2368Re: [buildcheapeeg] BWView
- Mar 1, 2002Jim,
According to the FFTW FAQ, the enable-i386-hacks is for double
The configure option --enable-i386-hacks enables specific
optimizations for the Pentium and later x86 CPUs under gcc,
which can significantly improve performance of double-
precision transforms. <snip> These hacks provide a workaround
to the incorrect alignment of local double variables in gcc.
The compiler aligns these variables to multiples of 4 bytes,
but execution is much faster (on Pentium and PentiumPro) if
doubles are aligned to a multiple of 8 bytes.
If we are doing only single precision transforms, perhaps
we don't need to enable the pentium hacks? There seems to
be some bugs in these hacks:
In principle, these hacks are no longer required under gcc
versions 2.95 and later, which automatically align the
stack correctly (see -mpreferred-stack-boundary in the gcc
manual). However, we have encountered a bug in the stack
alignment of versions 2.95. that causes FFTW's stack
to be misaligned under some circumstances. The configure
script automatically detects this bug and disables gcc's
stack alignment in favor of our own hacks when
--enable-i386-hacks is used.
Can we skip the enable-i386-hacks for single precision?
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