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# System configuration

When NumPy is built, information about system configuration is recorded, and is made available for extension modules using NumPy’s C API. These are mostly defined in `numpyconfig.h` (included in `ndarrayobject.h`). The public symbols are prefixed by `NPY_*`. NumPy also offers some functions for querying information about the platform in use.

For private use, NumPy also constructs a `config.h` in the NumPy include directory, which is not exported by NumPy (that is a python extension which use the numpy C API will not see those symbols), to avoid namespace pollution.

## Data type sizes

The `NPY_SIZEOF_{CTYPE}` constants are defined so that sizeof information is available to the pre-processor.

NPY_SIZEOF_SHORT

  sizeof(short)

NPY_SIZEOF_INT

  sizeof(int)

NPY_SIZEOF_LONG

  sizeof(long)

NPY_SIZEOF_LONGLONG

  sizeof(longlong) where longlong is defined appropriately on the platform.

NPY_SIZEOF_PY_LONG_LONG

NPY_SIZEOF_FLOAT

  sizeof(float)

NPY_SIZEOF_DOUBLE

  sizeof(double)

NPY_SIZEOF_LONG_DOUBLE

NPY_SIZEOF_LONGDOUBLE

  sizeof(longdouble)

NPY_SIZEOF_PY_INTPTR_T

  Size of a pointer `void *` and `intptr_t`/`Py_intptr_t`.

NPY_SIZEOF_INTP

  Size of a `size_t` on this platform (`sizeof(size_t)`)

## Platform information

NPY_CPU_X86

NPY_CPU_AMD64

NPY_CPU_IA64

NPY_CPU_PPC

NPY_CPU_PPC64

NPY_CPU_SPARC

NPY_CPU_SPARC64

NPY_CPU_S390

NPY_CPU_PARISC

  CPU architecture of the platform; only one of the above is defined.

  Defined in `numpy/npy_cpu.h`

NPY_LITTLE_ENDIAN

NPY_BIG_ENDIAN

NPY_BYTE_ORDER

  Portable alternatives to the `endian.h` macros of GNU Libc. If big endian, `NPY_BYTE_ORDER` == `NPY_BIG_ENDIAN`, and similarly for little endian architectures.

  Defined in `numpy/npy_endian.h`.

int PyArray_GetEndianness()

  Returns the endianness of the current platform. One of `NPY_CPU_BIG`, `NPY_CPU_LITTLE`, or `NPY_CPU_UNKNOWN_ENDIAN`.

  NPY_CPU_BIG
  NPY_CPU_LITTLE
  NPY_CPU_UNKNOWN_ENDIAN

## Compiler directives

NPY_LIKELY

NPY_UNLIKELY

NPY_UNUSED