M_LN2
assert(fabs(lgamma(3.0) - M_LN2) < DBL_EPSILON && signgam == 1);
assert(fabsf(lgammaf(3.0F) - (float)M_LN2) < FLT_EPSILON && signgam == 1);
M_LN2, M_PI, -2.0, 0.0,
d /= M_LN2;