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