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/* ldfloor() -- long double floor
** public domain by Raymond Gardner Englewood, CO
** tested with TC++
** assumptions: 80-bit IEEE format numbers, stored LSB first
** (Intel style), longs & ints are accessed from arbitrary boundaries
*/
long double ldfloor(long double a)
{
long double a0;
int e, n;
a0 = a;
e = ((int *)&a)[4] & 0x7FFF; /* extract exponent */
if ( e == 0 ) /* 0 is special case */
return (long double) 0.0;
e -= 16383; /* unbias exponent */
if (e < 0) /* if < 0, num is < 1,... */
{
a = 0.0; /* so floor is zero */
}
else if ((n = 63 - e) > 0) /* clear n least sig. bits */
{
if (n < 32) /* clear n lowest bits */
{
((unsigned long *)&a)[0] &= ~((1L << n) - 1);
}
else /* n >= 32 */
{
((unsigned long *)&a)[0] = 0; /* clear lower 32 bits */
n -= 32; /* how many left to clear ? */
if (n) /* if any, clear n next lowest bits */
{
((unsigned long *)&a)[1] &= ~((1L << n) - 1);
}
}
}
if (a0 < 0 && a0 != a) /* if neg. and it had fractional bits */
a -= 1.0; /* adjust the floor */
return a; /* return it */
}
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