float has too much precision
faux at amis.com
Tue Apr 21 20:36:08 UTC 2020
On 2020-04-21 22:10, Steven Schveighoffer wrote:
> On 4/21/20 3:47 PM, Faux Amis wrote:
>> I'm dumbfounded, why does the following code write '35' on DMD32 D
>> Compiler v2.091.0-dirty?
>> module magic;
>> float magic( float f )
>> return f + 35f - f;
>> void main()
>> import std.stdio;
>> writeln( magic(1_000_000_000f) );
> On run.dlang.io, it prints 64. Also on my mac.
> Possibly it's working because intermediate floating point calculations
> are generally done at max precision. On your system, that might be
> 80-bit reals.
> Also possible that some optimization is figuring out that it can just
> return 35f?
> Try instead:
> float magic( float f)
> float result = f + 35f;
> return result - f;
> Is it worth worrying about? floating point is supposed to be inexact and
> subject to variance on different machines.
No, it doesn't matter. I just wanted to understand why it happened.
It seems splitting it up did the trick. So intermediate it is.
More information about the Digitalmars-d-learn