On 2/20/19 6:49 AM, Pierre Labastie via blfs-dev wrote:
On 20/02/2019 09:32, Ken Moffat via blfs-dev wrote:
On Wed, Feb 20, 2019 at 08:05:46AM +0000, Ken Moffat via blfs-dev wrote:
A few nits about the Command Explanations:
For --enable-float we mention RawTherapee, and then say
"These versions are not usable by packages in this book which use
libfftw3 so if you need both you will need to build fftw twice."
I think we should add Pulseaudio to the float option, and mention it
first because it is in the book ? Or maybe just mention "e.g.
pulse" since we are now building that version so it will be there
for RawTherappe and anything else ?
And drop that last sentence because we are now building it three
times.
But does anyone know what packages use the long double version ?
All I can find is questions on Stack Overflow etc where people are
writing their own C programs.
Hmm, since single-precision is float (as compared to double which is
not floating-point), and produces the libfftw3f* libs, make also
change 'Now build single-precision' to 'Now build floating-point' ?
Alternative suggestion: change "single precision" to "floating
point" and then just drop the explanation of --enable-float because
it should now be obvious, and maybe drop the additional explamation
of what uses the threaded double library.
ĸen
Hi,
Not sure what to do for the problem at hand. All I know is that double *is*
floating point...
Short version: the 3 flavours of fftw are all floating point.
Long version:
C has had a long history. At the beginning, the only floating point format was
32 bit and named "float". The computers ability at the time did not allow
more, although the accuracy is only about 7 digits, which is not enough for
reliable calculations. Soon after came the 64 bit floating point format, which
got named "double" in C (a short name for "double precision" (the fortran
name), not "double float", as one could imagine). This allowed for more
reliable number crunching, at the expanse of a computing time multiplied by 4.
Then came the 80 bit format used in Intel math coprocessors (no special name
in C), then 128 bit, more recently, named "long double" in C. Real time Fast
Fourier Transform (FFT) still use the 32 bit format (float), because it's
faster, but normal number crunching uses 64 bit, and 128 bit, or even MPFR
when higher precision is needed.
But the default libraries are double precision. Some modern CPUs have
512-bit registers that can be used for extreme precision or can take 8
doubles for parallel execution.
I prefer to maintain the single precision terminology as teh term
'float' can be overloaded to mean any floating point precision.
-- bruce
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