How to determine if a Javascript Number is in a range with a single precision?

Question

According to the ECMAScript specification, Javascript values ​​correspond to the IEEE 754 double-precision value of 64-bit binary format.

For the WebIDL validator I'm working on now, I need to find out if a given numeric value can be converted to a WebIDL float , that is, if it can be represented as a final single-point 32-bit IEEE 754 value.

Currently, I decided to use the following approach:

validate: function(value) {
    if (typeof value !== 'number' || !Number.isFinite(value)) {
        return false;
    }

    if (value === 0) {
        return true;
    }

    var view = new DataView(new ArrayBuffer(4));

    view.setFloat32(0, value);

    var converted = view.getFloat32(0);
    var relativeError = Math.abs(value - converted) / value;

    return relativeError < Number.EPSILON;
}

In essence, I am doing this:

• Wrap DataViewaround 4 bytes ArrayBuffer.
• Save the value Numberas a 32-bit float in the buffer.
• Get the converted number back from the buffer.
• .
• , , epsilon , Number.EPSILON.

:

• Chrome, .
• , . .

, ? ? , ?

, . , 1.001, 3.14159 .. , epsilon epsilon 32- (2 ^-23) , 16777217.

, , (2 ²⁴ - (2 ²⁴)).

validate: function(value) {
    return typeof value === 'number' && Number.isFinite(value)
            && value >= -16777216 && value <= 16777216;
}

Answer 1

ECMAScript 6, Math.fround, , :

function isfloat32(x) {
  return isNaN(x) || x == Math.fround(x);
}

UPDATE: float WebIDL, ( Inf NaN).

function isfloat32(x) {
  return isFinite(x) && x == Math.fround(x);
}