1.. highlight:: c
2
3.. _floatobjects:
4
5Floating Point Objects
6----------------------
7
8.. index:: pair: object; floating point
9
10
11.. c:type:: PyFloatObject
12
13   This subtype of :c:type:`PyObject` represents a Python floating point object.
14
15
16.. c:var:: PyTypeObject PyFloat_Type
17
18   This instance of :c:type:`PyTypeObject` represents the Python floating point
19   type.  This is the same object as :class:`float` in the Python layer.
20
21
22.. c:function:: int PyFloat_Check(PyObject *p)
23
24   Return true if its argument is a :c:type:`PyFloatObject` or a subtype of
25   :c:type:`PyFloatObject`.  This function always succeeds.
26
27
28.. c:function:: int PyFloat_CheckExact(PyObject *p)
29
30   Return true if its argument is a :c:type:`PyFloatObject`, but not a subtype of
31   :c:type:`PyFloatObject`.  This function always succeeds.
32
33
34.. c:function:: PyObject* PyFloat_FromString(PyObject *str)
35
36   Create a :c:type:`PyFloatObject` object based on the string value in *str*, or
37   ``NULL`` on failure.
38
39
40.. c:function:: PyObject* PyFloat_FromDouble(double v)
41
42   Create a :c:type:`PyFloatObject` object from *v*, or ``NULL`` on failure.
43
44
45.. c:function:: double PyFloat_AsDouble(PyObject *pyfloat)
46
47   Return a C :c:expr:`double` representation of the contents of *pyfloat*.  If
48   *pyfloat* is not a Python floating point object but has a :meth:`__float__`
49   method, this method will first be called to convert *pyfloat* into a float.
50   If ``__float__()`` is not defined then it falls back to :meth:`__index__`.
51   This method returns ``-1.0`` upon failure, so one should call
52   :c:func:`PyErr_Occurred` to check for errors.
53
54   .. versionchanged:: 3.8
55      Use :meth:`__index__` if available.
56
57
58.. c:function:: double PyFloat_AS_DOUBLE(PyObject *pyfloat)
59
60   Return a C :c:expr:`double` representation of the contents of *pyfloat*, but
61   without error checking.
62
63
64.. c:function:: PyObject* PyFloat_GetInfo(void)
65
66   Return a structseq instance which contains information about the
67   precision, minimum and maximum values of a float. It's a thin wrapper
68   around the header file :file:`float.h`.
69
70
71.. c:function:: double PyFloat_GetMax()
72
73   Return the maximum representable finite float *DBL_MAX* as C :c:expr:`double`.
74
75
76.. c:function:: double PyFloat_GetMin()
77
78   Return the minimum normalized positive float *DBL_MIN* as C :c:expr:`double`.
79
80
81Pack and Unpack functions
82=========================
83
84The pack and unpack functions provide an efficient platform-independent way to
85store floating-point values as byte strings. The Pack routines produce a bytes
86string from a C :c:expr:`double`, and the Unpack routines produce a C
87:c:expr:`double` from such a bytes string. The suffix (2, 4 or 8) specifies the
88number of bytes in the bytes string.
89
90On platforms that appear to use IEEE 754 formats these functions work by
91copying bits. On other platforms, the 2-byte format is identical to the IEEE
92754 binary16 half-precision format, the 4-byte format (32-bit) is identical to
93the IEEE 754 binary32 single precision format, and the 8-byte format to the
94IEEE 754 binary64 double precision format, although the packing of INFs and
95NaNs (if such things exist on the platform) isn't handled correctly, and
96attempting to unpack a bytes string containing an IEEE INF or NaN will raise an
97exception.
98
99On non-IEEE platforms with more precision, or larger dynamic range, than IEEE
100754 supports, not all values can be packed; on non-IEEE platforms with less
101precision, or smaller dynamic range, not all values can be unpacked. What
102happens in such cases is partly accidental (alas).
103
104.. versionadded:: 3.11
105
106Pack functions
107--------------
108
109The pack routines write 2, 4 or 8 bytes, starting at *p*. *le* is an
110:c:expr:`int` argument, non-zero if you want the bytes string in little-endian
111format (exponent last, at ``p+1``, ``p+3``, or ``p+6`` ``p+7``), zero if you
112want big-endian format (exponent first, at *p*). The :c:data:`PY_BIG_ENDIAN`
113constant can be used to use the native endian: it is equal to ``1`` on big
114endian processor, or ``0`` on little endian processor.
115
116Return value: ``0`` if all is OK, ``-1`` if error (and an exception is set,
117most likely :exc:`OverflowError`).
118
119There are two problems on non-IEEE platforms:
120
121* What this does is undefined if *x* is a NaN or infinity.
122* ``-0.0`` and ``+0.0`` produce the same bytes string.
123
124.. c:function:: int PyFloat_Pack2(double x, unsigned char *p, int le)
125
126   Pack a C double as the IEEE 754 binary16 half-precision format.
127
128.. c:function:: int PyFloat_Pack4(double x, unsigned char *p, int le)
129
130   Pack a C double as the IEEE 754 binary32 single precision format.
131
132.. c:function:: int PyFloat_Pack8(double x, unsigned char *p, int le)
133
134   Pack a C double as the IEEE 754 binary64 double precision format.
135
136
137Unpack functions
138----------------
139
140The unpack routines read 2, 4 or 8 bytes, starting at *p*.  *le* is an
141:c:expr:`int` argument, non-zero if the bytes string is in little-endian format
142(exponent last, at ``p+1``, ``p+3`` or ``p+6`` and ``p+7``), zero if big-endian
143(exponent first, at *p*). The :c:data:`PY_BIG_ENDIAN` constant can be used to
144use the native endian: it is equal to ``1`` on big endian processor, or ``0``
145on little endian processor.
146
147Return value: The unpacked double.  On error, this is ``-1.0`` and
148:c:func:`PyErr_Occurred` is true (and an exception is set, most likely
149:exc:`OverflowError`).
150
151Note that on a non-IEEE platform this will refuse to unpack a bytes string that
152represents a NaN or infinity.
153
154.. c:function:: double PyFloat_Unpack2(const unsigned char *p, int le)
155
156   Unpack the IEEE 754 binary16 half-precision format as a C double.
157
158.. c:function:: double PyFloat_Unpack4(const unsigned char *p, int le)
159
160   Unpack the IEEE 754 binary32 single precision format as a C double.
161
162.. c:function:: double PyFloat_Unpack8(const unsigned char *p, int le)
163
164   Unpack the IEEE 754 binary64 double precision format as a C double.
165