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

double scalbn(double x, int n)
{
        union {double f; uint64_t i;} u;
        double_t y = x;

        if (n > 1023) {
                y *= 0x1p1023;
                n -= 1023;
                if (n > 1023) {
                        y *= 0x1p1023;
                        n -= 1023;
                        if (n > 1023)
                                n = 1023;
                }
        } else if (n < -1022) {
                /* make sure final n < -53 to avoid double
                   rounding in the subnormal range */
                y *= 0x1p-1022 * 0x1p53;
                n += 1022 - 53;
                if (n < -1022) {
                        y *= 0x1p-1022 * 0x1p53;
                        n += 1022 - 53;
                        if (n < -1022)
                                n = -1022;
                }
        }
        u.i = (uint64_t)(0x3ff+n)<<52;
        x = y * u.f;
        return x;
}