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optimize arb_digamma for small integers

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This commit is contained in:
Fredrik Johansson 2015-01-20 16:55:15 +01:00
parent 9f46fd1133
commit 43b98b6045
1 changed files with 38 additions and 0 deletions
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38
arb/digamma.c
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@ -24,6 +24,7 @@
******************************************************************************/
#include "arb.h"
#include "arith.h"
void arb_gamma_stirling_choose_param(int * reflect, long * r, long * n,
const arb_t x, int use_reflect, int digamma, long prec);
@ -37,6 +38,43 @@ arb_digamma(arb_t y, const arb_t x, long prec)
long r, n, wp;
arb_t t, u, v;
if (arb_is_exact(x))
{
const arf_struct * mid = arb_midref(x);
if (arf_is_special(mid))
{
arb_indeterminate(y);
return;
}
else if (arf_is_int(mid))
{
if (arf_sgn(mid) < 0)
{
arb_indeterminate(y);
return;
}
else if (arf_cmpabs_ui(mid, 30 + prec / 2) < 0)
{
fmpq_t h;
arb_init(t);
fmpq_init(h);
/* should change to fmpq_harmonic_ui when flint upgrades */
arith_harmonic_number(h, arf_get_si(mid, ARF_RND_DOWN) - 1);
arb_set_fmpq(y, h, prec + 2);
arb_const_euler(t, prec + 2);
arb_sub(y, y, t, prec);
arb_clear(t);
fmpq_clear(h);
return;
}
}
}
wp = prec + FLINT_BIT_COUNT(prec);
arb_gamma_stirling_choose_param(&reflect, &r, &n, x, 1, 1, wp);