annotate fft/fftw/fftw-3.3.4/CONVENTIONS @ 40:223f770b5341 kissfft-double tip

Try a double-precision kissfft

Code conventions used internally by fftw3 (not in API):

LEARN FROM THE MASTERS: read Ken Thompson's C compiler in Plan 9.
   Avoid learning from C++/Java programs.

INDENTATION: K&R, 5 spaces/tab.  In case of doubt, indent -kr -i5.

NAMES: keep them short.  Shorter than you think.  The Bible was written
   without vowels.  Don't outsmart the Bible.

   Common names:

   R       : real type, aka fftw_real
   E       : real type for local variables (possibly extra precision)
   C       : complex type
   sz      : size
   vecsz   : vector size
   is, os  : input/output stride
   ri, ii  : real/imag input (complex data)
   ro, io  : real/imag output (complex data)
   I, O    : real input/output (real data)
   A       : assert
   CK      : check
   S       : solver, defined internally to each solver file
   P       : plan, defined internally to each solver file
   k       : codelet
   X(...)  : used for mangling of external names (see below)
   K(...)  : floating-point constant, in E precision

   If a name is used often and must have the form fftw_foo to avoid
   namespace pollution, #define FOO fftw_foo and use the short name.

   Leave that hungarian crap to MS.  foo_t counts as hungarian: use
   foo instead.  foo is lowercase so that it does not look like a DOS
   program. Exception: typedef struct foo_s {...} foo;  instead of
   typedef struct foo {...} foo;  for C++ compatibility.

NAME MANGLING: use X(foo) for external names instead of fftw_foo.
    X(foo) expands to fftwf_foo or fftw_foo, depending on the
    precision.  (Unfortunately, this is a ugly form of hungarian
    notation.  Grrr...)  Names that are not exported do not need to be
    mangled.

REPEATED CODE: favor a table.  E.g., do not write

    foo("xxx", 1);
    foo("yyy", 2);
    foo("zzz", -1);

    Instead write

      struct { const char *nam, int arg } footab[] = {
	{ "xxx", 1 },
	{ "yyy", 2 },
	{ "zzz", -1 }
      };

    and loop over footab.  Rationale: it saves code space.
    Similarly, replace a switch statement with a table whenever
    possible.

C++: The code should compile as a C++ program. Run the code through
    gcc -xc++ .  The extra C++ restrictions are unnecessary, of
    course, but this will save us from a flood of complaints when
    we release the code.