Casting double to ulong weirdness

[Ali Çehreli via Digitalmars-d]

On 08/24/2015 11:06 AM, rumbu wrote:

 > BTW, 1.2 and 12.0 are directly representable as double

12 is but 1.2 is not.

 > In C++:
 >
 > printf("%.20f\r\n", 1.2);
 > printf("%.20f\r\n", 12.0);
 >
 > will output:
 >
 > 1.20000000000000000000
 > 12.00000000000000000000
 >
 > Either upcasting to real is the wrong decision here, either the writeln
 > string conversion is wrong.

Output is one thing. The issue is with the representation of 1.2. You 
need infinite digits. D's %a helps with visualizing it:

import std.stdio;

void main()
{
     writefln("%a", 1.2);
     writefln("%a", 12.0);
}

Outputs

0x1.3333333333333p+0
0x1.8p+3

Ali