[Bug middle-end/51446] -fno-trapping-math generates NaN constant with different sign

[lucier at math dot purdue.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51446

--- Comment #10 from lucier at math dot purdue.edu 2011-12-08 18:32:56 UTC ---
Near the end of section 5.3.2 of 

Book E:
Enhanced PowerPC Architecture
Version 1.0
May 7, 2002

it says

Any instruction that generates a QNaN as the result of a disabled Invalid
Operation must generate this QNaN (i.e., 0x7FF8_0000_0000_0000).

The string x7ff8 does not otherwise occur in the manual.

The book

PowerPC User Instruction Set Architecture
Book I
Version 2.02
January 28, 2005

has the same text.

And a small test on my 10-year-old Mac Cube with a G4 powerpc processor shows
that the results have sign bit = 0, i.e., the output is

9221120237041090560 9221120237041090560

So the result is architecture dependent.

Blah.

Brad