[Numpy-discussion] Proposal: Deprecate np.int, np.float, etc.?
Sturla Molden
sturla.molden at gmail.com
Fri Jul 31 13:45:01 EDT 2015
Chris Barker <chris.barker at noaa.gov> wrote:
> What about Fortan -- I've been out of that loop for ages -- does
> semi-modern Fortran use well defined integer types?
Modern Fortran is completely sane.
INTEGER without kind number (Fortran 77) is the fastest integer on the CPU.
On AMD64 that is 32 bit, because it is designed to use a 64 bit pointer
with a 32 bit offset. (That is also why Microsoft decided to use a 32 bit
long, because it by definition is the fastest integer of at least 32 bits.
One can actually claim that the C standard is violated with a 64 bit long
on AMD64.) Because of this we use a 32 bit interger in BLAS and LAPACK
linked to NumPy and SciPy.
The function KIND (Fortran 90) allows us to query the kind number of a
given variable, e.g. to find out the size of INTEGER and REAL.
The function SELECTED_INT_KIND (Fortran 90) returns the kind number of
smallest integer with a specified range.
The function SELECTED_REAL_KIND (Fortran 90) returns the kind number of
smallest float with a given range and precision. THe returned kind number
can be used for REAL and COMPLEX.
KIND, SELECTED_INT_KIND and SELECTED_REAL_KIND will all return compile-time
constants, and can be used to declare other variables if the return value
is stored in a variable with the attribute PARAMETER. This allows te
programmer to get the REAL, COMPLEX or INTEGER the algorithm needs
numerically, without thinking about how big they need to be in bits.
ISO_C_BINDING is a Fortran 2003 module which contains kind numbers
corresponding to all C types, including size_t and void*, C structs, an
attribute for using pass-by-value semantics, controlling the C name to
avoid name mangling, as well as functions for converting between C and
Fortran pointers. It allows portable interop between C and Fortran (either
calling C from Fortran or calling Fortran from C).
ISO_FORTRAN_ENV is a Fortran 2003 and 2008 module. In F2003 it contain kind
numbers for integers with specified size: INT8, INT16, INT32, and INT64. In
F2008 it also contains kind numbers for IEEE floating point types: REAL32,
REAL64, and REAL128. The kind numbers for floating point types can also be
used to declare complex numbers.
So with modern Fortran we have a completely portable and unambiguous type
system.
C11/C++11 is sane as well, but not quite as sane as that of modern Fortran.
Sturla
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