[Issue 3928] New: Comparing imaginaries with reals produces results that are inconsistent

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=3928

           Summary: Comparing imaginaries with reals produces results that
                    are inconsistent
           Product: D
           Version: 2.041
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: crimson.magus at gmail.com


--- Comment #0 from Aldo Nunez <crimson.magus at gmail.com> 2010-03-10 12:04:36 PST ---
Comparing an imaginary number like an ifloat with a real one like a float:
1. Has results that differ at compile time and runtime.
2. At runtime is done in the wrong order.
3. Doesn't seem to be very meaningful, given that you can't compare complex
numbers.

With respect to each issue above, here are some more details.

1. Different results at runtime and compile time.
At compile time, if the left is imaginary, then we take the imaginary part of
the right side and compare the two. If the left side is real, then we take the
real part of the right side and compare.
All of this is as seen in constfold.c.
At runtime, we turn both sides into complex numbers by making a missing part
zero. Then, we compare the imaginary parts, and if they're equal, compare the
real parts.

2. Wrong order at runtime.
In the runtime comparison described in #1 what's actually compared is right to
left instead of left to right. If my program has "a < b", then "b < a" is
checked.

3. Meaning?
Comparisons where at least one side is a complex number are not allowed in D.
As such, is it meaningful to allow the comparisons described here, given that
such numbers are treated as complex numbers and compared?

Note, all of this is strictly where one side of a compare expression is an
imaginary number and the other is a real number.


Here's a sample program:

import std.stdio;

void main()
{
        cfloat    cf1 = 1 + 2i;
        cfloat    cf2 = 3 + 4i;

        ifloat    if2 = 1i;
        float    f2 = 3;
        ifloat    if3 = 4i;
        float    f3 = 2;
        ifloat  if4 = 5i;
        float   f4 = 5;

        writeln( "--- < ---" );
        writeln( if2 < f2 );
        writeln( f2 < if2 );
        writeln( if3 < f3 );
        writeln( f3 < if3 );
        writeln( if4 < f4 );
        writeln( f4 < if4 );
        writeln( 1i < 3 );
        writeln( 3 < 1i );
        writeln( 4i < 2 );
        writeln( 2 < 4i );
        writeln( 5i < 5 );
        writeln( 5 < 5i );

        writeln( "--- == ---" );
        writeln( if2 == f2 );
        writeln( f2 == if2 );
        writeln( if3 == f3 );
        writeln( f3 == if3 );
        writeln( if4 == f4 );
        writeln( f4 == if4 );
        writeln( 1i == 3 );
        writeln( 3 == 1i );
        writeln( 4i == 2 );
        writeln( 2 == 4i );
        writeln( 5i == 5 );
        writeln( 5 == 5i );

        writeln( "--- > ---" );
        writeln( if2 > f2 );
        writeln( f2 > if2 );
        writeln( if3 > f3 );
        writeln( f3 > if3 );
        writeln( if4 > f4 );
        writeln( f4 > if4 );
        writeln( 1i > 3 );
        writeln( 3 > 1i );
        writeln( 4i > 2 );
        writeln( 2 > 4i );
        writeln( 5i > 5 );
        writeln( 5 > 5i );
}

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