Precision - FFTW 3.3.3

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4.1.2 Precision

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Chris@10: You can install single and long-double precision versions of FFTW, Chris@10: which replace double with float and long double, Chris@10: respectively (see Installation and Customization). To use these Chris@10: interfaces, you: Chris@10: Chris@10:

Link to the single/long-double libraries; on Unix, -lfftw3f or Chris@10: -lfftw3l instead of (or in addition to) -lfftw3. (You Chris@10: can link to the different-precision libraries simultaneously.) Chris@10: Chris@10:
Include the same <fftw3.h> header file. Chris@10: Chris@10:
Replace all lowercase instances of ‘fftw_’ with ‘fftwf_’ or Chris@10: ‘fftwl_’ for single or long-double precision, respectively. Chris@10: (fftw_complex becomes fftwf_complex, fftw_execute Chris@10: becomes fftwf_execute, etcetera.) Chris@10: Chris@10:
Uppercase names, i.e. names beginning with ‘FFTW_’, remain the Chris@10: same. Chris@10: Chris@10:
Replace double with float or long double for Chris@10: subroutine parameters. Chris@10: Chris@10:

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Depending upon your compiler and/or hardware, long double may not Chris@10: be any more precise than double (or may not be supported at all, Chris@10: although it is standard in C99). Chris@10: Chris@10: Chris@10:

We also support using the nonstandard __float128 Chris@10: quadruple-precision type provided by recent versions of gcc on Chris@10: 32- and 64-bit x86 hardware (see Installation and Customization). Chris@10: To use this type, link with -lfftw3q -lquadmath -lm (the Chris@10: libquadmath library provided by gcc is needed for Chris@10: quadruple-precision trigonometric functions) and use ‘fftwq_’ Chris@10: identifiers. Chris@10: Chris@10: Chris@10: Chris@10: