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author | Mark Dickinson <dickinsm@gmail.com> | 2009-10-24 13:28:38 (GMT) |
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committer | Mark Dickinson <dickinsm@gmail.com> | 2009-10-24 13:28:38 (GMT) |
commit | 1d6e2e1833864238b903325b37d05fef9b794393 (patch) | |
tree | 9ec5c642e19d7aacf9be92a08d28b9434f99b4f6 /Include | |
parent | 5e9f6676eaf911c9218549ea5f1e022f1ea95e32 (diff) | |
download | cpython-1d6e2e1833864238b903325b37d05fef9b794393.zip cpython-1d6e2e1833864238b903325b37d05fef9b794393.tar.gz cpython-1d6e2e1833864238b903325b37d05fef9b794393.tar.bz2 |
Issue #7117 (backport py3k float repr) continued:
- add double endianness detection to configure script
- add configure-time check to see whether we can use inline
assembly to get and set x87 control word in configure script
- add functions to get and set x87 control word in Python/pymath.c
- add pyport.h logic to determine whether it's safe to use the
short float repr or not
Diffstat (limited to 'Include')
-rw-r--r-- | Include/pymacconfig.h | 6 | ||||
-rw-r--r-- | Include/pymath.h | 5 | ||||
-rw-r--r-- | Include/pyport.h | 74 |
3 files changed, 85 insertions, 0 deletions
diff --git a/Include/pymacconfig.h b/Include/pymacconfig.h index b2cc0b7..3a3428c 100644 --- a/Include/pymacconfig.h +++ b/Include/pymacconfig.h @@ -17,6 +17,9 @@ # undef SIZEOF_VOID_P # undef SIZEOF__BOOL # undef WORDS_BIGENDIAN +# undef DOUBLE_IS_ARM_MIXED_ENDIAN_IEEE754 +# undef DOUBLE_IS_BIG_ENDIAN_IEEE754 +# undef DOUBLE_IS_LITTLE_ENDIAN_IEEE754 # undef VA_LIST_IS_ARRAY # if defined(__LP64__) && defined(__x86_64__) @@ -65,6 +68,9 @@ #ifdef __BIG_ENDIAN__ #define WORDS_BIGENDIAN 1 +#define DOUBLE_IS_BIG_ENDIAN_IEEE754 +#else +#define DOUBLE_IS_LITTLE_ENDIAN_IEEE754 #endif /* __BIG_ENDIAN */ /* diff --git a/Include/pymath.h b/Include/pymath.h index 7623efa..dc2c427 100644 --- a/Include/pymath.h +++ b/Include/pymath.h @@ -92,6 +92,11 @@ PyAPI_FUNC(double) _Py_force_double(double); # endif #endif +#ifdef HAVE_GCC_ASM_FOR_X87 +PyAPI_FUNC(unsigned short) _Py_get_387controlword(void); +PyAPI_FUNC(void) _Py_set_387controlword(unsigned short); +#endif + /* Py_IS_NAN(X) * Return 1 if float or double arg is a NaN, else 0. * Caution: diff --git a/Include/pyport.h b/Include/pyport.h index da83196..62d4524 100644 --- a/Include/pyport.h +++ b/Include/pyport.h @@ -488,6 +488,80 @@ extern "C" { errno = 0; \ } while(0) +/* 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 + * + * and also give appropriate definitions for the following three macros: + * + * _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 + * _PY_SET_53BIT_PRECISION_HEADER : any variable declarations needed to + * use the two macros above. + * + * 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 +/* _Py_get/set_387controlword functions are defined in Python/pymath.c */ +#define _Py_SET_53BIT_PRECISION_HEADER \ + unsigned short old_387controlword, new_387controlword +#define _Py_SET_53BIT_PRECISION_START \ + do { \ + old_387controlword = _Py_get_387controlword(); \ + new_387controlword = (old_387controlword & ~0x0f00) | 0x0200; \ + if (new_387controlword != old_387controlword) \ + _Py_set_387controlword(new_387controlword); \ + } while (0) +#define _Py_SET_53BIT_PRECISION_END \ + if (new_387controlword != old_387controlword) \ + _Py_set_387controlword(old_387controlword) +#endif + +/* default definitions are empty */ +#ifndef HAVE_PY_SET_53BIT_PRECISION +#define _Py_SET_53BIT_PRECISION_HEADER +#define _Py_SET_53BIT_PRECISION_START +#define _Py_SET_53BIT_PRECISION_END +#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. * Usage: |