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digitalmars.D.bugs - [Issue 16344] New: Real FP magic on windows


          Issue ID: 16344
           Summary: Real FP magic on windows
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: greensunny12 gmail.com

Consider the following program:

void main
    import std.stdio;
    import std.math;
    alias S = real;
    S f = 0x1.14ada3f2c1d77p-48;
    writefln("up: %a", f.nextUp);
    writefln("down: %a", f.nextDown);
    writefln("f: %a", f);

On Windows it prints the same number.

up: 0x1.14ada3f2c1d77p-48
down: 0x1.14ada3f2c1d77p-48
f: 0x1.14ada3f2c1d77p-48

On Linux for 32-bit as well as 64-bit it prints the expected result:

up: 0x8.a56d1f960ebb801p-51
down: 0x8.a56d1f960ebb7ffp-51
f: 0x8.a56d1f960ebb8p-51

If I digged correctly, core.stdc.stdio.fwrite is used under the hood of
std.format (and thus writef). Unfortunately I don't have a Windows machine to
test this further. 

From the documentation for '%a':
 If there is no Precision, as many hexadecimal digits as necessary to exactly
represent the mantissa are generated.
Jul 31 2016