mirror of
https://github.com/python/cpython
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ba283e2b7f
[ 1181301 ] make float packing copy bytes when they can
which hasn't been reviewed, despite numerous threats to check it in
anyway if noone reviews it. Please read the diff on the checkin list,
at least!
The basic idea is to examine the bytes of some 'probe values' to see if
the current platform is a IEEE 754-ish platform, and if so
_PyFloat_{Pack,Unpack}{4,8} just copy bytes around.
The rest is hair for testing, and tests.
101 lines
4.1 KiB
C
101 lines
4.1 KiB
C
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/* Float object interface */
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/*
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PyFloatObject represents a (double precision) floating point number.
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*/
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#ifndef Py_FLOATOBJECT_H
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#define Py_FLOATOBJECT_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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typedef struct {
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PyObject_HEAD
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double ob_fval;
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} PyFloatObject;
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PyAPI_DATA(PyTypeObject) PyFloat_Type;
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#define PyFloat_Check(op) PyObject_TypeCheck(op, &PyFloat_Type)
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#define PyFloat_CheckExact(op) ((op)->ob_type == &PyFloat_Type)
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/* Return Python float from string PyObject. Second argument ignored on
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input, and, if non-NULL, NULL is stored into *junk (this tried to serve a
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purpose once but can't be made to work as intended). */
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PyAPI_FUNC(PyObject *) PyFloat_FromString(PyObject*, char** junk);
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/* Return Python float from C double. */
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PyAPI_FUNC(PyObject *) PyFloat_FromDouble(double);
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/* Extract C double from Python float. The macro version trades safety for
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speed. */
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PyAPI_FUNC(double) PyFloat_AsDouble(PyObject *);
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#define PyFloat_AS_DOUBLE(op) (((PyFloatObject *)(op))->ob_fval)
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/* Write repr(v) into the char buffer argument, followed by null byte. The
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buffer must be "big enough"; >= 100 is very safe.
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PyFloat_AsReprString(buf, x) strives to print enough digits so that
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PyFloat_FromString(buf) then reproduces x exactly. */
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PyAPI_FUNC(void) PyFloat_AsReprString(char*, PyFloatObject *v);
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/* Write str(v) into the char buffer argument, followed by null byte. The
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buffer must be "big enough"; >= 100 is very safe. Note that it's
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unusual to be able to get back the float you started with from
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PyFloat_AsString's result -- use PyFloat_AsReprString() if you want to
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preserve precision across conversions. */
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PyAPI_FUNC(void) PyFloat_AsString(char*, PyFloatObject *v);
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/* _PyFloat_{Pack,Unpack}{4,8}
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*
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* The struct and pickle (at least) modules need an efficient platform-
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* independent way to store floating-point values as byte strings.
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* The Pack routines produce a string from a C double, and the Unpack
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* routines produce a C double from such a string. The suffix (4 or 8)
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* specifies the number of bytes in the string.
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*
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* On platforms that appear to use (see _PyFloat_Init()) IEEE-754 formats
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* these functions work by copying bits. On other platforms, the formats the
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* 4- byte format is identical to the IEEE-754 single precision format, and
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* the 8-byte format to the IEEE-754 double precision format, although the
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* packing of INFs and NaNs (if such things exist on the platform) isn't
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* handled correctly, and attempting to unpack a string containing an IEEE
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* INF or NaN will raise an exception.
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*
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* On non-IEEE platforms with more precision, or larger dynamic range, than
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* 754 supports, not all values can be packed; on non-IEEE platforms with less
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* precision, or smaller dynamic range, not all values can be unpacked. What
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* happens in such cases is partly accidental (alas).
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*/
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/* The pack routines write 4 or 8 bytes, starting at p. le is a bool
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* argument, true if you want the string in little-endian format (exponent
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* last, at p+3 or p+7), false if you want big-endian format (exponent
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* first, at p).
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* Return value: 0 if all is OK, -1 if error (and an exception is
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* set, most likely OverflowError).
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* There are two problems on non-IEEE platforms:
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* 1): What this does is undefined if x is a NaN or infinity.
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* 2): -0.0 and +0.0 produce the same string.
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*/
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PyAPI_FUNC(int) _PyFloat_Pack4(double x, unsigned char *p, int le);
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PyAPI_FUNC(int) _PyFloat_Pack8(double x, unsigned char *p, int le);
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/* The unpack routines read 4 or 8 bytes, starting at p. le is a bool
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* argument, true if the string is in little-endian format (exponent
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* last, at p+3 or p+7), false if big-endian (exponent first, at p).
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* Return value: The unpacked double. On error, this is -1.0 and
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* PyErr_Occurred() is true (and an exception is set, most likely
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* OverflowError). Note that on a non-IEEE platform this will refuse
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* to unpack a string that represents a NaN or infinity.
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*/
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PyAPI_FUNC(double) _PyFloat_Unpack4(const unsigned char *p, int le);
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PyAPI_FUNC(double) _PyFloat_Unpack8(const unsigned char *p, int le);
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#ifdef __cplusplus
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}
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#endif
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#endif /* !Py_FLOATOBJECT_H */
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