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66 lines
2.1 KiB
C
66 lines
2.1 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 (__glibc_unlikely (k == 0)) /* 0 or subnormal x */
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{
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if ((lx | (hx & 0x7fffffff)) == 0)
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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 (__glibc_unlikely (k == 0x7ff))
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return x + x; /* NaN or Inf */
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if (__glibc_unlikely (n < -50000))
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return tiny * __copysign (tiny, x); /*underflow*/
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if (__glibc_unlikely (n > 50000 || k + n > 0x7fe))
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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 (__glibc_likely (k > 0)) /* normal result */
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{
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SET_HIGH_WORD (x, (hx & 0x800fffff) | (k << 20)); return x;
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}
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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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