1 /* $OpenBSD: s_scalbnl.c,v 1.3 2013/11/12 18:28:02 martynas Exp $ */ 2 /* @(#)s_scalbn.c 5.1 93/09/24 */ 3 /* 4 * ==================================================== 5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 6 * 7 * Developed at SunPro, 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 * scalbnl (long double x, int n) 16 * scalbnl(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 /* 22 * We assume that a long double has a 15-bit exponent. On systems 23 * where long double is the same as double, scalbnl() is an alias 24 * for scalbn(), so we don't use this routine. 25 */ 26 27 #include <sys/types.h> 28 #include <machine/ieee.h> 29 #include <float.h> 30 #include <math.h> 31 32 #if LDBL_MAX_EXP != 0x4000 33 #error "Unsupported long double format" 34 #endif 35 36 static const long double 37 huge = 0x1p16000L, 38 tiny = 0x1p-16000L; 39 40 long double 41 scalbnl (long double x, int n) 42 { 43 union { 44 long double e; 45 struct ieee_ext bits; 46 } u; 47 int k; 48 u.e = x; 49 k = u.bits.ext_exp; /* extract exponent */ 50 if (k==0) { /* 0 or subnormal x */ 51 if ((u.bits.ext_frach 52 #ifdef EXT_FRACHMBITS 53 | u.bits.ext_frachm 54 #endif /* EXT_FRACHMBITS */ 55 #ifdef EXT_FRACLMBITS 56 | u.bits.ext_fraclm 57 #endif /* EXT_FRACLMBITS */ 58 | u.bits.ext_fracl)==0) return x; /* +-0 */ 59 u.e *= 0x1p+128; 60 k = u.bits.ext_exp - 128; 61 if (n< -50000) return tiny*x; /*underflow*/ 62 } 63 if (k==0x7fff) return x+x; /* NaN or Inf */ 64 k = k+n; 65 if (k >= 0x7fff) return huge*copysignl(huge,x); /* overflow */ 66 if (k > 0) /* normal result */ 67 {u.bits.ext_exp = k; return u.e;} 68 if (k <= -128) { 69 if (n > 50000) /* in case integer overflow in n+k */ 70 return huge*copysign(huge,x); /*overflow*/ 71 else return tiny*copysign(tiny,x); /*underflow*/ 72 } 73 k += 128; /* subnormal result */ 74 u.bits.ext_exp = k; 75 return u.e*0x1p-128; 76 } 77 78 long double 79 ldexpl(long double x, int n) 80 { 81 return scalbnl(x, n); 82 } 83