diff options
Diffstat (limited to 'mpfr/ui_pow.c')
-rw-r--r-- | mpfr/ui_pow.c | 119 |
1 files changed, 119 insertions, 0 deletions
diff --git a/mpfr/ui_pow.c b/mpfr/ui_pow.c new file mode 100644 index 000000000..ac3cb52dd --- /dev/null +++ b/mpfr/ui_pow.c @@ -0,0 +1,119 @@ +/* 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; + +} |