71 lines
1.7 KiB
C
71 lines
1.7 KiB
C
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/* _Dscale function -- IEEE 754 version */
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#include "wctype.h"
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#include "xmath.h"
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_STD_BEGIN
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_CRTIMP2 short _Dscale(double *px, long lexp)
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{ /* scale *px by 2^xexp with checking */
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unsigned short *ps = (unsigned short *)px;
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short xchar = (ps[_D0] & _DMASK) >> _DOFF;
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if (xchar == _DMAX)
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return ((ps[_D0] & _DFRAC) != 0 || ps[_D1] != 0
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|| ps[_D2] != 0 || ps[_D3] != 0 ? NAN : INF);
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else if (xchar == 0 && 0 < (xchar = _Dnorm(ps)))
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return (0);
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lexp += xchar;
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if (_DMAX <= lexp)
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{ /* overflow, return +/-INF */
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*px = ps[_D0] & _DSIGN ? -_Inf._D : _Inf._D;
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return (INF);
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}
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else if (0 < lexp)
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{ /* finite result, repack */
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ps[_D0] = ps[_D0] & ~_DMASK | (short)lexp << _DOFF;
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return (FINITE);
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}
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else
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{ /* denormalized, scale */
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unsigned short sign = ps[_D0] & _DSIGN;
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ps[_D0] = 1 << _DOFF | ps[_D0] & _DFRAC;
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if (--lexp < -(48+_DOFF))
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{ /* underflow, return +/-0 */
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ps[_D0] = sign, ps[_D1] = 0;
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ps[_D2] = 0, ps[_D3] = 0;
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return (0);
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}
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else
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{ /* nonzero, align fraction */
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short xexp;
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for (xexp = (short)lexp; xexp <= -16; xexp += 16)
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{ /* scale by words */
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ps[_D3] = ps[_D2], ps[_D2] = ps[_D1];
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ps[_D1] = ps[_D0], ps[_D0] = 0;
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}
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if ((xexp = -xexp) != 0)
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{ /* scale by bits */
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ps[_D3] = ps[_D3] >> xexp
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| ps[_D2] << (16 - xexp);
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ps[_D2] = ps[_D2] >> xexp
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| ps[_D1] << (16 - xexp);
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ps[_D1] = ps[_D1] >> xexp
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| ps[_D0] << (16 - xexp);
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ps[_D0] >>= xexp;
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}
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ps[_D0] |= sign;
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return (FINITE);
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}
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}
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}
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_STD_END
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/*
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* Copyright (c) 1994 by P.J. Plauger. ALL RIGHTS RESERVED.
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* Consult your license regarding permissions and restrictions.
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*/
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/*
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941029 pjp: added _STD machinery
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*/
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