char
_lngamma(
floatnum x,
int digits)
{
floatstruct factor;
int infinity;
char result;
if (float_cmp(x, &c1) == 0 || float_cmp(x, &c2) == 0)
return _setzero(x);
float_create(&factor);
result = _lngamma_prim(x, &factor, &infinity, digits)
&& infinity == 0;
if (result)
{
float_abs(&factor);
_ln(&factor, digits + 1);
result = float_sub(x, x, &factor, digits+1);
}
float_free(&factor);
if (infinity != 0)
return _seterror(x, ZeroDivide);
if (!result)
float_setnan(x);
return result;
}
/* evaluates ln(Gamma(x)) for all those x big
enough to let the asymptotic series converge directly.
Returns 0, if the result overflows
relative error for a 100 gigit calculation < 5e-100 */
static char
_lngammabigx(
floatnum x,
int digits)
{
floatstruct tmp1, tmp2;
char result;
result = 0;
float_create(&tmp1);
float_create(&tmp2);
/* compute (ln x-1) * (x-0.5) - 0.5 + ln(sqrt(2*pi)) */
float_copy(&tmp2, x, digits+1);
_ln(&tmp2, digits+1);
float_sub(&tmp2, &tmp2, &c1, digits+2);
float_sub(&tmp1, x, &c1Div2, digits+2);
if (float_mul(&tmp1, &tmp1, &tmp2, digits+2))
{
/* no overflow */
lngammaasymptotic(x, digits);
float_add(x, &tmp1, x, digits+3);
float_add(x, x, &cLnSqrt2PiMinusHalf, digits+3);
result = 1;
}
float_free(&tmp2);
float_free(&tmp1);
return result;
}
char
float_ln(floatnum x, int digits)
{
if (!chckmathparam(x, digits))
return 0;
if (float_getsign(x) <= 0)
return _seterror(x, OutOfDomain);
_ln(x, digits);
return 1;
}
char
float_lg(
floatnum x,
int digits)
{
floatstruct tmp;
int expx;
if (!chckmathparam(x, digits))
return 0;
if (float_getsign(x) <= 0)
return _seterror(x, OutOfDomain);
float_create(&tmp);
expx = float_getexponent(x);
float_setexponent(x, 0);
_ln(x, digits);
float_div(x, x, &cLn10, digits);
float_setinteger(&tmp, expx);
float_add(x, x, &tmp, digits);
float_free(&tmp);
return 1;
}
REAL _pow2(REAL a, REAL b, QByteArray &error)
{
return _ln(a, b, error) * _pow(a, b, error);
}
