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 * scalbn (double x, int n) 16 * 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 #ifndef _DOUBLE_IS_32BITS 24 25 #ifdef __STDC__ 26 static const double 27 #else 28 static double 29 #endif 30 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 31 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ 32 huge = 1.0e+300, 33 tiny = 1.0e-300; 34 35 #ifdef __STDC__ scalbn(double x,int n)36 double scalbn (double x, int n) 37 #else 38 double scalbn (x,n) 39 double x; int n; 40 #endif 41 { 42 int32_t k,hx,lx; 43 EXTRACT_WORDS(hx,lx,x); 44 k = (hx&0x7ff00000)>>20; /* extract exponent */ 45 if (k==0) { /* 0 or subnormal x */ 46 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ 47 x *= two54; 48 GET_HIGH_WORD(hx,x); 49 k = ((hx&0x7ff00000)>>20) - 54; 50 if (n< -50000) return tiny*x; /*underflow*/ 51 } 52 if (k==0x7ff) return x+x; /* NaN or Inf */ 53 k = k+n; 54 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */ 55 if (k > 0) /* normal result */ 56 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} 57 if (k <= -54) 58 if (n > 50000) /* in case integer overflow in n+k */ 59 return huge*copysign(huge,x); /*overflow*/ 60 else return tiny*copysign(tiny,x); /*underflow*/ 61 k += 54; /* subnormal result */ 62 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); 63 return x*twom54; 64 } 65 #endif /* _DOUBLE_IS_32BITS */ 66