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-rw-r--r--mpfr/ui_pow.c119
1 files changed, 119 insertions, 0 deletions
diff --git a/mpfr/ui_pow.c b/mpfr/ui_pow.c
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+/* mpfr_ui_pow -- power of n function n^x
+
+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(n,z) is done by
+
+ y=exp(z*log(n))=n^z
+ */
+
+int
+mpfr_ui_pow (mpfr_ptr y, unsigned long int n,mpfr_srcptr x, mp_rnd_t rnd_mode)
+{
+ int inexact;
+
+ if (MPFR_IS_NAN(x))
+ {
+ MPFR_SET_NAN(y);
+ return 1;
+ }
+
+ MPFR_CLEAR_NAN(y);
+
+ if (MPFR_IS_INF(x))
+ {
+ if (MPFR_SIGN(x) < 0)
+ {
+ MPFR_SET_ZERO(y);
+ if (MPFR_SIGN(y) < 0)
+ MPFR_CHANGE_SIGN(y);
+ return 0;
+ }
+ else
+ {
+ MPFR_SET_INF(y);
+ if(MPFR_SIGN(y) < 0)
+ MPFR_CHANGE_SIGN(y);
+ return 0;
+ }
+ }
+
+ /* n^0 = 1 */
+ if(mpfr_cmp_ui(x,0)==0)
+ {
+ return mpfr_set_ui(y,1,rnd_mode);
+ }
+
+ /* General case */
+ {
+ /* Declaration of the intermediary variable */
+ mpfr_t t, te, 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+5+_mpfr_ceil_log2(Nt);
+
+ /* initialise of intermediary variable */
+ mpfr_init(t);
+ mpfr_init2(ti,sizeof(unsigned long int)*8); /* 8 = CHAR_BIT */
+ mpfr_init(te);
+
+ do {
+
+ /* reactualisation of the precision */
+ mpfr_set_prec(t,Nt);
+ mpfr_set_prec(te,Nt);
+
+ /* compute exp(x*ln(n))*/
+ mpfr_set_ui(ti,n,GMP_RNDN); /* ti <- n*/
+ mpfr_log(t,ti,GMP_RNDU); /* ln(n) */
+ mpfr_mul(te,x,t,GMP_RNDU); /* x*ln(n) */
+ mpfr_exp(t,te,GMP_RNDN); /* exp(x*ln(n))*/
+
+ /* estimation of the error -- see pow function in algorithms.ps*/
+ err = Nt - (MPFR_EXP(te)+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);
+ mpfr_clear(te);
+ }
+ return inexact;
+
+}