diff options
| -rw-r--r-- | Misc/NEWS | 37 |
1 files changed, 33 insertions, 4 deletions
@@ -15,11 +15,40 @@ Core and Builtins - Issue #7085: Fix crash when importing some extensions in a thread on MacOSX 10.6. +- Issue #7117: repr(x) for a float x returns a result based on the + shortest decimal string that's guaranteed to round back to x under + correct rounding (with round-half-to-even rounding mode). + Previously it gave a string based on rounding x to 17 decimal digits. + repr(x) for a complex number behaves similarly. On platforms where + the correctly-rounded strtod and dtoa code is not supported (see below), + repr is unchanged. + +- Issue #7117: On almost all platforms: float-to-string and + string-to-float conversions within Python are now correctly rounded. + Places these conversions occur include: str for floats and complex + numbers; the float and complex constructors; old-style and new-style + numeric formatting; serialization and deserialization of floats and + complex numbers using marshal, pickle and json; parsing of float and + imaginary literals in Python code; Decimal-to-float conversion. + + The conversions use a Python-adapted version of David Gay's + well-known dtoa.c, providing correctly-rounded strtod and dtoa C + functions. This code is supported on Windows, and on Unix-like + platforms using gcc, icc or suncc as the C compiler. There may be a + small number of platforms on which correct operation of this code + cannot be guaranteed, so the code is not used: notably, this applies + to platforms where the C double format is not IEEE 754 binary64, and + to platforms on x86 hardware where the x87 FPU is set to 64-bit + precision and Python's configure script is unable to determine how + to change the FPU precision. On these platforms conversions use the + platform strtod and dtoa, as before. + - Issue #7117: Backport round implementation from Python 3.x. round - now uses David Gay's correctly-rounded string <-> double conversions - (when available), and so produces correctly rounded results. There - are two related small changes: (1) round now accepts any class with - an __index__ method for its second argument (but no longer accepts + now uses the correctly-rounded string <-> float conversions + described above (when available), and so produces correctly rounded + results that will display nicely under the float repr. There are + two related small changes: (1) round now accepts any class with an + __index__ method for its second argument (but no longer accepts floats for the second argument), and (2) an excessively large second integer argument (e.g., round(1.234, 10**100)) no longer raises an exception. |