Subject: Re: accuracy of "long double"
To: Neil Booth <>
From: None <>
List: tech-toolchain
Date: 08/29/2007 11:29:03
Selon Neil Booth <>:

> Which means the only one that follows IEEE by default is long double
> on Linux.  You could get the same on NetBSD by changing the CPU
> flags so that you have long double precision.
> You can't get IEEE behaviour for double on x86 without SSE2.

Sorry for being still more inquisitive, I still have two further questions:

1. If I understand correctly, <long double> on NetBSD will NOT behave as IEEE
80-bit precision should do. Does it mean that <long double> = <double>, or just
that the rounding prescriptions of <long double> are not honored?

2. If I compile the code with gcc -mfpmath=sse -msse2 [...] (as I usually do) do
I get the right behaviour for <double> and <long double>?

3. Is there a penalty, in terms of performance, to incur by switching from
default x86 <double> precision to full <long double> precision?

Thanks again