1cd7d05b5SDavid Schultz /* @(#)s_scalbn.c 5.1 93/09/24 */ 2cd7d05b5SDavid Schultz /* 3cd7d05b5SDavid Schultz * ==================================================== 4cd7d05b5SDavid Schultz * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5cd7d05b5SDavid Schultz * 6cd7d05b5SDavid Schultz * Developed at SunPro, a Sun Microsystems, Inc. business. 7cd7d05b5SDavid Schultz * Permission to use, copy, modify, and distribute this 8cd7d05b5SDavid Schultz * software is freely granted, provided that this notice 9cd7d05b5SDavid Schultz * is preserved. 10cd7d05b5SDavid Schultz * ==================================================== 11cd7d05b5SDavid Schultz */ 12cd7d05b5SDavid Schultz 13cd7d05b5SDavid Schultz #ifndef lint 14cd7d05b5SDavid Schultz static char rcsid[] = "$FreeBSD$"; 15cd7d05b5SDavid Schultz #endif 16cd7d05b5SDavid Schultz 17cd7d05b5SDavid Schultz /* 18cd7d05b5SDavid Schultz * scalbnl (long double x, int n) 19cd7d05b5SDavid Schultz * scalbnl(x,n) returns x* 2**n computed by exponent 20cd7d05b5SDavid Schultz * manipulation rather than by actually performing an 21cd7d05b5SDavid Schultz * exponentiation or a multiplication. 22cd7d05b5SDavid Schultz */ 23cd7d05b5SDavid Schultz 24cd7d05b5SDavid Schultz /* 25cd7d05b5SDavid Schultz * We assume that a long double has a 15-bit exponent. On systems 26cd7d05b5SDavid Schultz * where long double is the same as double, scalbnl() is an alias 27cd7d05b5SDavid Schultz * for scalbn(), so we don't use this routine. 28cd7d05b5SDavid Schultz */ 29cd7d05b5SDavid Schultz 30cd7d05b5SDavid Schultz #include <sys/cdefs.h> 31cd7d05b5SDavid Schultz #include <float.h> 32cd7d05b5SDavid Schultz #include <math.h> 33cd7d05b5SDavid Schultz 34cd7d05b5SDavid Schultz #include "fpmath.h" 35cd7d05b5SDavid Schultz 36cd7d05b5SDavid Schultz #if LDBL_MAX_EXP != 0x4000 37cd7d05b5SDavid Schultz #error "Unsupported long double format" 38cd7d05b5SDavid Schultz #endif 39cd7d05b5SDavid Schultz 40cd7d05b5SDavid Schultz static const long double 41cd7d05b5SDavid Schultz huge = 0x1p16000L, 42cd7d05b5SDavid Schultz tiny = 0x1p-16000L; 43cd7d05b5SDavid Schultz 44cd7d05b5SDavid Schultz long double 45cd7d05b5SDavid Schultz scalbnl (long double x, int n) 46cd7d05b5SDavid Schultz { 47cd7d05b5SDavid Schultz union IEEEl2bits u; 48cd7d05b5SDavid Schultz int k; 49cd7d05b5SDavid Schultz u.e = x; 50cd7d05b5SDavid Schultz k = u.bits.exp; /* extract exponent */ 51cd7d05b5SDavid Schultz if (k==0) { /* 0 or subnormal x */ 52cd7d05b5SDavid Schultz if ((u.bits.manh|u.bits.manl)==0) return x; /* +-0 */ 53cd7d05b5SDavid Schultz u.e *= 0x1p+128; 54cd7d05b5SDavid Schultz k = u.bits.exp - 128; 55cd7d05b5SDavid Schultz if (n< -50000) return tiny*x; /*underflow*/ 56cd7d05b5SDavid Schultz } 57cd7d05b5SDavid Schultz if (k==0x7fff) return x+x; /* NaN or Inf */ 58cd7d05b5SDavid Schultz k = k+n; 59cd7d05b5SDavid Schultz if (k >= 0x7fff) return huge*copysignl(huge,x); /* overflow */ 60cd7d05b5SDavid Schultz if (k > 0) /* normal result */ 61cd7d05b5SDavid Schultz {u.bits.exp = k; return u.e;} 62cd7d05b5SDavid Schultz if (k <= -128) 63cd7d05b5SDavid Schultz if (n > 50000) /* in case integer overflow in n+k */ 64cd7d05b5SDavid Schultz return huge*copysign(huge,x); /*overflow*/ 65cd7d05b5SDavid Schultz else return tiny*copysign(tiny,x); /*underflow*/ 66cd7d05b5SDavid Schultz k += 128; /* subnormal result */ 67cd7d05b5SDavid Schultz u.bits.exp = k; 68cd7d05b5SDavid Schultz return u.e*0x1p-128; 69cd7d05b5SDavid Schultz } 70cd7d05b5SDavid Schultz 71cd7d05b5SDavid Schultz __strong_reference(scalbnl, ldexpl); 72