# 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。

Py_INFINITY

  This macro expands to a constant expression of type double, that represents the positive infinity.

  It is equivalent to the `INFINITY` macro from the C11 standard `<math.h>` header.

  Soft deprecated since version 3.15.

Py_NAN

  This macro expands to a constant expression of type double, that represents a quiet not-a-number (qNaN) value.

  On most platforms, this is equivalent to the `NAN` macro from the C11 standard `<math.h>` header.

Py_HUGE_VAL

  Equivalent to `INFINITY`.

  Soft deprecated since version 3.14.

Py_MATH_E

  The definition (accurate for a double type) of the `math.e` constant.

Py_MATH_El

  High precision (long double) definition of `e` constant.

  バージョン 3.15 で非推奨、バージョン 3.20 で削除予定.

Py_MATH_PI

  The definition (accurate for a double type) of the `math.pi` constant.

Py_MATH_PIl

  High precision (long double) definition of `pi` constant.

  バージョン 3.15 で非推奨、バージョン 3.20 で削除予定.

Py_MATH_TAU

  The definition (accurate for a double type) of the `math.tau` constant.

  Added in version 3.6.

Py_RETURN_NAN

  Return `math.nan` from a function.

  On most platforms, this is equivalent to `return PyFloat_FromDouble(NAN)`.

Py_RETURN_INF(sign)

  Return `math.inf` or `-math.inf` from a function, depending on the sign of sign.

  On most platforms, this is equivalent to the following:

      return PyFloat_FromDouble(copysign(INFINITY, sign));

Py_IS_FINITE(X)

  Return `1` if the given floating-point number X is finite, that is, it is normal, subnormal or zero, but not infinite or NaN. Return `0` otherwise.

  Soft deprecated since version 3.14: Use `isfinite` instead.

Py_IS_INFINITY(X)

  Return `1` if the given floating-point number X is positive or negative infinity. Return `0` otherwise.

  Soft deprecated since version 3.14: Use `isinf` instead.

Py_IS_NAN(X)

  Return `1` if the given floating-point number X is a not-a-number (NaN) value. Return `0` otherwise.

  Soft deprecated since version 3.14: Use `isnan` instead.

## 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:

- The 2-byte format is the IEEE 754 binary16 half-precision format.

- The 4-byte format is the IEEE 754 binary32 single-precision format.

- The 8-byte format is the IEEE 754 binary64 double-precision format.

The NaN type may not be preserved on some platforms while unpacking (signaling NaNs become quiet NaNs), for example on x86 systems in 32-bit mode.

It's assumed that the double type has the IEEE 754 binary64 double precision format. What happens if it's not true is partly accidental (alas). 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. The packing of special numbers like INFs and NaNs (if such things exist on the platform) may not be handled correctly, and attempting to unpack a bytes string containing an IEEE INF or NaN may raise an exception.

Added in version 3.11.

### 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` and `p+7`), zero if you want big-endian format (exponent first, at p). Use the `PY_LITTLE_ENDIAN` constant to select the native endian: it is equal to `0` on big endian processor, or `1` on little endian processor.

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

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

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

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

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

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

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

  CPython 実装の詳細: This function always succeeds in CPython.

### 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). Use the `PY_LITTLE_ENDIAN` constant to select the native endian: it is equal to `0` on big endian processor, or `1` 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`).

CPython 実装の詳細: These functions always succeed in CPython.

double PyFloat_Unpack2(const char *p, int le)

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

double PyFloat_Unpack4(const char *p, int le)

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

double PyFloat_Unpack8(const char *p, int le)

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