Dave Collins 1238b7e55a btcec: Optimize and correct normalize. ...

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
--------------------------------------------------------------------
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%

2017-06-07 20:43:36 -05:00

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