Need a way to convert bytes <-> double

[DartBot]

This issue was originally filed by [email protected]

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We need the equivalent of Java's Double.doubleToLongBits (also doubleToRawLongBits ) and longBitsToDouble. Without them, we cannot perform any kind of binary I/O on doubles.

It would be good to parse and emit 32-bit float values as well, even without a runtime float type.

[DartBot]

This comment was originally written by [email protected]

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Removed Type-Defect label.
Added Type-Enhancement, Area-Library, Triaged labels.

[lrhn]

Seems reasonable. It's possible to deduce the representation from the value, but with low-level support it will be faster.
Since ints can hold 64 bits without problems, a int bits <-> double conversion should be doable.

I think something like
 class double {
    factory double.fromBits(int bits64);
    ..
    int toBits();
 }

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Added this to the M2 milestone.
Added Accepted label.

[lrhn]

This will not be implementable in dart2js as long as it uses only JS doubles as integers (no big-int support).
Another option is to have:
  class double {
    double.fromParts(sign, exponent, mantissa) => sign * Math.pow(2, exponent) * mantissa;
    int get exponent; // returns a number in the range -1023..1024 (with 1024 being reserved for non-finites)
    int get sign; // return +1 or -1
    double get mantissa; // Returns a number in the range [0..2[, with [0..1[ values only for denormals.
    ...
  }

[ghost]

We could use dart:scalarlist's UInt8List to hold the result of a conversion double -> bytes (native call?). I think more efficient would be converting Float64List <-> Uint8List.

[floitschG]

Removed this from the M2 milestone.
Added this to the M3 milestone.

[anders-sandholm]

Removed this from the M3 milestone.
Added this to the M4 milestone.

[lrhn]

I think we should rely on typed-data for this, and not build something into double. The use-case is rare enough that a few extra operations won't hurt.

[floitschG]

Eventually, when we don't need to think about dart2js anymore we can reconsider.

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Added WontFix label.