| * common/math: optimize PaddedBigBytes, use it more
name              old time/op    new time/op    delta
PaddedBigBytes-8    71.1ns ± 5%    46.1ns ± 1%  -35.15%  (p=0.000 n=20+19)
name              old alloc/op   new alloc/op   delta
PaddedBigBytes-8     48.0B ± 0%     32.0B ± 0%  -33.33%  (p=0.000 n=20+20)
* all: unify big.Int zero checks
Various checks were in use. This commit replaces them all with Int.Sign,
which is cheaper and less code.
eg templates:
    func before(x *big.Int) bool { return x.BitLen() == 0 }
    func after(x *big.Int) bool  { return x.Sign() == 0 }
    func before(x *big.Int) bool { return x.BitLen() > 0 }
    func after(x *big.Int) bool  { return x.Sign() != 0 }
    func before(x *big.Int) int { return x.Cmp(common.Big0) }
    func after(x *big.Int) int  { return x.Sign() }
* common/math, crypto/secp256k1: make ReadBits public in package math | ||
|---|---|---|
| .. | ||
| big_test.go | ||
| big.go | ||
| integer_test.go | ||
| integer.go | ||