strconv: faster FormatFloat(x, *, -1, 64) using Grisu3 algorithm.
The implementation is similar to the one from the double-conversion
library used in the Chrome V8 engine.
old ns/op new ns/op speedup
BenchmarkAppendFloatDecimal 591 480 1.2x
BenchmarkAppendFloat 2956 486 6.1x
BenchmarkAppendFloatExp 10622 503 21.1x
BenchmarkAppendFloatNegExp 40343 483 83.5x
BenchmarkAppendFloatBig 2798 664 4.2x
See F. Loitsch, ``Printing Floating-Point Numbers Quickly and
Accurately with Integers'', Proceedings of the ACM, 2010.
R=rsc
CC=golang-dev, remy
https://golang.org/cl/
5502079