circuitpython/lib/libm_dbl/trunc.c

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#include "libm.h"
double trunc(double x)
{
union {double f; uint64_t i;} u = {x};
int e = (int)(u.i >> 52 & 0x7ff) - 0x3ff + 12;
uint64_t m;
if (e >= 52 + 12)
return x;
if (e < 12)
e = 1;
m = -1ULL >> e;
if ((u.i & m) == 0)
return x;
FORCE_EVAL(x + 0x1p120f);
u.i &= ~m;
return u.f;
}