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61 lines
1.8 KiB
C
61 lines
1.8 KiB
C
/*
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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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* scalbn (double x, int n)
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* scalbn(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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#include <math.h>
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#include <math_private.h>
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static const double
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two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
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twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
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huge = 1.0e+300,
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tiny = 1.0e-300;
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double
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__scalbn (double x, int n)
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{
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int32_t k,hx,lx;
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EXTRACT_WORDS(hx,lx,x);
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k = (hx&0x7ff00000)>>20; /* extract exponent */
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if (__builtin_expect(k==0, 0)) { /* 0 or subnormal x */
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if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
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x *= two54;
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GET_HIGH_WORD(hx,x);
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k = ((hx&0x7ff00000)>>20) - 54;
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}
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if (__builtin_expect(k==0x7ff, 0)) return x+x; /* NaN or Inf */
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if (__builtin_expect(n< -50000, 0))
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return tiny*__copysign(tiny,x); /*underflow*/
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if (__builtin_expect(n> 50000 || k+n > 0x7fe, 0))
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return huge*__copysign(huge,x); /* overflow */
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/* Now k and n are bounded we know that k = k+n does not
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overflow. */
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k = k+n;
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if (__builtin_expect(k > 0, 1)) /* normal result */
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{SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
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if (k <= -54)
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return tiny*__copysign(tiny,x); /*underflow*/
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k += 54; /* subnormal result */
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SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
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return x*twom54;
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}
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weak_alias (__scalbn, scalbn)
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#ifdef NO_LONG_DOUBLE
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strong_alias (__scalbn, __scalbnl)
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weak_alias (__scalbn, scalbnl)
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#endif
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