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 #ifndef lint 14 static char rcsid[] = "$FreeBSD$"; 15 #endif 16 17 /* 18 * scalbnl (long double x, int n) 19 * scalbnl(x,n) returns x* 2**n computed by exponent 20 * manipulation rather than by actually performing an 21 * exponentiation or a multiplication. 22 */ 23 24 /* 25 * We assume that a long double has a 15-bit exponent. On systems 26 * where long double is the same as double, scalbnl() is an alias 27 * for scalbn(), so we don't use this routine. 28 */ 29 30 #include <sys/cdefs.h> 31 #include <float.h> 32 #include <math.h> 33 34 #include "fpmath.h" 35 36 #if LDBL_MAX_EXP != 0x4000 37 #error "Unsupported long double format" 38 #endif 39 40 static const long double 41 huge = 0x1p16000L, 42 tiny = 0x1p-16000L; 43 44 long double 45 scalbnl (long double x, int n) 46 { 47 union IEEEl2bits u; 48 int k; 49 u.e = x; 50 k = u.bits.exp; /* extract exponent */ 51 if (k==0) { /* 0 or subnormal x */ 52 if ((u.bits.manh|u.bits.manl)==0) return x; /* +-0 */ 53 u.e *= 0x1p+128; 54 k = u.bits.exp - 128; 55 if (n< -50000) return tiny*x; /*underflow*/ 56 } 57 if (k==0x7fff) return x+x; /* NaN or Inf */ 58 k = k+n; 59 if (k >= 0x7fff) return huge*copysignl(huge,x); /* overflow */ 60 if (k > 0) /* normal result */ 61 {u.bits.exp = k; return u.e;} 62 if (k <= -128) 63 if (n > 50000) /* in case integer overflow in n+k */ 64 return huge*copysign(huge,x); /*overflow*/ 65 else return tiny*copysign(tiny,x); /*underflow*/ 66 k += 128; /* subnormal result */ 67 u.bits.exp = k; 68 return u.e*0x1p-128; 69 } 70 71 __strong_reference(scalbnl, ldexpl); 72