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/* $OpenBSD: s_scalbnl.c,v 1.4 2016/09/12 19:47:02 guenther Exp $ */ |
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/* @(#)s_scalbn.c 5.1 93/09/24 */ |
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/* |
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* ==================================================== |
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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* |
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* Developed at SunPro, a Sun Microsystems, Inc. business. |
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* Permission to use, copy, modify, and distribute this |
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* software is freely granted, provided that this notice |
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* is preserved. |
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* ==================================================== |
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*/ |
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/* |
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* scalbnl (long double x, int n) |
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* scalbnl(x,n) returns x* 2**n computed by exponent |
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* manipulation rather than by actually performing an |
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* exponentiation or a multiplication. |
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*/ |
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/* |
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* We assume that a long double has a 15-bit exponent. On systems |
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* where long double is the same as double, scalbnl() is an alias |
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* for scalbn(), so we don't use this routine. |
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*/ |
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#include <sys/types.h> |
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#include <machine/ieee.h> |
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#include <float.h> |
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#include <math.h> |
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#if LDBL_MAX_EXP != 0x4000 |
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#error "Unsupported long double format" |
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#endif |
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static const long double |
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huge = 0x1p16000L, |
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tiny = 0x1p-16000L; |
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long double |
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scalbnl (long double x, int n) |
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{ |
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union { |
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long double e; |
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struct ieee_ext bits; |
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} u; |
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int k; |
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u.e = x; |
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k = u.bits.ext_exp; /* extract exponent */ |
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✓✓ |
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if (k==0) { /* 0 or subnormal x */ |
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✓✗ |
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if ((u.bits.ext_frach |
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#ifdef EXT_FRACHMBITS |
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| u.bits.ext_frachm |
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#endif /* EXT_FRACHMBITS */ |
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#ifdef EXT_FRACLMBITS |
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| u.bits.ext_fraclm |
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#endif /* EXT_FRACLMBITS */ |
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| u.bits.ext_fracl)==0) return x; /* +-0 */ |
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u.e *= 0x1p+128; |
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k = u.bits.ext_exp - 128; |
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if (n< -50000) return tiny*x; /*underflow*/ |
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} |
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✗✓ |
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if (k==0x7fff) return x+x; /* NaN or Inf */ |
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k = k+n; |
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✗✓ |
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if (k >= 0x7fff) return huge*copysignl(huge,x); /* overflow */ |
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✓✗ |
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if (k > 0) /* normal result */ |
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{u.bits.ext_exp = k; return u.e;} |
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if (k <= -128) { |
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if (n > 50000) /* in case integer overflow in n+k */ |
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return huge*copysign(huge,x); /*overflow*/ |
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else return tiny*copysign(tiny,x); /*underflow*/ |
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} |
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k += 128; /* subnormal result */ |
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u.bits.ext_exp = k; |
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return u.e*0x1p-128; |
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} |
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DEF_STD(scalbnl); |
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long double |
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ldexpl(long double x, int n) |
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{ |
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return scalbnl(x, n); |
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} |
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DEF_STD(ldexpl); |