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Optimize software gcm_mult() routines on strictly-aligned systems #9489

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Optimize software gcm_mult() routines on strictly-aligned systems #9489

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@rsaxvc rsaxvc commented Aug 20, 2024

Description

Micro-optimize gcm_mult_largetable() and gcm_mult_smalltable(), tuning for 32-bit systems and restoring performance on strictly-aligned systems lost as part of #8716 . Some improvement in gcm_mult_smalltable() should also help systems with unaligned accesses as well.

These are cycles measured on an Xtensa core without unaligned accesses.

Implementation Cycles/Block Cycles/Byte
Old gcm_mult() (pre-#8716) 1214 75.88
gcm_mult_smalltable() 4139 258.7
gcm_mult_smalltable() proposed 936 58.5
gcm_mult_largetable() 2168 135.5
gcm_mult_largetable() proposed 599 37.4

PR checklist

  • changelog provided
  • tests covered by existing test cases

@rsaxvc
Optimize software gcm_mult() routines on strictly-aligned systems
008ffcc 
Remove type-punning from the inner loop, and do most operations
on uint64_t instead.

Pre-shift last4[] to take advantage of free <<32 on 32-bit machines.

Fixes Mbed-TLS#9476

Signed-off-by: Richard Allen <[email protected]>
@rsaxvc rsaxvc marked this pull request as ready for review August 20, 2024 12:30
@minosgalanakis minosgalanakis added needs-review Every commit must be reviewed by at least two team members, needs-backports Backports are missing or are pending review and approval. component-platform Portability layer and build scripts needs-ci Needs to pass CI tests needs-reviewer This PR needs someone to pick it up for review size-s Estimated task size: small (~2d) labels Aug 21, 2024
@gilles-peskine-arm gilles-peskine-arm added component-crypto Crypto primitives and low-level interfaces priority-medium Medium priority - this can be reviewed as time permits and removed component-platform Portability layer and build scripts labels Oct 28, 2024
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component-crypto Crypto primitives and low-level interfaces needs-backports Backports are missing or are pending review and approval. needs-ci Needs to pass CI tests needs-review Every commit must be reviewed by at least two team members, needs-reviewer This PR needs someone to pick it up for review priority-medium Medium priority - this can be reviewed as time permits size-s Estimated task size: small (~2d)
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@rsaxvc @gilles-peskine-arm @minosgalanakis