[Bug 1742941] Re: zlib: improve crc32 performance on P8

[Launchpad Bug Tracker]

This bug was fixed in the package zlib - 1:1.2.11.dfsg-2ubuntu1

---------------
zlib (1:1.2.11.dfsg-2ubuntu1) focal; urgency=medium

  * Merge with Debian; remaining changes:
    - Build x32 packages
    - debian/zlib-core.symbols: Drop dfsg suffix from version
    - Add watch file, with GPG tarball checking, and version mangling
    - Drop unused patches
    - Cherry-pick Permit-a-deflateParams-parameter-change-asap.patch:
      (LP: #1692870)
    - Cherrypick PR#410 to enable hardware-accelerated deflate.
    - Copmile with DFLTCC enabled on s390x. LP: #1823157
    - Improve crc32 performance on P8, proposed upstream patch. LP: #1742941.

zlib (1:1.2.11.dfsg-2) unstable; urgency=low

  * Acknowledge previous NMUs (closes: #949388).
  * Remove zlib1g-dbg in favour of dbgsym (closes: #497831, #926161).
  * Rename stage1 to nobiarch, patch no longer applies due to
    uncoordinated NMUs (closes: #892762).
  * Debhelper has renamed -s to -a.
  * Policy 4.5.0 (no changes).

zlib (1:1.2.11.dfsg-1.2ubuntu1) focal; urgency=medium

  * Merge with Debian; remaining changes:
    - Build x32 packages
    - debian/zlib-core.symbols: Drop dfsg suffix from version
    - Add watch file, with GPG tarball checking, and version mangling
    - Drop unused patches
    - Cherry-pick Permit-a-deflateParams-parameter-change-asap.patch:
      (LP: #1692870)
    - Cherrypick PR#410 to enable hardware-accelerated deflate.
    - Copmile with DFLTCC enabled on s390x. LP: #1823157
  * Improve crc32 performance on P8, proposed upstream patch. LP: #1742941.

zlib (1:1.2.11.dfsg-1.2) unstable; urgency=medium

  * Non-maintainer upload.
  * Fix ftbfs on mips64el caused by the previous NMU by
    remove it from 32-ARCHS to keep NMU minial.

zlib (1:1.2.11.dfsg-1.1) unstable; urgency=medium

  * Non-maintainer upload.
  * Enable lib64 for mipsn32 mipsn32el mipsr6 mipsr6el mipsn32r6 mipsn32r6el x32
    help to add binutils-host64 for 32bit architectures (Closes: 949388)
  * Remove outdated binutils version requirement for mips/mipsel.

 -- Matthias Klose <doko at ubuntu.com>  Tue, 25 Feb 2020 16:59:52 +0100

** Changed in: zlib (Ubuntu)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1742941

Title:
  zlib: improve  crc32 performance on P8

Status in The Ubuntu-power-systems project:
  Fix Committed
Status in zlib package in Ubuntu:
  Fix Released

Bug description:
  Calculate the checksum of data that is 16 byte aligned and a multiple
  of  16 bytes.

  The first step is to reduce it to 1024 bits. We do this in 8 parallel
   chunks in order to mask the latency of the vpmsum instructions. If we
   have more than 32 kB of data to checksum we repeat this step multiple
   times, passing in the previous 1024 bits.

   The next step is to reduce the 1024 bits to 64 bits. This step adds
   32 bits of 0s to the end - this matches what a CRC does. We just
   calculate constants that land the data in this 32 bits.

   We then use fixed point Barrett reduction to compute a mod n over GF(2)
   for n = CRC using POWER8 instructions. We use x = 32.

   http://en.wikipedia.org/wiki/Barrett_reduction

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