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use table for const_euler at low prec

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This commit is contained in:
fredrik 2021-09-19 12:56:03 +02:00
parent 43a337041a
commit 9916182253
1 changed files with 28 additions and 1 deletions
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29
arb/const_euler.c
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@ -11,6 +11,7 @@
#include "arb.h"
#include "hypgeom.h"
#include "arb_hypgeom.h"
typedef struct
{
@ -333,5 +334,31 @@ arb_const_euler_eval(arb_t res, slong prec)
euler_bsplit_clear(sum);
}
ARB_DEF_CACHED_CONSTANT(arb_const_euler, arb_const_euler_eval)
ARB_DEF_CACHED_CONSTANT(arb_const_euler_brent_mcmillan, arb_const_euler_eval)
extern const mp_limb_t arb_hypgeom_gamma_tab_limbs[];
void
arb_const_euler(arb_t res, slong prec)
{
if (prec < ARB_HYPGEOM_GAMMA_TAB_PREC - 16)
{
slong exp;
mp_size_t n;
n = ARB_HYPGEOM_GAMMA_TAB_PREC / FLINT_BITS;
/* just reading the table is known to give the correct rounding */
_arf_set_round_mpn(arb_midref(res), &exp, arb_hypgeom_gamma_tab_limbs + n, n, 0, prec, ARF_RND_NEAR);
_fmpz_set_si_small(ARF_EXPREF(arb_midref(res)), exp);
/* 1/2 ulp error */
_fmpz_set_si_small(MAG_EXPREF(arb_radref(res)), exp - prec);
MAG_MAN(arb_radref(res)) = MAG_ONE_HALF;
}
else
{
arb_const_euler_brent_mcmillan(res, prec);
}
}