Module lexical::ftoa

Fast lexical float-to-string conversion routines.

The optimized routines are adapted from Andrea Samoljuk's fpconv library, which is available here.

The radix-generic algorithm is adapted from the V8 codebase, and may be found here.

The following benchmarks were run on an "Intel(R) Core(TM) i7-6560U CPU @ 2.20GHz" CPU, on Fedora 28, Linux kernel version 4.18.16-200 (x86-64), using the lexical formatter, dtoa::write() or x.to_string(), avoiding any inefficiencies in Rust string parsing for format!(...) or write!() macros. The code was compiled with LTO and at an optimization level of 3.

The benchmarks with std were compiled using "rustc 1.29.2 (17a9dc751 2018-10-05", and the no_std benchmarks were compiled using "rustc 1.31.0-nightly (46880f41b 2018-10-15)".

The benchmark code may be found benches/ftoa.rs.

Benchmarks

Type	lexical (ns/iter)	to_string (ns/iter)	Relative Increase
f32	1,221,025	2,711,290	2.22x
f64	1,248,397	3,558,305	2.85x

Raw Benchmarks

test f32_dtoa      ... bench:   1,301,173 ns/iter (+/- 45,283)
test f32_lexical   ... bench:   1,221,025 ns/iter (+/- 42,428)
test f32_to_string ... bench:   2,711,290 ns/iter (+/- 75,376)
test f64_dtoa      ... bench:   1,462,523 ns/iter (+/- 103,974)
test f64_lexical   ... bench:   1,248,397 ns/iter (+/- 41,952)
test f64_to_string ... bench:   3,558,305 ns/iter (+/- 103,945)

Raw Benchmarks (no_std)

test f32_dtoa      ... bench:   1,727,839 ns/iter (+/- 76,330)
test f32_lexical   ... bench:   1,461,892 ns/iter (+/- 95,811)
test f32_to_string ... bench:   3,687,219 ns/iter (+/- 313,885)
test f64_dtoa      ... bench:   1,927,419 ns/iter (+/- 122,000)
test f64_lexical   ... bench:   1,505,955 ns/iter (+/- 87,548)
test f64_to_string ... bench:   4,774,595 ns/iter (+/- 244,214)

Functions

exponent_notation_char	Get the exponent notation character.
f32toa_unsafe⚠	Unsafe, C-like exporter for float numbers.
f32toa_string	Low-level string exporter for numbers.
f64toa_unsafe⚠	Unsafe, C-like exporter for float numbers.
f64toa_string	Low-level string exporter for numbers.