shares: powersOf2 test should put less expensive comparison before AND and SUBTRACTION

[odeke-em]

Summary of Bug

If we examine this code to determine if a value is a power of 2

go-square/shares/powers_of_two.go

Line 43 in 4135f35

return input&(input-1) == 0 && input != 0

notice that the test for if a value is 0 comes after the more expensive subtraction after an AND but also we need to simply check that the value is greater than 0 because that test fails anyways for negative powers of 2 for example -4, -8, -2 etc

Suggestion

return input > 0 && input&(input-1) == 0

/cc @elias-orijtech

Version

4135f35

Steps to Reproduce

Please follow the steps that I reported

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned

[odeke-em]

Actually nevermind, it is a non-issue.