1.15.12) ##### What's Changed - zstd: Tweak decoder allocs. by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#680 - gzhttp: Always delete `HeaderNoCompression` by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#683 **Full Changelog**: klauspost/compress@v1.15.11...v1.15.12 </details> --- ### Configuration 📅 **Schedule**: Branch creation - "before 3am on the first day of the month" (UTC), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box --- This PR has been generated by [Renovate Bot](https://togithub.com/renovatebot/renovate). <!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzNC4xMDkuMSIsInVwZGF0ZWRJblZlciI6IjM0LjEwOS4xIn0=-->
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This PR contains the following updates: | Package | Type | Update | Change | |---|---|---|---| | [github.com/klauspost/compress](https://togithub.com/klauspost/compress) | indirect | minor | `v1.15.11` -> `v1.16.0` | --- ### ⚠ Dependency Lookup Warnings ⚠ Warnings were logged while processing this repo. Please check the Dependency Dashboard for more information. --- ### Release Notes <details> <summary>klauspost/compress</summary> ### [`v1.16.0`](https://togithub.com/klauspost/compress/releases/tag/v1.16.0) [Compare Source](https://togithub.com/klauspost/compress/compare/v1.15.15...v1.16.0) #### What's Changed - s2: Add Dictionary support by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#685 - s2: Add Compression Size Estimate by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#752 - s2: Add support for custom stream encoder by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#755 - s2: Add LZ4 block converter by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#748 - s2: Support io.ReaderAt in ReadSeeker by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#747 - s2c/s2sx: Use concurrent decoding by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#746 - tests: Upgrade to Go 1.20 by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#749 - Update all (command) dependencies by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#758 **Full Changelog**: klauspost/compress@v1.15.15...v1.16.0 ### [`v1.15.15`](https://togithub.com/klauspost/compress/releases/tag/v1.15.15) [Compare Source](https://togithub.com/klauspost/compress/compare/v1.15.14...v1.15.15) #### What's Changed - zstd: Add delta encoding support by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#728 - huff0: Reduce bounds checking by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#734 - huff0: Assembler improvements by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#736 - deflate: Improve level 7-9 by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#739 - gzhttp: Add SuffixETag() and DropETag() options to prevent ETag collisions on compressed responses by [@​willbicks](https://togithub.com/willbicks) in [klauspost/compress#740 - zstd: Don't allocate dataStorage when using byteBuf by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#741 - huff0: Speed up compression of short blocks by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#744 - zstd: Handle dicts by pointer, always by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#743 - fse: Optimize compression by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#745 - Retract v1.14.1-v.1.14.3 by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#742 #### New Contributors - [@​willbicks](https://togithub.com/willbicks) made their first contribution in [klauspost/compress#740 **Full Changelog**: klauspost/compress@v1.15.14...v1.15.15 ### [`v1.15.14`](https://togithub.com/klauspost/compress/releases/tag/v1.15.14) [Compare Source](https://togithub.com/klauspost/compress/compare/v1.15.13...v1.15.14) #### What's Changed - flate: Improve speed in big stateless blocks. by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#718 - zstd: Trigger BCE by switching on lengths by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#716 - zstd: Shave some instructions off the amd64 asm by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#720 - export NoGzipResponseWriter for custom ResponseWriter wrappers by [@​harshavardhana](https://togithub.com/harshavardhana) in [klauspost/compress#722 - s2: Add example for indexing and existing stream by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#723 - tests: Tweak fuzz tests by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#719 #### New Contributors - [@​harshavardhana](https://togithub.com/harshavardhana) made their first contribution in [klauspost/compress#722 **Full Changelog**: klauspost/compress@v1.15.13...v1.15.14 ### [`v1.15.13`](https://togithub.com/klauspost/compress/releases/tag/v1.15.13) [Compare Source](https://togithub.com/klauspost/compress/compare/v1.15.12...v1.15.13) #### What's Changed - zstd: Add MaxEncodedSize to encoder by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#691 - zstd: Improve "best" end search by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#693 - zstd: Replace bytes.Equal with smaller comparisons by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#695 - zstd: Faster CRC checking/skipping by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#696 - zstd: Rewrite matchLen to make it inlineable by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#701 - zstd: Write table clearing in a way that the compiler recognizes by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#702 - zstd: Use individual reset threshold by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#703 - huff0: Check for zeros earlier in Scratch.countSimple by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#704 - zstd: Improve best compression's match selection by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#705 - zstd: Select best match using selection trees by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#706 - zstd: sync xxhash with final accepted patch upstream by [@​lizthegrey](https://togithub.com/lizthegrey) in [klauspost/compress#707 - zstd: Import xxhash v2.2.0 by [@​greatroar](https://togithub.com/greatroar) in [klauspost/compress#708 **Full Changelog**: klauspost/compress@v1.15.12...v1.15.13 ### [`v1.15.12`](https://togithub.com/klauspost/compress/releases/tag/v1.15.12) [Compare Source](https://togithub.com/klauspost/compress/compare/v1.15.11...v1.15.12) #### What's Changed - zstd: Tweak decoder allocs. by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#680 - gzhttp: Always delete `HeaderNoCompression` by [@​klauspost](https://togithub.com/klauspost) in [klauspost/compress#683 **Full Changelog**: klauspost/compress@v1.15.11...v1.15.12 </details> --- ### Configuration 📅 **Schedule**: Branch creation - "before 3am on the first day of the month" (UTC), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box --- This PR has been generated by [Renovate Bot](https://togithub.com/renovatebot/renovate). <!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzNC4xMDkuMSIsInVwZGF0ZWRJblZlciI6IjM0LjE1NC4wIn0=-->
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name old speed new speed delta Encoder_EncodeAllSimple/best-8 14.8MB/s ± 3% 20.7MB/s ± 3% +39.53% (p=0.000 n=17+19) Encoder_EncodeAllSimple4K/best-8 11.8MB/s ± 1% 19.2MB/s ± 6% +62.17% (p=0.000 n=20+20) name old alloc/op new alloc/op delta Encoder_EncodeAllSimple/best-8 14.0B ± 0% 10.2B ± 8% -27.07% (p=0.000 n=16+19) Encoder_EncodeAllSimple4K/best-8 1.00B ± 0% 0.00B -100.00% (p=0.000 n=20+19) Also, compressing enwik9 takes 6.375% less wall clock time. Output from silesia corpus and enwik9 is about .05% bigger, due to the different order in which comparisons are done: dickens 3222189 3220994 (× 0.99963) enwik9 259699309 259846164 (× 1.00057) mozilla 16912341 16912437 (× 1.00001) mr 3505553 3502823 (× 0.99922) nci 2289871 2306320 (× 1.00718) ooffice 2896410 2896907 (× 1.00017) osdb 3390871 3390548 (× 0.99990) reymont 1656006 1657380 (× 1.00083) samba 4326783 4329898 (× 1.00072) sao 5416932 5416648 (× 0.99995) webster 9966351 9972808 (× 1.00065) xml 538378 542277 (× 1.00724) x-ray 5733061 5733121 (× 1.00001) total 319554055 319728325 (× 1.00055) This is still smaller than before klauspost#705.
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name old speed new speed delta Encoder_EncodeAllSimple/best-8 14.8MB/s ± 3% 20.7MB/s ± 3% +39.53% (p=0.000 n=17+19) Encoder_EncodeAllSimple4K/best-8 11.8MB/s ± 1% 19.2MB/s ± 6% +62.17% (p=0.000 n=20+20) name old alloc/op new alloc/op delta Encoder_EncodeAllSimple/best-8 14.0B ± 0% 10.2B ± 8% -27.07% (p=0.000 n=16+19) Encoder_EncodeAllSimple4K/best-8 1.00B ± 0% 0.00B -100.00% (p=0.000 n=20+19) Also, compressing enwik9 takes 6.375% less wall clock time. Output from silesia corpus and enwik9 is about .05% bigger, due to the different order in which comparisons are done: dickens 3222189 3220994 (× 0.99963) enwik9 259699309 259846164 (× 1.00057) mozilla 16912341 16912437 (× 1.00001) mr 3505553 3502823 (× 0.99922) nci 2289871 2306320 (× 1.00718) ooffice 2896410 2896907 (× 1.00017) osdb 3390871 3390548 (× 0.99990) reymont 1656006 1657380 (× 1.00083) samba 4326783 4329898 (× 1.00072) sao 5416932 5416648 (× 0.99995) webster 9966351 9972808 (× 1.00065) xml 538378 542277 (× 1.00724) x-ray 5733061 5733121 (× 1.00001) total 319554055 319728325 (× 1.00055) This is still smaller than before #705.
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The best encoder selects matches based on the criterion
If this were computed on the reals, it would be equivalent to a.est < b.est, so the added terms only capture round-off error (this is also why CSE doesn't eliminate them).
Changing the formula to
captures the intention better, I think, and improves compression:
... as well as throughput: