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4.1.2 Precision

You can install single and long-double precision versions of FFTW, which replace double with float and long double, respectively (see Installation and Customization). To use these interfaces, you:

Depending upon your compiler and/or hardware, long double may not be any more precise than double (or may not be supported at all, although it is standard in C99).

We also support using the nonstandard __float128 quadruple-precision type provided by recent versions of gcc on 32- and 64-bit x86 hardware (see Installation and Customization). To use this type, link with -lfftw3q -lquadmath -lm (the libquadmath library provided by gcc is needed for quadruple-precision trigonometric functions) and use ‘fftwq_’ identifiers.