This modifies the normalize function of the internal field value to
both optimize it and address an issue where the reduction could
lead to an incorrect result with a small range of values. It also adds
tests to ensure the behavior is correct.
The following benchmark shows the relative speedups as a result of the
optimization on my system. In particular, the changes result in
approximately a 14% speedup in Normalize, which ultimately translates to
a 2% speedup in signature verifies.
benchmark old ns/op new ns/op delta
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BenchmarkAddJacobian 1364 1289 -5.50%
BenchmarkAddJacobianNotZOne 3150 3091 -1.87%
BenchmarkScalarBaseMult 134117 132816 -0.97%
BenchmarkScalarBaseMultLarge 135067 132966 -1.56%
BenchmarkScalarMult 411218 402217 -2.19%
BenchmarkSigVerify 671585 657833 -2.05%
BenchmarkFieldNormalize 36.0 31.0 -13.89%
Putting the test code in the same package makes it easier for forks
since they don't have to change the import paths as much and it also
gets rid of the need for internal_test.go to bridge.
Also, remove the exception from the lint checks about returning the
unexported type since it is no longer required.
This adds new tests to the TestNormalize, TestMul, TestAdd2 functions
which trigger an issue with modular reduction that was fixed in the
prevous commit to prevent regressions.
