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Inflate fast NEON optimization #345

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Inflate fast NEON optimization #345

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Commits on Apr 5, 2018

  1. Porting inflate using wider loads and stores 

    In inflate_fast() the output pointer always has plenty of room to write. This
means that so long as the target is capable, wide un-aligned loads and stores
can be used to transfer several bytes at once. When the reference distance is
too short simply unroll the data a little to increase the distance.

For reference, please see:
https://chromium.googlesource.com/chromium/src/+/78104f4d73e3bbb4155fa804d00ed66682180556
ps: this is still missing the fix for inflate_back corner case.

Change-Id: I5216424ab584e069b77ddf04000a313d5ca99839
    Adenilson Cavalcanti committed Apr 5, 2018
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  2. Port Fix InflateBack corner case 

    This handles the case where a zlib user could rely on InflateBack
API to decompress content.

The NEON optimization assumes that it can perform wide stores, sometimes
overwriting data on the output pointer (but never overflowing the buffer
end as it has enough room for the write).

For infback there is no such guarantees (i.e. no extra wiggle room),
which can result in illegal operations. This patch fixes the potential
issue by falling back to the non-optimized code for such cases.

Also it adds some comments about the entry assumptions in inflate and
writes out a defined value at the write buffer to identify where
the real data has ended (helpful while debugging).

For reference, please see:
https://chromium.googlesource.com/chromium/src/+/0bb11040792edc5b28fcb710fc4c01fedd98c97c

Change-Id: Iffbda9eb5e08a661aa15c6e3d1c59b678cc23b2c
    Adenilson Cavalcanti committed Apr 5, 2018
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