scalbn.c raw

   1  #include <math.h>
   2  #include <stdint.h>
   3  
   4  double scalbn(double x, int n)
   5  {
   6  	union {double f; uint64_t i;} u;
   7  	double_t y = x;
   8  
   9  	if (n > 1023) {
  10  		y *= 0x1p1023;
  11  		n -= 1023;
  12  		if (n > 1023) {
  13  			y *= 0x1p1023;
  14  			n -= 1023;
  15  			if (n > 1023)
  16  				n = 1023;
  17  		}
  18  	} else if (n < -1022) {
  19  		/* make sure final n < -53 to avoid double
  20  		   rounding in the subnormal range */
  21  		y *= 0x1p-1022 * 0x1p53;
  22  		n += 1022 - 53;
  23  		if (n < -1022) {
  24  			y *= 0x1p-1022 * 0x1p53;
  25  			n += 1022 - 53;
  26  			if (n < -1022)
  27  				n = -1022;
  28  		}
  29  	}
  30  	u.i = (uint64_t)(0x3ff+n)<<52;
  31  	x = y * u.f;
  32  	return x;
  33  }
  34