js-hexfloat

js-hexfloat

Rudimentary C99 Hexadecimal Float Support in JS

SYNOPSIS

var pi = parseHexFloat('0x1.921fb54442d18p+1'); // 3.14159265358982
var piHex = Math.PI.toHexString();              // '0x3.243f6a8885a3p0'
parseHexFloat(piHex) == Math.PI;                // true

DESCRIPTION

This script adds the following:

parseHexFloat(theString)

Parses C99 hexadecimal floating point in theString. Returns NaN if fails.

Unlike parseInt and parseFloat, the number must be prepended with '0x' and ended with 'p' and exponent in decimal number.

also available as Number.parseHexFloat().

Number.prototype.toHexString(canonical)

Stringifies the number as a C99 hexadecimal notation. Analogous to "%a" in C99 sprintf().

CAVEAT

Unless canonical is true, the result is not canonical. Canonically the first digit of the number is always 1 and the sign of the exponent is never omitted.

printf("%a\n", -57005.7458343505859375); // prints -0x1.bd5b7ddep+15

On the other hand, this implementation takes advangage of the fact Number.prototype.toString(16) works for floating point numbers. It just checks the number is negative and prepends '-' if so, then prepend '0x', and append 'p0'.

console.log((-57005.7458343505859375).toHexString());     // -0xdead.beefp0
console.log((-57005.7458343505859375).toHexString(true)); // -0x1.bd5b7ddep+15

Even when not canonical, you can use the result interchangeably with C99 and other platforms that support the notation (C++11, Ruby, Perl 5.22 ...).

SEE ALSO

• http://en.cppreference.com/w/c/language/floating_constant
• https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/TheBasics.html
• http://search.cpan.org/dist/perl-5.22.0/pod/perldelta.pod#Floating_point_parsing_has_been_improved