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/* mpfr_pow_si -- power function x^y with y an unsigned int
Copyright (C) 2001 Free Software Foundation, Inc.
This file is part of the MPFR Library.
The MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or (at your
option) any later version.
The MPFR Library 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 Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the MPFR Library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */
#include "gmp.h"
#include "gmp-impl.h"
#include "mpfr.h"
#include "mpfr-impl.h"
/* The computation of y=pow(x,z) is done by
y=pow_ui(x,z) if z>0
else
y=1/pow_ui(x,z) if z<0
*/
int
mpfr_pow_si (mpfr_ptr y, mpfr_srcptr x, long int n, mp_rnd_t rnd_mode)
{
if (n>0)
return mpfr_pow_ui(y,x,(unsigned long int)n,rnd_mode);
else
{
int inexact = 0;
n=-n;
/* x is NaN*/
if (MPFR_IS_NAN(x))
{
MPFR_SET_NAN(y);
return 1;
}
MPFR_CLEAR_NAN(y);
/* n=0 */
if(n==0)
return mpfr_set_ui(y,1,GMP_RNDN);;
/* case x is INF */
if(MPFR_IS_INF(x))
{
if(MPFR_SIGN(x)>0) /* +Inf */
{
MPFR_SET_ZERO(y);
if(MPFR_SIGN(y) < 0)
MPFR_CHANGE_SIGN(y);
return 0;
}
else
{
MPFR_SET_ZERO(y); /* -Inf */
if(!(n%2)) /* n is odd */
{
if(MPFR_SIGN(y) > 0)
MPFR_CHANGE_SIGN(y);
}
else /* n is not odd */
{
if(MPFR_SIGN(y) < 0)
MPFR_CHANGE_SIGN(y);
}
return 0;
}
}
/* case x=0 */
if(mpfr_cmp_ui(x,0) == 0)
{
if(!(n%2)) /* n is odd */
{
MPFR_SET_INF(y);
MPFR_SET_SAME_SIGN(y,x);
DIVIDE_BY_ZERO; /* Execption GMP*/
return 0;
}
else /* n is not odd */
{
MPFR_SET_INF(y);
if(MPFR_SIGN(y) < 0)
MPFR_CHANGE_SIGN(y);
DIVIDE_BY_ZERO; /* Execption GMP*/
return 0;
}
}
MPFR_CLEAR_INF(y);
/* General case */
{
/* Declaration of the intermediary variable */
mpfr_t t, ti;
/* Declaration of the size variable */
mp_prec_t Nx = MPFR_PREC(x); /* Precision of input variable */
mp_prec_t Ny = MPFR_PREC(y); /* Precision of input variable */
mp_prec_t Nt; /* Precision of the intermediary variable */
long int err; /* Precision of error */
/* compute the precision of intermediary variable */
Nt=MAX(Nx,Ny);
/* the optimal number of bits : see algorithms.ps */
Nt=Nt+3+_mpfr_ceil_log2(Nt);
/* initialise of intermediary variable */
mpfr_init(t);
mpfr_init(ti);
do {
/* reactualisation of the precision */
mpfr_set_prec(t,Nt);
mpfr_set_prec(ti,Nt);
/* compute 1/(x^n) n>0*/
mpfr_pow_ui(ti,y,(unsigned long int)(n),GMP_RNDN);
mpfr_ui_div(t,1,ti,GMP_RNDN);
/* estimation of the error -- see pow function in algorithms.ps*/
err = Nt - 3;
/* actualisation of the precision */
Nt += 10;
} while (err<0 || !mpfr_can_round(t,err,GMP_RNDN,rnd_mode,Ny));
inexact = mpfr_set(y,t,rnd_mode);
mpfr_clear(t);
mpfr_clear(ti);
}
return inexact;
}
}
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