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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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GPG key ID: 4AEE18F83AFDEB23
11 changed files with 104 additions and 96 deletions
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65
Include/internal/pycore_pymath.h
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@ -85,19 +85,34 @@ static inline void _Py_ADJUST_ERANGE2(double x, double y)
(_Py_IntegralTypeMin(type) <= v && v <= _Py_IntegralTypeMax(type))
//--- Implementation of the HAVE_PY_SET_53BIT_PRECISION macro -------------
//--- defined in pyport.h -------------------------------------------------
//--- HAVE_PY_SET_53BIT_PRECISION macro ------------------------------------
//
// Give appropriate definitions for the following three macros:
// 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.
//
// _Py_SET_53BIT_PRECISION_HEADER : any variable declarations needed to
// use the two macros below.
// _Py_SET_53BIT_PRECISION_START : store original FPU settings, and
// set FPU to 53-bit precision/round-half-to-even
// _Py_SET_53BIT_PRECISION_END : restore original FPU settings
// 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
//
// and also give appropriate definitions for the following three macros:
//
// * _Py_SET_53BIT_PRECISION_HEADER: any variable declarations needed to
// use the two macros below.
// * _Py_SET_53BIT_PRECISION_START: store original FPU settings, and
// set FPU to 53-bit precision/round-half-to-even
// * _Py_SET_53BIT_PRECISION_END: restore original FPU settings
//
// The macros are designed to be used within a single C function: see
// Python/pystrtod.c for an example of their use.
// Get and set x87 control word for gcc/x86
#ifdef HAVE_GCC_ASM_FOR_X87
#define HAVE_PY_SET_53BIT_PRECISION 1
// Functions defined in Python/pymath.c
extern unsigned short _Py_get_387controlword(void);
@ -124,6 +139,7 @@ extern void _Py_set_387controlword(unsigned short);
// Get and set x87 control word for VisualStudio/x86.
// x87 is not supported in 64-bit or ARM.
#if defined(_MSC_VER) && !defined(_WIN64) && !defined(_M_ARM)
#define HAVE_PY_SET_53BIT_PRECISION 1
#include <float.h> // __control87_2()
@ -150,7 +166,10 @@ extern void _Py_set_387controlword(unsigned short);
} while (0)
#endif
// MC68881
#ifdef HAVE_GCC_ASM_FOR_MC68881
#define HAVE_PY_SET_53BIT_PRECISION 1
#define _Py_SET_53BIT_PRECISION_HEADER \
unsigned int old_fpcr, new_fpcr
#define _Py_SET_53BIT_PRECISION_START \
@ -178,6 +197,36 @@ extern void _Py_set_387controlword(unsigned short);
#endif
//--- _PY_SHORT_FLOAT_REPR macro -------------------------------------------
// 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 significant 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_SHORT_FLOAT_REPR 0
#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_SHORT_FLOAT_REPR 0
#endif
#ifndef _PY_SHORT_FLOAT_REPR
# define _PY_SHORT_FLOAT_REPR 1
#endif
#ifdef __cplusplus
}
#endif