fusl/src/math/rint.c

#include <float.h>
#include <math.h>
#include <stdint.h>

#if FLT_EVAL_METHOD == 0 || FLT_EVAL_METHOD == 1
#define EPS DBL_EPSILON
#elif FLT_EVAL_METHOD == 2
#define EPS LDBL_EPSILON
#endif
static const double_t toint = 1 / EPS;

double rint(double x) {
  union {
    double f;
    uint64_t i;
  } u = {x};
  int e = u.i >> 52 & 0x7ff;
  int s = u.i >> 63;
  double_t y;

  if (e >= 0x3ff + 52)
    return x;
  if (s)
    y = x - toint + toint;
  else
    y = x + toint - toint;
  if (y == 0)
    return s ? -0.0 : 0;
  return y;
}