bpo-46906: Add PyFloat_Pack8() to the C API (GH-31657)

Add new functions to pack and unpack C double (serialize and
deserialize):

* PyFloat_Pack2(), PyFloat_Pack4(), PyFloat_Pack8()
* PyFloat_Unpack2(), PyFloat_Unpack4(), PyFloat_Unpack8()

Document these functions and add unit tests.

Rename private functions and move them from the internal C API
to the public C API:

* _PyFloat_Pack2() => PyFloat_Pack2()
* _PyFloat_Pack4() => PyFloat_Pack4()
* _PyFloat_Pack8() => PyFloat_Pack8()
* _PyFloat_Unpack2() => PyFloat_Unpack2()
* _PyFloat_Unpack4() => PyFloat_Unpack4()
* _PyFloat_Unpack8() => PyFloat_Unpack8()

Replace the "unsigned char*" type with "char*" which is more common
and easy to use.

2 files changed, 9 insertions, 48 deletions

diff --git a/Include/cpython/floatobject.h b/Include/cpython/floatobject.h
index fffd468..7795d9f 100644
--- a/Include/cpython/floatobject.h
+++ b/Include/cpython/floatobject.h
@@ -10,3 +10,12 @@ typedef struct {
 // Macro version of PyFloat_AsDouble() trading safety for speed.
 // It doesn't check if op is a double object.
 #define PyFloat_AS_DOUBLE(op) (((PyFloatObject *)(op))->ob_fval)
+
+
+PyAPI_FUNC(int) PyFloat_Pack2(double x, char *p, int le);
+PyAPI_FUNC(int) PyFloat_Pack4(double x, char *p, int le);
+PyAPI_FUNC(int) PyFloat_Pack8(double x, char *p, int le);
+
+PyAPI_FUNC(double) PyFloat_Unpack2(const char *p, int le);
+PyAPI_FUNC(double) PyFloat_Unpack4(const char *p, int le);
+PyAPI_FUNC(double) PyFloat_Unpack8(const char *p, int le);
diff --git a/Include/internal/pycore_floatobject.h b/Include/internal/pycore_floatobject.h
index 891e422..a099f2e 100644
--- a/Include/internal/pycore_floatobject.h
+++ b/Include/internal/pycore_floatobject.h
@@ -38,54 +38,6 @@ struct _Py_float_state {
 #endif
 };
 
-/* _PyFloat_{Pack,Unpack}{4,8}
- *
- * The struct and pickle (at least) modules need an efficient platform-
- * independent way to store floating-point values as byte strings.
- * The Pack routines produce a string from a C double, and the Unpack
- * routines produce a C double from such a string.  The suffix (4 or 8)
- * specifies the number of bytes in the string.
- *
- * On platforms that appear to use (see _PyFloat_Init()) IEEE-754 formats
- * these functions work by copying bits.  On other platforms, the formats the
- * 4- byte format is identical to the IEEE-754 single precision format, and
- * the 8-byte format to the IEEE-754 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 string containing an IEEE
- * INF or NaN will raise an exception.
- *
- * On non-IEEE platforms with more precision, or larger dynamic range, than
- * 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).
- */
-
-/* The pack routines write 2, 4 or 8 bytes, starting at p.  le is a bool
- * argument, true if you want the string in little-endian format (exponent
- * last, at p+1, p+3 or p+7), false if you want big-endian format (exponent
- * first, at p).
- * 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:
- * 1):  What this does is undefined if x is a NaN or infinity.
- * 2):  -0.0 and +0.0 produce the same string.
- */
-PyAPI_FUNC(int) _PyFloat_Pack2(double x, unsigned char *p, int le);
-PyAPI_FUNC(int) _PyFloat_Pack4(double x, unsigned char *p, int le);
-PyAPI_FUNC(int) _PyFloat_Pack8(double x, unsigned char *p, int le);
-
-/* The unpack routines read 2, 4 or 8 bytes, starting at p.  le is a bool
- * argument, true if the string is in little-endian format (exponent
- * last, at p+1, p+3 or p+7), false if big-endian (exponent first, at p).
- * 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 string that represents a NaN or infinity.
- */
-PyAPI_FUNC(double) _PyFloat_Unpack2(const unsigned char *p, int le);
-PyAPI_FUNC(double) _PyFloat_Unpack4(const unsigned char *p, int le);
-PyAPI_FUNC(double) _PyFloat_Unpack8(const unsigned char *p, int le);
-
 
 PyAPI_FUNC(void) _PyFloat_DebugMallocStats(FILE* out);