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libmd/sqrt.c.src  view on Meta::CPAN

z = x;
#endif

/* Note, frexp and ldexp are used in order to
 * handle denormal numbers properly.
 */
#ifdef IBMPC
z = frexp( x, &e );
q = (short *)&x;
q += 3;
/*
e = ((*q >> 4) & 0x0fff) - 0x3fe;
*q &= 0x000f;
*q |= 0x3fe0;
z = x;
*/
#endif
#ifdef MIEEE
z = frexp( x, &e );
q = (short *)&x;
/*
e = ((*q >> 4) & 0x0fff) - 0x3fe;
*q &= 0x000f;
*q |= 0x3fe0;
z = x;
*/
#endif

/* approximate square root of number between 0.5 and 1
 * relative error of approximation = 7.47e-3
 */
x = 4.173075996388649989089E-1 + 5.9016206709064458299663E-1 * z;

/* adjust for odd powers of 2 */
if( (e & 1) != 0 )
	x *= SQRT2;

/* re-insert exponent */
#ifdef UNK
x = ldexp( x, (e >> 1) );
#endif
#ifdef DEC
*q += ((e >> 1) & 0377) << 7;
*q &= 077777;
#endif
#ifdef IBMPC
x = ldexp( x, (e >> 1) );
/*
*q += ((e >>1) & 0x7ff) << 4;
*q &= 077777;
*/
#endif
#ifdef MIEEE
x = ldexp( x, (e >> 1) );
/*
*q += ((e >>1) & 0x7ff) << 4;
*q &= 077777;
*/
#endif

/* Newton iterations: */
#ifdef UNK
x = 0.5*(x + w/x);
x = 0.5*(x + w/x);
x = 0.5*(x + w/x);
#endif

/* Note, assume the square root cannot be denormal,
 * so it is safe to use integer exponent operations here.
 */
#ifdef DEC
x += w/x;
*q -= 0200;
x += w/x;
*q -= 0200;
x += w/x;
*q -= 0200;
#endif
#ifdef IBMPC
x += w/x;
*q -= 0x10;
x += w/x;
*q -= 0x10;
x += w/x;
*q -= 0x10;
#endif
#ifdef MIEEE
x += w/x;
*q -= 0x10;
x += w/x;
*q -= 0x10;
x += w/x;
*q -= 0x10;
#endif

return(x);
}