1 2 /* @(#)s_scalbn.c 1.3 95/01/18 */ 3 /* 4 * ==================================================== 5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 6 * 7 * Developed at SunSoft, a Sun Microsystems, Inc. business. 8 * Permission to use, copy, modify, and distribute this 9 * software is freely granted, provided that this notice 10 * is preserved. 11 * ==================================================== 12 */ 13 14 /* 15 * ieee_scalbn (double x, int n) 16 * ieee_scalbn(x,n) returns x* 2**n computed by exponent 17 * manipulation rather than by actually performing an 18 * exponentiation or a multiplication. 19 */ 20 21 #include "fdlibm.h" 22 23 #ifdef __STDC__ 24 static const double 25 #else 26 static double 27 #endif 28 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 29 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ 30 huge = 1.0e+300, 31 tiny = 1.0e-300; 32 33 #ifdef __STDC__ ieee_scalbn(double x,int n)34 double ieee_scalbn (double x, int n) 35 #else 36 double ieee_scalbn (x,n) 37 double x; int n; 38 #endif 39 { 40 int k,hx,lx; 41 hx = __HI(x); 42 lx = __LO(x); 43 k = (hx&0x7ff00000)>>20; /* extract exponent */ 44 if (k==0) { /* 0 or subnormal x */ 45 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ 46 x *= two54; 47 hx = __HI(x); 48 k = ((hx&0x7ff00000)>>20) - 54; 49 if (n< -50000) return tiny*x; /*underflow*/ 50 } 51 if (k==0x7ff) return x+x; /* NaN or Inf */ 52 k = k+n; 53 if (k > 0x7fe) return huge*ieee_copysign(huge,x); /* overflow */ 54 if (k > 0) /* normal result */ 55 {__HI(x) = (hx&0x800fffff)|(k<<20); return x;} 56 if (k <= -54) 57 if (n > 50000) /* in case integer overflow in n+k */ 58 return huge*ieee_copysign(huge,x); /*overflow*/ 59 else return tiny*ieee_copysign(tiny,x); /*underflow*/ 60 k += 54; /* subnormal result */ 61 __HI(x) = (hx&0x800fffff)|(k<<20); 62 return x*twom54; 63 } 64