63 lines
1.4 KiB
C
63 lines
1.4 KiB
C
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/* _FDscale 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 _FDscale(float *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[_F0] & _FMASK) >> _FOFF;
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if (xchar == _FMAX)
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return ((ps[_F0] & _FFRAC) != 0 || ps[_F1] != 0
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? NAN : INF);
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else if (xchar == 0 && 0 < (xchar = _FDnorm(ps)))
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return (0);
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lexp += xchar;
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if (_FMAX <= lexp)
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{ /* overflow, return +/-INF */
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*px = ps[_F0] & _FSIGN ? -_FInf._F : _FInf._F;
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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[_F0] = ps[_F0] & ~_FMASK | (short)lexp << _FOFF;
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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[_F0] & _FSIGN;
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ps[_F0] = 1 << _FOFF | ps[_F0] & _FFRAC;
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if (--lexp < -(16+_FOFF))
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{ /* underflow, return +/-0 */
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ps[_F0] = sign, ps[_F1] = 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 = (short)lexp;
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if (xexp <= -16)
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ps[_F1] = ps[_F0], ps[_F0] = 0, xexp += 16;
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if ((xexp = -xexp) != 0)
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{ /* scale by bits */
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ps[_F1] = ps[_F1] >> xexp
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| ps[_F0] << (16 - xexp);
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ps[_F0] >>= xexp;
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}
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ps[_F0] |= 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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