[dmd-internals] 64bit bad codegen from ulong pointers.

Don Clugston dclugston at googlemail.com
Tue Jan 4 13:18:51 PST 2011


Aargh, it was an incorrect reduction. Here's an larger case which
fails with the latest DMD, Phobos, and druntime.
(Reducing test cases is a bit painful through a remote connection).
-------------
double nextUpw(double x) @trusted nothrow
{
    ulong *ps = cast(ulong *)&x;

    if ((*ps & 0x7FF0_0000_0000_0000) == 0x7FF0_0000_0000_0000) {
        if (x == -x.infinity) return  -x.max;
        return x;
    }
    if (!(*ps & 0x8000_0000_0000_0000L))  {
         assert(x>=0);
    }
    return x;
}

void main()
{
  nextUpw(-double.min_normal*(1.0 - double.epsilon));
}
=========

On 3 January 2011 23:37, Walter Bright <walter at digitalmars.com> wrote:
> Works when I try it. Do you have the latest dmd?
>
> Don Clugston wrote:
>>
>> Reduced test case  from std.math. *ps is 0x800F_FFFF_FFFF_FFFF, yet
>> the if() branch is not taken.
>> This one looks as though it might be the root cause of many failures.
>>
>> void check(double x)
>> {
>> ulong *ps = cast(ulong *)&x;
>> if (*ps & 0x8000_0000_0000_0000) {}
>> else assert(x>=0);
>> }
>>
>> void main()
>> {
>>  check(-double.min_normal*double.epsilon);
>> }
>>
>>
>
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