mirror of
https://github.com/vale981/arb
synced 2025-03-05 09:21:38 -05:00
96 lines
2.7 KiB
C
96 lines
2.7 KiB
C
/*=============================================================================
|
|
|
|
This file is part of ARB.
|
|
|
|
ARB is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation; either version 2 of the License, or
|
|
(at your option) any later version.
|
|
|
|
ARB is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
GNU General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with ARB; if not, write to the Free Software
|
|
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
|
|
|
|
=============================================================================*/
|
|
/******************************************************************************
|
|
|
|
Copyright (C) 2014 Fredrik Johansson
|
|
|
|
******************************************************************************/
|
|
|
|
#include "mag.h"
|
|
#include "double_extras.h"
|
|
|
|
void
|
|
mag_log1p(mag_t z, const mag_t x)
|
|
{
|
|
if (mag_is_special(x))
|
|
{
|
|
if (mag_is_zero(x))
|
|
mag_zero(z);
|
|
else
|
|
mag_inf(z);
|
|
}
|
|
else
|
|
{
|
|
fmpz exp = MAG_EXP(x);
|
|
|
|
if (!COEFF_IS_MPZ(exp))
|
|
{
|
|
/* Quick bound by x */
|
|
if (exp < -10)
|
|
{
|
|
mag_set(z, x);
|
|
return;
|
|
}
|
|
else if (exp < 1000)
|
|
{
|
|
double t;
|
|
t = ldexp(MAG_MAN(x), exp - MAG_BITS);
|
|
t = (1.0 + t) * (1 + 1e-14);
|
|
t = mag_d_log_upper_bound(t);
|
|
mag_set_d(z, t);
|
|
return;
|
|
}
|
|
}
|
|
else if (fmpz_sgn(MAG_EXPREF(x)) < 0)
|
|
{
|
|
/* Quick bound by x */
|
|
mag_set(z, x);
|
|
return;
|
|
}
|
|
|
|
/* Now we must have x >= 2^1000 */
|
|
/* Use log(2^(exp-1) * (2*v)) = exp*log(2) + log(2*v) */
|
|
{
|
|
double t;
|
|
fmpz_t b;
|
|
mag_t u;
|
|
|
|
mag_init(u);
|
|
fmpz_init(b);
|
|
|
|
/* incrementing the mantissa gives an upper bound for x+1 */
|
|
t = ldexp(MAG_MAN(x) + 1, 1 - MAG_BITS);
|
|
t = mag_d_log_upper_bound(t);
|
|
mag_set_d(u, t);
|
|
|
|
/* log(2) < 744261118/2^30 */
|
|
_fmpz_add_fast(b, MAG_EXPREF(x), -1);
|
|
fmpz_mul_ui(b, b, 744261118);
|
|
mag_set_fmpz(z, b);
|
|
_fmpz_add_fast(MAG_EXPREF(z), MAG_EXPREF(z), -30);
|
|
|
|
mag_add(z, z, u);
|
|
|
|
mag_clear(u);
|
|
fmpz_clear(b);
|
|
}
|
|
}
|
|
}
|
|
|