1 #ifndef Py_INTERNAL_PYMATH_H
2 #define Py_INTERNAL_PYMATH_H
3 #ifdef __cplusplus
4 extern "C" {
5 #endif
6
7 #ifndef Py_BUILD_CORE
8 # error "this header requires Py_BUILD_CORE define"
9 #endif
10
11
12 /* _Py_ADJUST_ERANGE1(x)
13 * _Py_ADJUST_ERANGE2(x, y)
14 * Set errno to 0 before calling a libm function, and invoke one of these
15 * macros after, passing the function result(s) (_Py_ADJUST_ERANGE2 is useful
16 * for functions returning complex results). This makes two kinds of
17 * adjustments to errno: (A) If it looks like the platform libm set
18 * errno=ERANGE due to underflow, clear errno. (B) If it looks like the
19 * platform libm overflowed but didn't set errno, force errno to ERANGE. In
20 * effect, we're trying to force a useful implementation of C89 errno
21 * behavior.
22 * Caution:
23 * This isn't reliable. C99 no longer requires libm to set errno under
24 * any exceptional condition, but does require +- HUGE_VAL return
25 * values on overflow. A 754 box *probably* maps HUGE_VAL to a
26 * double infinity, and we're cool if that's so, unless the input
27 * was an infinity and an infinity is the expected result. A C89
28 * system sets errno to ERANGE, so we check for that too. We're
29 * out of luck if a C99 754 box doesn't map HUGE_VAL to +Inf, or
30 * if the returned result is a NaN, or if a C89 box returns HUGE_VAL
31 * in non-overflow cases.
32 */
_Py_ADJUST_ERANGE1(double x)33 static inline void _Py_ADJUST_ERANGE1(double x)
34 {
35 if (errno == 0) {
36 if (x == Py_HUGE_VAL || x == -Py_HUGE_VAL) {
37 errno = ERANGE;
38 }
39 }
40 else if (errno == ERANGE && x == 0.0) {
41 errno = 0;
42 }
43 }
44
_Py_ADJUST_ERANGE2(double x,double y)45 static inline void _Py_ADJUST_ERANGE2(double x, double y)
46 {
47 if (x == Py_HUGE_VAL || x == -Py_HUGE_VAL ||
48 y == Py_HUGE_VAL || y == -Py_HUGE_VAL)
49 {
50 if (errno == 0) {
51 errno = ERANGE;
52 }
53 }
54 else if (errno == ERANGE) {
55 errno = 0;
56 }
57 }
58
59
60 //--- HAVE_PY_SET_53BIT_PRECISION macro ------------------------------------
61 //
62 // The functions _Py_dg_strtod() and _Py_dg_dtoa() in Python/dtoa.c (which are
63 // required to support the short float repr introduced in Python 3.1) require
64 // that the floating-point unit that's being used for arithmetic operations on
65 // C doubles is set to use 53-bit precision. It also requires that the FPU
66 // rounding mode is round-half-to-even, but that's less often an issue.
67 //
68 // If your FPU isn't already set to 53-bit precision/round-half-to-even, and
69 // you want to make use of _Py_dg_strtod() and _Py_dg_dtoa(), then you should:
70 //
71 // #define HAVE_PY_SET_53BIT_PRECISION 1
72 //
73 // and also give appropriate definitions for the following three macros:
74 //
75 // * _Py_SET_53BIT_PRECISION_HEADER: any variable declarations needed to
76 // use the two macros below.
77 // * _Py_SET_53BIT_PRECISION_START: store original FPU settings, and
78 // set FPU to 53-bit precision/round-half-to-even
79 // * _Py_SET_53BIT_PRECISION_END: restore original FPU settings
80 //
81 // The macros are designed to be used within a single C function: see
82 // Python/pystrtod.c for an example of their use.
83
84
85 // Get and set x87 control word for gcc/x86
86 #ifdef HAVE_GCC_ASM_FOR_X87
87 #define HAVE_PY_SET_53BIT_PRECISION 1
88
89 // Functions defined in Python/pymath.c
90 extern unsigned short _Py_get_387controlword(void);
91 extern void _Py_set_387controlword(unsigned short);
92
93 #define _Py_SET_53BIT_PRECISION_HEADER \
94 unsigned short old_387controlword, new_387controlword
95 #define _Py_SET_53BIT_PRECISION_START \
96 do { \
97 old_387controlword = _Py_get_387controlword(); \
98 new_387controlword = (old_387controlword & ~0x0f00) | 0x0200; \
99 if (new_387controlword != old_387controlword) { \
100 _Py_set_387controlword(new_387controlword); \
101 } \
102 } while (0)
103 #define _Py_SET_53BIT_PRECISION_END \
104 do { \
105 if (new_387controlword != old_387controlword) { \
106 _Py_set_387controlword(old_387controlword); \
107 } \
108 } while (0)
109 #endif
110
111 // Get and set x87 control word for VisualStudio/x86.
112 // x87 is not supported in 64-bit or ARM.
113 #if defined(_MSC_VER) && !defined(_WIN64) && !defined(_M_ARM)
114 #define HAVE_PY_SET_53BIT_PRECISION 1
115
116 #include <float.h> // __control87_2()
117
118 #define _Py_SET_53BIT_PRECISION_HEADER \
119 unsigned int old_387controlword, new_387controlword, out_387controlword
120 // We use the __control87_2 function to set only the x87 control word.
121 // The SSE control word is unaffected.
122 #define _Py_SET_53BIT_PRECISION_START \
123 do { \
124 __control87_2(0, 0, &old_387controlword, NULL); \
125 new_387controlword = \
126 (old_387controlword & ~(_MCW_PC | _MCW_RC)) | (_PC_53 | _RC_NEAR); \
127 if (new_387controlword != old_387controlword) { \
128 __control87_2(new_387controlword, _MCW_PC | _MCW_RC, \
129 &out_387controlword, NULL); \
130 } \
131 } while (0)
132 #define _Py_SET_53BIT_PRECISION_END \
133 do { \
134 if (new_387controlword != old_387controlword) { \
135 __control87_2(old_387controlword, _MCW_PC | _MCW_RC, \
136 &out_387controlword, NULL); \
137 } \
138 } while (0)
139 #endif
140
141
142 // MC68881
143 #ifdef HAVE_GCC_ASM_FOR_MC68881
144 #define HAVE_PY_SET_53BIT_PRECISION 1
145 #define _Py_SET_53BIT_PRECISION_HEADER \
146 unsigned int old_fpcr, new_fpcr
147 #define _Py_SET_53BIT_PRECISION_START \
148 do { \
149 __asm__ ("fmove.l %%fpcr,%0" : "=g" (old_fpcr)); \
150 /* Set double precision / round to nearest. */ \
151 new_fpcr = (old_fpcr & ~0xf0) | 0x80; \
152 if (new_fpcr != old_fpcr) { \
153 __asm__ volatile ("fmove.l %0,%%fpcr" : : "g" (new_fpcr));\
154 } \
155 } while (0)
156 #define _Py_SET_53BIT_PRECISION_END \
157 do { \
158 if (new_fpcr != old_fpcr) { \
159 __asm__ volatile ("fmove.l %0,%%fpcr" : : "g" (old_fpcr)); \
160 } \
161 } while (0)
162 #endif
163
164 // Default definitions are empty
165 #ifndef _Py_SET_53BIT_PRECISION_HEADER
166 # define _Py_SET_53BIT_PRECISION_HEADER
167 # define _Py_SET_53BIT_PRECISION_START
168 # define _Py_SET_53BIT_PRECISION_END
169 #endif
170
171
172 //--- _PY_SHORT_FLOAT_REPR macro -------------------------------------------
173
174 // If we can't guarantee 53-bit precision, don't use the code
175 // in Python/dtoa.c, but fall back to standard code. This
176 // means that repr of a float will be long (17 significant digits).
177 //
178 // Realistically, there are two things that could go wrong:
179 //
180 // (1) doubles aren't IEEE 754 doubles, or
181 // (2) we're on x86 with the rounding precision set to 64-bits
182 // (extended precision), and we don't know how to change
183 // the rounding precision.
184 #if !defined(DOUBLE_IS_LITTLE_ENDIAN_IEEE754) && \
185 !defined(DOUBLE_IS_BIG_ENDIAN_IEEE754) && \
186 !defined(DOUBLE_IS_ARM_MIXED_ENDIAN_IEEE754)
187 # define _PY_SHORT_FLOAT_REPR 0
188 #endif
189
190 // Double rounding is symptomatic of use of extended precision on x86.
191 // If we're seeing double rounding, and we don't have any mechanism available
192 // for changing the FPU rounding precision, then don't use Python/dtoa.c.
193 #if defined(X87_DOUBLE_ROUNDING) && !defined(HAVE_PY_SET_53BIT_PRECISION)
194 # define _PY_SHORT_FLOAT_REPR 0
195 #endif
196
197 #ifndef _PY_SHORT_FLOAT_REPR
198 # define _PY_SHORT_FLOAT_REPR 1
199 #endif
200
201
202 #ifdef __cplusplus
203 }
204 #endif
205 #endif /* !Py_INTERNAL_PYMATH_H */
206