cpython/Python/pymath.c
Niklas Fiekas 794e7d1ab2
bpo-29782: Consolidate _Py_Bit_Length() (GH-20739)
In GH-2866, _Py_Bit_Length() was added to pymath.h for lack of a better
location. GH-20518 added a more appropriate header file for bit utilities. It
also shows how to properly use intrinsics. This allows reconsidering bpo-29782.

* Move the function to the new header.
* Changed return type to match __builtin_clzl() and reviewed usage.
* Use intrinsics where available.
* Pick a fallback implementation suitable for inlining.
2020-06-15 14:33:48 +02:00

82 lines
1.6 KiB
C

#include "Python.h"
#ifdef X87_DOUBLE_ROUNDING
/* On x86 platforms using an x87 FPU, this function is called from the
Py_FORCE_DOUBLE macro (defined in pymath.h) to force a floating-point
number out of an 80-bit x87 FPU register and into a 64-bit memory location,
thus rounding from extended precision to double precision. */
double _Py_force_double(double x)
{
volatile double y;
y = x;
return y;
}
#endif
#ifdef HAVE_GCC_ASM_FOR_X87
/* inline assembly for getting and setting the 387 FPU control word on
gcc/x86 */
#ifdef _Py_MEMORY_SANITIZER
__attribute__((no_sanitize_memory))
#endif
unsigned short _Py_get_387controlword(void) {
unsigned short cw;
__asm__ __volatile__ ("fnstcw %0" : "=m" (cw));
return cw;
}
void _Py_set_387controlword(unsigned short cw) {
__asm__ __volatile__ ("fldcw %0" : : "m" (cw));
}
#endif
#ifndef HAVE_HYPOT
double hypot(double x, double y)
{
double yx;
x = fabs(x);
y = fabs(y);
if (x < y) {
double temp = x;
x = y;
y = temp;
}
if (x == 0.)
return 0.;
else {
yx = y/x;
return x*sqrt(1.+yx*yx);
}
}
#endif /* HAVE_HYPOT */
#ifndef HAVE_COPYSIGN
double
copysign(double x, double y)
{
/* use atan2 to distinguish -0. from 0. */
if (y > 0. || (y == 0. && atan2(y, -1.) > 0.)) {
return fabs(x);
} else {
return -fabs(x);
}
}
#endif /* HAVE_COPYSIGN */
#ifndef HAVE_ROUND
double
round(double x)
{
double absx, y;
absx = fabs(x);
y = floor(absx);
if (absx - y >= 0.5)
y += 1.0;
return copysign(y, x);
}
#endif /* HAVE_ROUND */