Python-2.7.3/Python/pymath.c

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 1 #include "Python.h"
 2 
 3 #ifdef X87_DOUBLE_ROUNDING
 4 /* On x86 platforms using an x87 FPU, this function is called from the
 5    Py_FORCE_DOUBLE macro (defined in pymath.h) to force a floating-point
 6    number out of an 80-bit x87 FPU register and into a 64-bit memory location,
 7    thus rounding from extended precision to double precision. */
 8 double _Py_force_double(double x)
 9 {
10     volatile double y;
11     y = x;
12     return y;
13 }
14 #endif
15 
16 #ifdef HAVE_GCC_ASM_FOR_X87
17 
18 /* inline assembly for getting and setting the 387 FPU control word on
19    gcc/x86 */
20 
21 unsigned short _Py_get_387controlword(void) {
22     unsigned short cw;
23     __asm__ __volatile__ ("fnstcw %0" : "=m" (cw));
24     return cw;
25 }
26 
27 void _Py_set_387controlword(unsigned short cw) {
28     __asm__ __volatile__ ("fldcw %0" : : "m" (cw));
29 }
30 
31 #endif
32 
33 
34 #ifndef HAVE_HYPOT
35 double hypot(double x, double y)
36 {
37     double yx;
38 
39     x = fabs(x);
40     y = fabs(y);
41     if (x < y) {
42         double temp = x;
43         x = y;
44         y = temp;
45     }
46     if (x == 0.)
47         return 0.;
48     else {
49         yx = y/x;
50         return x*sqrt(1.+yx*yx);
51     }
52 }
53 #endif /* HAVE_HYPOT */
54 
55 #ifndef HAVE_COPYSIGN
56 double
57 copysign(double x, double y)
58 {
59     /* use atan2 to distinguish -0. from 0. */
60     if (y > 0. || (y == 0. && atan2(y, -1.) > 0.)) {
61         return fabs(x);
62     } else {
63         return -fabs(x);
64     }
65 }
66 #endif /* HAVE_COPYSIGN */
67 
68 #ifndef HAVE_ROUND
69 double
70 round(double x)
71 {
72     double absx, y;
73     absx = fabs(x);
74     y = floor(absx);
75     if (absx - y >= 0.5)
76     y += 1.0;
77     return copysign(y, x);
78 }
79 #endif /* HAVE_ROUND */