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digitalmars.D.learn - How to serialize a double.

reply Jake Pittis <jakepittis gmail.com> writes:
How do I convert a double to a ubyte[]?

I've tried all sorts of things including converting the double to 
a ulong and trying to serialize the ulong. For example test 
bellow fails.

````
unittest {
     double d = 3.14;
     ulong l = *cast(ulong*)(&d);
     double after = *cast(double*)(&l));
     assert(after == d); // This fails.
}
````
Nov 30 2016
next sibling parent Jerry <hurricane hereiam.com> writes:
On Thursday, 1 December 2016 at 00:36:30 UTC, Jake Pittis wrote:

 How do I convert a double to a ubyte[]?

 I've tried all sorts of things including converting the double 
 to a ulong and trying to serialize the ulong. For example test 
 bellow fails.

 ````
 unittest {
     double d = 3.14;
     ulong l = *cast(ulong*)(&d);
     double after = *cast(double*)(&l));
     assert(after == d); // This fails.
 }
 ````


That test passes for me, are you sure there isn't something else 
wrong with your code? Check to see if it works for just a ulong 
that has values in it's upper 32-bits?
Nov 30 2016
prev sibling next sibling parent "H. S. Teoh via Digitalmars-d-learn" <digitalmars-d-learn puremagic.com> writes:
On Thu, Dec 01, 2016 at 12:36:30AM +0000, Jake Pittis via Digitalmars-d-learn
wrote:

 How do I convert a double to a ubyte[]?
 
 I've tried all sorts of things including converting the double to a
 ulong and trying to serialize the ulong. For example test bellow
 fails.
 
 ````
 unittest {
     double d = 3.14;
     ulong l = *cast(ulong*)(&d);
     double after = *cast(double*)(&l));
     assert(after == d); // This fails.
 }
 ````


	union U
	{
		ubyte[double.sizeof] bytes;
		double d;
	}
	U u, v;

	u.d = 3.14159;

	v.bytes[] = u.bytes[];
	assert(v.d == 3.14159);


T

-- 
Those who don't understand Unix are condemned to reinvent it, poorly.
Nov 30 2016
prev sibling next sibling parent Basile B. <b2.temp gmx.com> writes:
On Thursday, 1 December 2016 at 00:36:30 UTC, Jake Pittis wrote:

 How do I convert a double to a ubyte[]?

 I've tried all sorts of things including converting the double 
 to a ulong and trying to serialize the ulong. For example test 
 bellow fails.

 ````
 unittest {
     double d = 3.14;
     ulong l = *cast(ulong*)(&d);
     double after = *cast(double*)(&l));
     assert(after == d); // This fails.
 }
 ````


platform, archi, compiler version ?
Nov 30 2016
prev sibling parent reply Bauss <jj_1337 live.dk> writes:
On Thursday, 1 December 2016 at 00:36:30 UTC, Jake Pittis wrote:

 How do I convert a double to a ubyte[]?

 I've tried all sorts of things including converting the double 
 to a ulong and trying to serialize the ulong. For example test 
 bellow fails.

 ````
 unittest {
     double d = 3.14;
     ulong l = *cast(ulong*)(&d);
     double after = *cast(double*)(&l));
     assert(after == d); // This fails.
 }
 ````


You could do something like below which will allow you to 
serialize any number.

````
import std.stdio : writeln;
import std.traits : isNumeric;

ubyte[] bytes(T)(T num) if (isNumeric!T) {
	auto buf = new ubyte[T.sizeof];
	
	(*cast(T*)(buf.ptr)) = num;
	
	return buf;
}

T value(T)(ubyte[] buf) if (isNumeric!T) {
	return (*cast(T*)(buf.ptr));
}
````

And example usage:
````
double foo = 3.14;

writeln(foo); // Prints 3.14

ubyte[] bar = foo.bytes;

writeln(bar); // Prints the bytes equal to 3.14

foo = bar.value!double;

writeln(foo); // Prints 3.14
````
Nov 30 2016
parent Jake Pittis <jakepittis gmail.com> writes:
On Thursday, 1 December 2016 at 07:13:45 UTC, Bauss wrote:

 On Thursday, 1 December 2016 at 00:36:30 UTC, Jake Pittis wrote:

 [...]


 You could do something like below which will allow you to 
 serialize any number.

 ````
 import std.stdio : writeln;
 import std.traits : isNumeric;

 ubyte[] bytes(T)(T num) if (isNumeric!T) {
 	auto buf = new ubyte[T.sizeof];
 	
 	(*cast(T*)(buf.ptr)) = num;
 	
 	return buf;
 }

 T value(T)(ubyte[] buf) if (isNumeric!T) {
 	return (*cast(T*)(buf.ptr));
 }
 ````

 And example usage:
 ````
 double foo = 3.14;

 writeln(foo); // Prints 3.14

 ubyte[] bar = foo.bytes;

 writeln(bar); // Prints the bytes equal to 3.14

 foo = bar.value!double;

 writeln(foo); // Prints 3.14
 ````


Regarding the test assertion that failed. Turns out I had a bug 
in the test. (of course)
This last solution is very pretty. Thanks.

You folks are all so kind!
Dec 01 2016