Re: [dart-misc] How convert double or num into binary presentation? To int64 or to int32 or into bytes?

[Lasse R.H. Nielsen]

There is currently no functionality to do that in the libraries.
It is under consideration to add a double.asBits (or some other name).
That won't work in the dart2js compiler because it doesn't support
real integers yet (only doubles, which can't contain a 64-bit value).

If you desperately need it now, you can use the following code to
convert a double to its bits arithmetically:

int doubleToBits(double value) {
const pow52 = 4503599627370496.0; // 2^52
const pow1022 = 4.49423283715579e+307; // 2^1022
if (value.isNaN()) {
return 0x7FF8000000000000;
}
int signbit = 0;
if (value.isNegative()) {
signbit = 0x8000000000000000;
value = -value;
}
if (value.isInfinite()) {
return signbit | 0x7FF0000000000000;
} else if (value < 2.2250738585072014e-308) {
// Denormal or zero.
// Multiply by 2^(1022+52) to get the bits into the correct position.
int bits = (value * pow1022 * pow52).toInt();
return signbit | bits;
} else {
// Slow linear search to move bits into correct position for mantissa.
// Use binary search or something even smarter for speed.
int exponent = 52;
while (value < pow52) {
value *= 2;
exponent -= 1;
}
while (value >= pow52 * 2) {
value /= 2;
exponent += 1;
}
int mantissaBits = (value - pow52).toInt();
int exponentBits = (exponent + 1023);
return signbit | (exponentBits << 52) | mantissaBits;
}
}


(Again: This does NOT work in dart2js, you need 64-bit unsigned
integers for it to work.)

[Ladislav Thon]

There is currently no functionality to do that in the libraries.

Except that there is :-)

I needed this too in my MsgPack implementation and I realized that ByteArray and companions are perfectly suitable for this. Something like (new Float64Array(1)..[0] = doubleValue).asByteArray() (writing this from memory) gives you 8-element list of bytes. Converting it to Int64Array for getting a 64bit integer is left for the reader as an excersise (I didn't need this).

LT

[Mads Ager]

As Ladislav points out there is a VM-only library that will let you
perform operations like these.

http://api.dartlang.org/docs/continuous/dart_scalarlist.html

In order to have access to these types you need to import
dart:scalarlist (maybe not in the current SDK, but definitely in the
next release).

Cheers, -- Mads

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