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bpo-45412: Add _PY_SHORT_FLOAT_REPR macro (GH-31171)

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Remove the HAVE_PY_SET_53BIT_PRECISION macro (moved to the internal
C API).

* Move HAVE_PY_SET_53BIT_PRECISION macro to pycore_pymath.h.
* Replace PY_NO_SHORT_FLOAT_REPR macro with _PY_SHORT_FLOAT_REPR
  macro which is always defined. gcc -Wundef emits a warning when
  using _PY_SHORT_FLOAT_REPR but the macro is not defined, if
  pycore_pymath.h include was forgotten.
This commit is contained in:
Victor Stinner 2022-02-23 18:16:23 +01:00 • committed by GitHub
parent 375a56bd40
commit 9bbdde2180
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11 changed files with 104 additions and 96 deletions
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55
Include/pyport.h
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@ -312,61 +312,6 @@ extern "C" {
#define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) (NARROW)(VALUE)
#endif
/* The functions _Py_dg_strtod and _Py_dg_dtoa in Python/dtoa.c (which are
* required to support the short float repr introduced in Python 3.1) require
* that the floating-point unit that's being used for arithmetic operations
* on C doubles is set to use 53-bit precision. It also requires that the
* FPU rounding mode is round-half-to-even, but that's less often an issue.
*
* If your FPU isn't already set to 53-bit precision/round-half-to-even, and
* you want to make use of _Py_dg_strtod and _Py_dg_dtoa, then you should
*
* #define HAVE_PY_SET_53BIT_PRECISION 1
*
* The macros are designed to be used within a single C function: see
* Python/pystrtod.c for an example of their use.
*/
// HAVE_PY_SET_53BIT_PRECISION macro must be kept in sync with pycore_pymath.h
#ifdef HAVE_GCC_ASM_FOR_X87
// Get and set x87 control word for gcc/x86
# define HAVE_PY_SET_53BIT_PRECISION 1
#endif
#if defined(_MSC_VER) && !defined(_WIN64) && !defined(_M_ARM)
// Get and set x87 control word for VisualStudio/x86.
// x87 not supported in 64-bit or ARM.
# define HAVE_PY_SET_53BIT_PRECISION 1
#endif
#ifdef HAVE_GCC_ASM_FOR_MC68881
# define HAVE_PY_SET_53BIT_PRECISION 1
#endif
/* If we can't guarantee 53-bit precision, don't use the code
in Python/dtoa.c, but fall back to standard code. This
means that repr of a float will be long (17 sig digits).
Realistically, there are two things that could go wrong:
(1) doubles aren't IEEE 754 doubles, or
(2) we're on x86 with the rounding precision set to 64-bits
(extended precision), and we don't know how to change
the rounding precision.
*/
#if !defined(DOUBLE_IS_LITTLE_ENDIAN_IEEE754) && \
!defined(DOUBLE_IS_BIG_ENDIAN_IEEE754) && \
!defined(DOUBLE_IS_ARM_MIXED_ENDIAN_IEEE754)
# define PY_NO_SHORT_FLOAT_REPR
#endif
/* double rounding is symptomatic of use of extended precision on x86. If
we're seeing double rounding, and we don't have any mechanism available for
changing the FPU rounding precision, then don't use Python/dtoa.c. */
#if defined(X87_DOUBLE_ROUNDING) && !defined(HAVE_PY_SET_53BIT_PRECISION)
# define PY_NO_SHORT_FLOAT_REPR
#endif
/* Py_DEPRECATED(version)
* Declare a variable, type, or function deprecated.