fast_float number parsing library: 4x faster than strtod

The fast_float library provides fast header-only implementations for the C++ from_chars functions for float and double types. These functions convert ASCII strings representing decimal values (e.g., 1.3e10) into binary types. We provide exact rounding (including round to even). In our experience, these fast_float functions many times faster than comparable number-parsing functions from existing C++ standard libraries.

Specifically, fast_float provides the following two functions with a C++17-like syntax (the library itself only requires C++11):

C++

from_chars_result from_chars(const char* first, const char* last, float& value, ...);
from_chars_result from_chars(const char* first, const char* last, double& value, ...);

The return type (from_chars_result) is defined as the struct:

C++

struct from_chars_result {
    const char* ptr;
    std::errc ec;
};

It parses the character sequence [first,last) for a number. It parses floating-point numbers expecting a locale-independent format equivalent to the C++17 from_chars function. The resulting floating-point value is the closest floating-point values (using either float or double), using the "round to even" convention for values that would otherwise fall right in-between two values. That is, we provide exact parsing according to the IEEE standard.

Given a successful parse, the pointer (ptr) in the returned value is set to point right after the parsed number, and the value referenced is set to the parsed value. In case of error, the returned ec contains a representative error, otherwise the default (std::errc()) value is stored.

The implementation does not throw and does not allocate memory (e.g., with new or malloc).

It will parse infinity and nan values.