Annotation of OpenXM_contrib/gmp/mpfr/log2.c, Revision 1.1.1.2
1.1.1.2 ! ohara 1: /* mpfr_log2 -- log base 2
1.1 maekawa 2:
1.1.1.2 ! ohara 3: Copyright 2001, 2002 Free Software Foundation, Inc.
1.1 maekawa 4:
5: This file is part of the MPFR Library.
6:
7: The MPFR Library is free software; you can redistribute it and/or modify
1.1.1.2 ! ohara 8: it under the terms of the GNU Lesser General Public License as published by
! 9: the Free Software Foundation; either version 2.1 of the License, or (at your
1.1 maekawa 10: option) any later version.
11:
12: The MPFR Library is distributed in the hope that it will be useful, but
13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
1.1.1.2 ! ohara 14: or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
1.1 maekawa 15: License for more details.
16:
1.1.1.2 ! ohara 17: You should have received a copy of the GNU Lesser General Public License
1.1 maekawa 18: along with the MPFR Library; see the file COPYING.LIB. If not, write to
19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
20: MA 02111-1307, USA. */
21:
22: #include <stdio.h>
23: #include "gmp.h"
24: #include "gmp-impl.h"
25: #include "mpfr.h"
1.1.1.2 ! ohara 26: #include "mpfr-impl.h"
1.1 maekawa 27:
1.1.1.2 ! ohara 28: /* The computation of r=log2(a)
1.1 maekawa 29:
1.1.1.2 ! ohara 30: r=log2(a)=log(a)/log(2)
! 31: */
1.1 maekawa 32:
1.1.1.2 ! ohara 33: int
! 34: mpfr_log2 (mpfr_ptr r, mpfr_srcptr a, mp_rnd_t rnd_mode)
1.1 maekawa 35: {
1.1.1.2 ! ohara 36: int inexact = 0;
1.1 maekawa 37:
1.1.1.2 ! ohara 38: /* If a is NaN, the result is NaN */
! 39: if (MPFR_IS_NAN(a))
! 40: {
! 41: MPFR_SET_NAN(r);
! 42: MPFR_RET_NAN;
! 43: }
! 44:
! 45: MPFR_CLEAR_NAN(r);
! 46:
! 47: /* check for infinity before zero */
! 48: if (MPFR_IS_INF(a))
! 49: {
! 50: if (MPFR_SIGN(a) < 0) /* log(-Inf) = NaN */
! 51: {
! 52: MPFR_SET_NAN(r);
! 53: MPFR_RET_NAN;
! 54: }
! 55: else /* log(+Inf) = +Inf */
! 56: {
! 57: MPFR_SET_INF(r);
! 58: MPFR_SET_POS(r);
! 59: MPFR_RET(0);
! 60: }
! 61: }
! 62:
! 63: /* Now we can clear the flags without damage even if r == a */
! 64: MPFR_CLEAR_INF(r);
! 65:
! 66: if (MPFR_IS_ZERO(a))
! 67: {
! 68: MPFR_SET_INF(r);
! 69: MPFR_SET_NEG(r);
! 70: MPFR_RET(0); /* log2(0) is an exact -infinity */
! 71: }
! 72:
! 73: /* If a is negative, the result is NaN */
! 74: if (MPFR_SIGN(a) < 0)
! 75: {
! 76: MPFR_SET_NAN(r);
! 77: MPFR_RET_NAN;
! 78: }
! 79:
! 80: /* If a is 1, the result is 0 */
! 81: if (mpfr_cmp_ui(a, 1) == 0)
! 82: {
! 83: MPFR_SET_ZERO(r);
! 84: MPFR_SET_POS(r);
! 85: MPFR_RET(0); /* only "normal" case where the result is exact */
! 86: }
! 87:
! 88: /* If a is integer, log2(a) is exact*/
! 89: if (mpfr_cmp_ui_2exp(a,1,MPFR_EXP(a)-1) == 0)
! 90: return mpfr_set_si(r,MPFR_EXP(a)-1,rnd_mode);
! 91:
! 92:
! 93: /* General case */
! 94: {
! 95: /* Declaration of the intermediary variable */
! 96: mpfr_t t, tt;
! 97:
! 98: /* Declaration of the size variable */
! 99: mp_prec_t Nx = MPFR_PREC(a); /* Precision of input variable */
! 100: mp_prec_t Ny = MPFR_PREC(r); /* Precision of input variable */
! 101:
! 102: mp_prec_t Nt; /* Precision of the intermediary variable */
! 103: long int err; /* Precision of error */
! 104:
! 105:
! 106: /* compute the precision of intermediary variable */
! 107: Nt=MAX(Nx,Ny);
! 108: /* the optimal number of bits : see algorithms.ps */
! 109: Nt=Nt+3+_mpfr_ceil_log2(Nt);
! 110:
! 111: /* initialise of intermediary variable */
! 112: mpfr_init(t);
! 113: mpfr_init(tt);
! 114:
! 115:
! 116: /* First computation of log2 */
! 117: do {
! 118:
! 119: /* reactualisation of the precision */
! 120: mpfr_set_prec(t,Nt);
! 121: mpfr_set_prec(tt,Nt);
! 122:
! 123: /* compute log2 */
! 124: mpfr_const_log2(t,GMP_RNDD); /* log(2) */
! 125: mpfr_log(tt,a,GMP_RNDN); /* log(a) */
! 126: mpfr_div(t,tt,t,GMP_RNDN); /* log(a)/log(2) */
! 127:
! 128:
! 129: /* estimation of the error */
! 130: err=Nt-3;
! 131:
! 132: /* actualisation of the precision */
! 133: Nt += 10;
! 134: } while ((err<0) || !mpfr_can_round(t,err,GMP_RNDN,rnd_mode,Ny));
! 135:
! 136: inexact = mpfr_set(r,t,rnd_mode);
1.1 maekawa 137:
1.1.1.2 ! ohara 138: mpfr_clear(t);
! 139: mpfr_clear(tt);
1.1 maekawa 140: }
1.1.1.2 ! ohara 141: return inexact;
1.1 maekawa 142: }
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