Floating Point Objects
**********************

type PyFloatObject

   This subtype of "PyObject" represents a Python floating point
   object.

PyTypeObject PyFloat_Type
    * 次に属します: Stable ABI.*

   This instance of "PyTypeObject" represents the Python floating
   point type.  This is the same object as "float" in the Python
   layer.

int PyFloat_Check(PyObject *p)

   引数が "PyFloatObject" か "PyFloatObject" のサブタイプであるときに
   真を返します。この関数は常に成功します。

int PyFloat_CheckExact(PyObject *p)

   引数が "PyFloatObject" であるが "PyFloatObject" のサブタイプでない
   ときに真を返します。この関数は常に成功します。

PyObject *PyFloat_FromString(PyObject *str)
    *戻り値: 新しい参照。** 次に属します: Stable ABI.*

   *str* の文字列値をもとに "PyFloatObject" オブジェクトを生成します。
   失敗すると "NULL" を返します。

PyObject *PyFloat_FromDouble(double v)
    *戻り値: 新しい参照。** 次に属します: Stable ABI.*

   *v* から "PyFloatObject" オブジェクトを生成して返します。 失敗する
   と "NULL" を返します。

double PyFloat_AsDouble(PyObject *pyfloat)
    * 次に属します: Stable ABI.*

   Return a C double representation of the contents of *pyfloat*.  If
   *pyfloat* is not a Python floating point object but has a
   "__float__()" method, this method will first be called to convert
   *pyfloat* into a float. If "__float__()" is not defined then it
   falls back to "__index__()". This method returns "-1.0" upon
   failure, so one should call "PyErr_Occurred()" to check for errors.

   バージョン 3.8 で変更: 可能であれば "__index__()" を使うようになり
   ました。

double PyFloat_AS_DOUBLE(PyObject *pyfloat)

   *pyfloat* の指す値を、 C の double 型表現で返しますが、エラーチェッ
   クを行いません。

PyObject *PyFloat_GetInfo(void)
    *戻り値: 新しい参照。** 次に属します: Stable ABI.*

   float の精度、最小値、最大値に関する情報を含む structseq インスタン
   スを返します。これは、 "float.h" ファイルの薄いラッパーです。

double PyFloat_GetMax()
    * 次に属します: Stable ABI.*

   float の表現できる最大限解値 *DBL_MAX* を C の double 型で返します
   。

double PyFloat_GetMin()
    * 次に属します: Stable ABI.*

   float の正規化された最小の正の値 *DBL_MIN* を C の double 型で返し
   ます。


Pack and Unpack functions
=========================

The pack and unpack functions provide an efficient platform-
independent way to store floating-point values as byte strings. The
Pack routines produce a bytes string from a C double, and the Unpack
routines produce a C double from such a bytes string. The suffix (2, 4
or 8) specifies the number of bytes in the bytes string.

On platforms that appear to use IEEE 754 formats these functions work
by copying bits. On other platforms, the 2-byte format is identical to
the IEEE 754 binary16 half-precision format, the 4-byte format
(32-bit) is identical to the IEEE 754 binary32 single precision
format, and the 8-byte format to the IEEE 754 binary64 double
precision format, although the packing of INFs and NaNs (if such
things exist on the platform) isn't handled correctly, and attempting
to unpack a bytes string containing an IEEE INF or NaN will raise an
exception.

On non-IEEE platforms with more precision, or larger dynamic range,
than IEEE 754 supports, not all values can be packed; on non-IEEE
platforms with less precision, or smaller dynamic range, not all
values can be unpacked. What happens in such cases is partly
accidental (alas).

バージョン 3.11 で追加.


Pack functions
--------------

The pack routines write 2, 4 or 8 bytes, starting at *p*. *le* is an
int argument, non-zero if you want the bytes string in little-endian
format (exponent last, at "p+1", "p+3", or "p+6" "p+7"), zero if you
want big-endian format (exponent first, at *p*). The "PY_BIG_ENDIAN"
constant can be used to use the native endian: it is equal to "1" on
big endian processor, or "0" on little endian processor.

Return value: "0" if all is OK, "-1" if error (and an exception is
set, most likely "OverflowError").

There are two problems on non-IEEE platforms:

* What this does is undefined if *x* is a NaN or infinity.

* "-0.0" and "+0.0" produce the same bytes string.

int PyFloat_Pack2(double x, unsigned char *p, int le)

   Pack a C double as the IEEE 754 binary16 half-precision format.

int PyFloat_Pack4(double x, unsigned char *p, int le)

   Pack a C double as the IEEE 754 binary32 single precision format.

int PyFloat_Pack8(double x, unsigned char *p, int le)

   Pack a C double as the IEEE 754 binary64 double precision format.


Unpack functions
----------------

The unpack routines read 2, 4 or 8 bytes, starting at *p*.  *le* is an
int argument, non-zero if the bytes string is in little-endian format
(exponent last, at "p+1", "p+3" or "p+6" and "p+7"), zero if big-
endian (exponent first, at *p*). The "PY_BIG_ENDIAN" constant can be
used to use the native endian: it is equal to "1" on big endian
processor, or "0" on little endian processor.

Return value: The unpacked double.  On error, this is "-1.0" and
"PyErr_Occurred()" is true (and an exception is set, most likely
"OverflowError").

Note that on a non-IEEE platform this will refuse to unpack a bytes
string that represents a NaN or infinity.

double PyFloat_Unpack2(const unsigned char *p, int le)

   Unpack the IEEE 754 binary16 half-precision format as a C double.

double PyFloat_Unpack4(const unsigned char *p, int le)

   Unpack the IEEE 754 binary32 single precision format as a C double.

double PyFloat_Unpack8(const unsigned char *p, int le)

   Unpack the IEEE 754 binary64 double precision format as a C double.
