golang/go

math/big: optimize amd64 asm shlVU and shrVU for shift==0 case

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#31,097 opened on Mar 28, 2019

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Description

When shift == 0, shlVU and shrVU reduce to a memcopy. When z.ptr == x.ptr, it further reduces to a no-op. The pure Go implementation has these optimizations, as of https://go-review.googlesource.com/c/go/+/164967. The arm64 implementation has one of them (see https://github.com/golang/go/issues/31084#issuecomment-477406354). We should add both to the amd64 implementation.

cc @griesemer

Contributor guide

Research direction
Inspect the existing amd64 assembly for shlVU and shrVU in the Go source code, and add the shift==0 optimization. Look at the arm64 implementation and the pure Go implementation for reference.
Tech stack
go
Domain
backend
Issue type
Performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Goamd64 assembly
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60