1 /* @(#)s_scalbn.c 5.1 93/09/24 */ 2 /* 3 * ==================================================== 4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5 * 6 * Developed at SunPro, a Sun Microsystems, Inc. business. 7 * Permission to use, copy, modify, and distribute this 8 * software is freely granted, provided that this notice 9 * is preserved. 10 * ==================================================== 11 */ 12 13 #include <sys/cdefs.h> 14 #if defined(LIBM_SCCS) && !defined(lint) 15 __RCSID("$NetBSD: s_scalbn.c,v 1.9 1997/10/09 11:33:15 lukem Exp $"); 16 #endif 17 18 /* 19 * scalbn (double x, int n) 20 * scalbn(x,n) returns x* 2**n computed by exponent 21 * manipulation rather than by actually performing an 22 * exponentiation or a multiplication. 23 */ 24 25 #include "math.h" 26 #include "math_private.h" 27 28 #ifdef __STDC__ 29 static const double 30 #else 31 static double 32 #endif 33 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 34 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ 35 huge = 1.0e+300, 36 tiny = 1.0e-300; 37 38 #ifdef __STDC__ 39 double scalbn (double x, int n) 40 #else 41 double scalbn (x,n) 42 double x; int n; 43 #endif 44 { 45 int32_t k,hx,lx; 46 EXTRACT_WORDS(hx,lx,x); 47 k = (hx&0x7ff00000)>>20; /* extract exponent */ 48 if (k==0) { /* 0 or subnormal x */ 49 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ 50 x *= two54; 51 GET_HIGH_WORD(hx,x); 52 k = ((hx&0x7ff00000)>>20) - 54; 53 if (n< -50000) return tiny*x; /*underflow*/ 54 } 55 if (k==0x7ff) return x+x; /* NaN or Inf */ 56 k = k+n; 57 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */ 58 if (k > 0) /* normal result */ 59 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} 60 if (k <= -54) 61 if (n > 50000) /* in case integer overflow in n+k */ 62 return huge*copysign(huge,x); /*overflow*/ 63 else return tiny*copysign(tiny,x); /*underflow*/ 64 k += 54; /* subnormal result */ 65 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); 66 return x*twom54; 67 } 68