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-rw-r--r--libraries/fftw/README11
1 files changed, 9 insertions, 2 deletions
diff --git a/libraries/fftw/README b/libraries/fftw/README
index c357014303..10b6bff214 100644
--- a/libraries/fftw/README
+++ b/libraries/fftw/README
@@ -4,5 +4,12 @@ symmetric, and parallel transforms, and can handle arbitrary array sizes
efficiently. FFTW is typically faster than other publically-available FFT
implementations, and is even competitive with vendor-tuned libraries.
-There are several machine-dependent optimizations that can be enabled in order
-to generate SIMD code; take a look in fftw.SlackBuild to enable them.
+By default non-portable binaries will be created. If you need to create
+a package that is shared among various machines, pass PORTABLE=yes to the
+script.
+
+To enable SSE or SSE2 SIMD optimizations pass SSE=yes or SSE2=yes respectively
+to the script. Enabling these will still create a portable package as fftw falls
+back to the standard code, if the optimized one isn't supported on the cpu.
+However, to be able to build them your cpu has to actually support those
+extensions.