bpo-46906: Move `_PyFloat_{Pack,Unpack}{4,8}` from internal to cpython by methane · Pull Request #31649 · python/cpython
/* _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);