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 1.16 2013/01/28 06:34:09 matt 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 "namespace.h" 26 #include "math.h" 27 #include "math_private.h" 28 29 #ifndef _LP64 30 __strong_alias(_scalbn, _scalbln) 31 #endif 32 33 #ifndef __HAVE_LONG_DOUBLE 34 __strong_alias(_scalbnl, _scalbn) 35 __strong_alias(_scalblnl, _scalbln) 36 __weak_alias(scalbnl, _scalbnl) 37 __weak_alias(scalblnl, _scalblnl) 38 #endif 39 40 #ifdef __weak_alias 41 __weak_alias(scalbn, _scalbn) 42 __weak_alias(scalbln, _scalbln) 43 #endif 44 45 static const double 46 two54 = 0x1.0p54, /* 0x43500000, 0x00000000 */ 47 twom54 = 0x1.0p-54, /* 0x3C900000, 0x00000000 */ 48 huge = 1.0e+300, 49 tiny = 1.0e-300; 50 51 #ifdef _LP64 52 double 53 scalbn(double x, int n) 54 { 55 return scalbln(x, n); 56 } 57 #endif 58 59 double 60 scalbln(double x, long n) 61 { 62 int32_t k,hx,lx; 63 EXTRACT_WORDS(hx,lx,x); 64 k = ((uint32_t)hx&0x7ff00000)>>20; /* extract exponent */ 65 if (k==0) { /* 0 or subnormal x */ 66 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ 67 x *= two54; 68 GET_HIGH_WORD(hx,x); 69 k = (((uint32_t)hx&0x7ff00000)>>20) - 54; 70 if (n< -50000) return tiny*x; /*underflow*/ 71 } 72 if (k==0x7ff) return x+x; /* NaN or Inf */ 73 k = k+n; 74 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */ 75 if (k > 0) /* normal result */ 76 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} 77 if (k <= -54) { 78 if (n > 50000) /* in case integer overflow in n+k */ 79 return huge*copysign(huge,x); /*overflow*/ 80 else return tiny*copysign(tiny,x); /*underflow*/ 81 } 82 k += 54; /* subnormal result */ 83 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); 84 return x*twom54; 85 } 86