NumPy core libraries¶
1.3.0 新版功能.
Starting from numpy 1.3.0, we are working on separating the pure C, “computational” code from the python dependent code. The goal is twofolds: making the code cleaner, and enabling code reuse by other extensions outside numpy (scipy, etc…).
NumPy core math library¶
The numpy core math library (‘npymath’) is a first step in this direction. This library contains most mathrelated C99 functionality, which can be used on platforms where C99 is not well supported. The core math functions have the same API as the C99 ones, except for the npy_* prefix.
The available functions are defined in <numpy/npy_math.h>  please refer to this header when in doubt.
Floating point classification¶

NPY_NAN
¶ This macro is defined to a NaN (Not a Number), and is guaranteed to have the signbit unset (‘positive’ NaN). The corresponding single and extension precision macro are available with the suffix F and L.

NPY_INFINITY
¶ This macro is defined to a positive inf. The corresponding single and extension precision macro are available with the suffix F and L.

NPY_PZERO
¶ This macro is defined to positive zero. The corresponding single and extension precision macro are available with the suffix F and L.

NPY_NZERO
¶ This macro is defined to negative zero (that is with the sign bit set). The corresponding single and extension precision macro are available with the suffix F and L.

int
npy_isnan
(x)¶ This is a macro, and is equivalent to C99 isnan: works for single, double and extended precision, and return a non 0 value is x is a NaN.

int
npy_isfinite
(x)¶ This is a macro, and is equivalent to C99 isfinite: works for single, double and extended precision, and return a non 0 value is x is neither a NaN nor an infinity.

int
npy_isinf
(x)¶ This is a macro, and is equivalent to C99 isinf: works for single, double and extended precision, and return a non 0 value is x is infinite (positive and negative).

int
npy_signbit
(x)¶ This is a macro, and is equivalent to C99 signbit: works for single, double and extended precision, and return a non 0 value is x has the signbit set (that is the number is negative).

double
npy_copysign
(double x, double y)¶ This is a function equivalent to C99 copysign: return x with the same sign as y. Works for any value, including inf and nan. Single and extended precisions are available with suffix f and l.
1.4.0 新版功能.
Useful math constants¶
The following math constants are available in npy_math.h. Single and extended precision are also available by adding the F and L suffixes respectively.

NPY_E
¶ Base of natural logarithm ()

NPY_LOG2E
¶ Logarithm to base 2 of the Euler constant ()

NPY_LOG10E
¶ Logarithm to base 10 of the Euler constant ()

NPY_LOGE2
¶ Natural logarithm of 2 ()

NPY_LOGE10
¶ Natural logarithm of 10 ()

NPY_PI
¶ Pi ()

NPY_PI_2
¶ Pi divided by 2 ()

NPY_PI_4
¶ Pi divided by 4 ()

NPY_1_PI
¶ Reciprocal of pi ()

NPY_2_PI
¶ Two times the reciprocal of pi ()

NPY_EULER
¶  The Euler constant
Lowlevel floating point manipulation¶
Those can be useful for precise floating point comparison.

double
npy_nextafter
(double x, double y)¶ This is a function equivalent to C99 nextafter: return next representable floating point value from x in the direction of y. Single and extended precisions are available with suffix f and l.
1.4.0 新版功能.

double
npy_spacing
(double x)¶ This is a function equivalent to Fortran intrinsic. Return distance between x and next representable floating point value from x, e.g. spacing(1) == eps. spacing of nan and +/ inf return nan. Single and extended precisions are available with suffix f and l.
1.4.0 新版功能.

void
npy_set_floatstatus_divbyzero
()¶ Set the divide by zero floating point exception
1.6.0 新版功能.

void
npy_set_floatstatus_overflow
()¶ Set the overflow floating point exception
1.6.0 新版功能.

void
npy_set_floatstatus_underflow
()¶ Set the underflow floating point exception
1.6.0 新版功能.

void
npy_set_floatstatus_invalid
()¶ Set the invalid floating point exception
1.6.0 新版功能.

int
npy_get_floatstatus
()¶ Get floating point status. Returns a bitmask with following possible flags:
 NPY_FPE_DIVIDEBYZERO
 NPY_FPE_OVERFLOW
 NPY_FPE_UNDERFLOW
 NPY_FPE_INVALID
Note that
npy_get_floatstatus_barrier
is preferable as it prevents agressive compiler optimizations reordering the call relative to the code setting the status, which could lead to incorrect results.1.9.0 新版功能.

int
npy_get_floatstatus_barrier
(char*)¶ Get floating point status. A pointer to a local variable is passed in to prevent aggresive compiler optimizations from reodering this function call relative to the code setting the status, which could lead to incorrect results.
Returns a bitmask with following possible flags:
 NPY_FPE_DIVIDEBYZERO
 NPY_FPE_OVERFLOW
 NPY_FPE_UNDERFLOW
 NPY_FPE_INVALID
1.15.0 新版功能.

int
npy_clear_floatstatus
()¶ Clears the floating point status. Returns the previous status mask.
Note that
npy_clear_floatstatus_barrier
is preferable as it prevents agressive compiler optimizations reordering the call relative to the code setting the status, which could lead to incorrect results.1.9.0 新版功能.

int
npy_clear_floatstatus_barrier
(char*)¶ Clears the floating point status. A pointer to a local variable is passed in to prevent aggresive compiler optimizations from reodering this function call. Returns the previous status mask.
1.15.0 新版功能.
Complex functions¶
1.4.0 新版功能.
C99like complex functions have been added. Those can be used if you wish to implement portable C extensions. Since we still support platforms without C99 complex type, you need to restrict to C90compatible syntax, e.g.:
/* a = 1 + 2i \*/
npy_complex a = npy_cpack(1, 2);
npy_complex b;
b = npy_log(a);
Linking against the core math library in an extension¶
1.4.0 新版功能.
To use the core math library in your own extension, you need to add the npymath compile and link options to your extension in your setup.py:
>>> from numpy.distutils.misc_util import get_info
>>> info = get_info('npymath')
>>> config.add_extension('foo', sources=['foo.c'], extra_info=info)
In other words, the usage of info is exactly the same as when using blas_info and co.
Halfprecision functions¶
2.0.0 新版功能.
The header file <numpy/halffloat.h> provides functions to work with IEEE 7542008 16bit floating point values. While this format is not typically used for numerical computations, it is useful for storing values which require floating point but do not need much precision. It can also be used as an educational tool to understand the nature of floating point roundoff error.
Like for other types, NumPy includes a typedef npy_half for the 16 bit float. Unlike for most of the other types, you cannot use this as a normal type in C, since it is a typedef for npy_uint16. For example, 1.0 looks like 0x3c00 to C, and if you do an equality comparison between the different signed zeros, you will get 0.0 != 0.0 (0x8000 != 0x0000), which is incorrect.
For these reasons, NumPy provides an API to work with npy_half values accessible by including <numpy/halffloat.h> and linking to ‘npymath’. For functions that are not provided directly, such as the arithmetic operations, the preferred method is to convert to float or double and back again, as in the following example.
npy_half sum(int n, npy_half *array) {
float ret = 0;
while(n) {
ret += npy_half_to_float(*array++);
}
return npy_float_to_half(ret);
}
External Links:
 7542008 IEEE Standard for FloatingPoint Arithmetic
 Halfprecision Float Wikipedia Article.
 OpenGL Half Float Pixel Support
 The OpenEXR image format.

NPY_HALF_ZERO
¶ This macro is defined to positive zero.

NPY_HALF_PZERO
¶ This macro is defined to positive zero.

NPY_HALF_NZERO
¶ This macro is defined to negative zero.

NPY_HALF_ONE
¶ This macro is defined to 1.0.

NPY_HALF_NEGONE
¶ This macro is defined to 1.0.

NPY_HALF_PINF
¶ This macro is defined to +inf.

NPY_HALF_NINF
¶ This macro is defined to inf.

NPY_HALF_NAN
¶ This macro is defined to a NaN value, guaranteed to have its sign bit unset.

float
npy_half_to_float
(npy_half h)¶ Converts a halfprecision float to a singleprecision float.

double
npy_half_to_double
(npy_half h)¶ Converts a halfprecision float to a doubleprecision float.

npy_half
npy_float_to_half
(float f)¶ Converts a singleprecision float to a halfprecision float. The value is rounded to the nearest representable half, with ties going to the nearest even. If the value is too small or too big, the system’s floating point underflow or overflow bit will be set.

npy_half
npy_double_to_half
(double d)¶ Converts a doubleprecision float to a halfprecision float. The value is rounded to the nearest representable half, with ties going to the nearest even. If the value is too small or too big, the system’s floating point underflow or overflow bit will be set.

int
npy_half_eq
(npy_half h1, npy_half h2)¶ Compares two halfprecision floats (h1 == h2).

int
npy_half_ne
(npy_half h1, npy_half h2)¶ Compares two halfprecision floats (h1 != h2).

int
npy_half_le
(npy_half h1, npy_half h2)¶ Compares two halfprecision floats (h1 <= h2).

int
npy_half_lt
(npy_half h1, npy_half h2)¶ Compares two halfprecision floats (h1 < h2).

int
npy_half_ge
(npy_half h1, npy_half h2)¶ Compares two halfprecision floats (h1 >= h2).

int
npy_half_gt
(npy_half h1, npy_half h2)¶ Compares two halfprecision floats (h1 > h2).

int
npy_half_eq_nonan
(npy_half h1, npy_half h2)¶ Compares two halfprecision floats that are known to not be NaN (h1 == h2). If a value is NaN, the result is undefined.

int
npy_half_lt_nonan
(npy_half h1, npy_half h2)¶ Compares two halfprecision floats that are known to not be NaN (h1 < h2). If a value is NaN, the result is undefined.

int
npy_half_le_nonan
(npy_half h1, npy_half h2)¶ Compares two halfprecision floats that are known to not be NaN (h1 <= h2). If a value is NaN, the result is undefined.

int
npy_half_iszero
(npy_half h)¶ Tests whether the halfprecision float has a value equal to zero. This may be slightly faster than calling npy_half_eq(h, NPY_ZERO).

int
npy_half_isnan
(npy_half h)¶ Tests whether the halfprecision float is a NaN.

int
npy_half_isinf
(npy_half h)¶ Tests whether the halfprecision float is plus or minus Inf.

int
npy_half_isfinite
(npy_half h)¶ Tests whether the halfprecision float is finite (not NaN or Inf).

int
npy_half_signbit
(npy_half h)¶ Returns 1 is h is negative, 0 otherwise.

npy_half
npy_half_copysign
(npy_half x, npy_half y)¶ Returns the value of x with the sign bit copied from y. Works for any value, including Inf and NaN.

npy_half
npy_half_spacing
(npy_half h)¶ This is the same for halfprecision float as npy_spacing and npy_spacingf described in the lowlevel floating point section.

npy_half
npy_half_nextafter
(npy_half x, npy_half y)¶ This is the same for halfprecision float as npy_nextafter and npy_nextafterf described in the lowlevel floating point section.

npy_uint16
npy_floatbits_to_halfbits
(npy_uint32 f)¶ Lowlevel function which converts a 32bit singleprecision float, stored as a uint32, into a 16bit halfprecision float.

npy_uint16
npy_doublebits_to_halfbits
(npy_uint64 d)¶ Lowlevel function which converts a 64bit doubleprecision float, stored as a uint64, into a 16bit halfprecision float.

npy_uint32
npy_halfbits_to_floatbits
(npy_uint16 h)¶ Lowlevel function which converts a 16bit halfprecision float into a 32bit singleprecision float, stored as a uint32.

npy_uint64
npy_halfbits_to_doublebits
(npy_uint16 h)¶ Lowlevel function which converts a 16bit halfprecision float into a 64bit doubleprecision float, stored as a uint64.