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s2: Improve coding for long, close matches #613

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merged 2 commits into from
Jun 2, 2022
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@klauspost klauspost commented Jun 2, 2022

Use one less byte when emitting copies that are >64 and offset <2048

Before we emit 60 bytes (3 byte encoding) and remaining as repeat. Now we emit 8 bytes (2 byte encoding) + repeat. Repeat may in rare cases eat back the saved byte, but it is never worse.

before -> after:

consensus.db.10gb: 4244773384 -> 4228831520
nyc-taxi-data-10M.csv: 779098746 -> 776295996
github-june-2days-2019.json: 832855431 -> 831242779
github-ranks-backup.bin: 554428594 -> 554340949

Typically 0.1% improvement.

Use one less byte when emitting copies that are >64 and offset <2048

consensus.db.10gb: 4244773384 -> 4228831520
nyc-taxi-data-10M.csv: 779098746 -> 776295996
github-june-2days-2019.json: 832855431 -> 831242779
github-ranks-backup.bin: 554428594 -> 554340949
@klauspost klauspost merged commit 72cae76 into master Jun 2, 2022
@klauspost klauspost deleted the s2-improve-coding branch June 2, 2022 17:43
@klauspost klauspost changed the title s2: Improve coding for close matches s2: Improve coding for long, close matches Jun 3, 2022
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