===================================================================
RCS file: /home/cvs/OpenXM_contrib/gmp/mpfr/Attic/log2.c,v
retrieving revision 1.1
retrieving revision 1.1.1.2
diff -u -p -r1.1 -r1.1.1.2
--- OpenXM_contrib/gmp/mpfr/Attic/log2.c	2000/09/09 14:12:19	1.1
+++ OpenXM_contrib/gmp/mpfr/Attic/log2.c	2003/08/25 16:06:08	1.1.1.2
@@ -1,102 +1,142 @@
-/* mpfr_log2 -- compute natural logarithm of 2
+/* mpfr_log2 -- log base 2
 
-Copyright (C) 1999 PolKA project, Inria Lorraine and Loria
+Copyright 2001, 2002 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 Library General Public License as published by
-the Free Software Foundation; either version 2 of the License, or (at your
+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 Library General Public
+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 Library General Public License
+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 <stdio.h>
-#include <math.h>
 #include "gmp.h"
 #include "gmp-impl.h"
-#include "longlong.h"
 #include "mpfr.h"
+#include "mpfr-impl.h"
 
-mpfr_t __mpfr_log2; /* stored value of log(2) with rnd_mode=GMP_RNDZ */
-int __mpfr_log2_prec=0; /* precision of stored value */
+ /* The computation of r=log2(a)
 
-/* set x to log(2) rounded to precision PREC(x) with direction rnd_mode 
+    r=log2(a)=log(a)/log(2)
+ */
 
-   use formula log(2) = sum(1/k/2^k, k=1..infinity)
+int
+mpfr_log2 (mpfr_ptr r, mpfr_srcptr a, mp_rnd_t rnd_mode)
+{
+  int inexact = 0;
 
-   whence 2^N*log(2) = S(N) + R(N)
+  /* If a is NaN, the result is NaN */
+  if (MPFR_IS_NAN(a))
+    {  
+      MPFR_SET_NAN(r);
+      MPFR_RET_NAN;
+    }
 
-   where S(N) = sum(2^(N-k)/k, k=1..N-1)
-   and   R(N) = sum(1/k/2^(k-N), k=N..infinity) < 2/N
+  MPFR_CLEAR_NAN(r);
 
-   Let S'(N) = sum(floor(2^(N-k)/k), k=1..N-1)
+  /* check for infinity before zero */
+  if (MPFR_IS_INF(a))
+    {
+      if (MPFR_SIGN(a) < 0) /* log(-Inf) = NaN */
+        {
+          MPFR_SET_NAN(r);
+          MPFR_RET_NAN;
+        }
+      else /* log(+Inf) = +Inf */
+        {
+          MPFR_SET_INF(r);
+          MPFR_SET_POS(r);
+          MPFR_RET(0);
+        }
+    }
 
-   Then 2^N*log(2)-S'(N) <= N-1+2/N <= N for N>=2.
-*/
-void 
-#if __STDC__
-mpfr_log2(mpfr_ptr x, unsigned char rnd_mode)
-#else
-mpfr_log2(x, rnd_mode) mpfr_ptr x; unsigned char rnd_mode;
-#endif
-{
-  int N, oldN, k, precx; mpz_t s, t, u;
+  /* Now we can clear the flags without damage even if r == a */
+  MPFR_CLEAR_INF(r);
 
-  precx = PREC(x);
+  if (MPFR_IS_ZERO(a))
+    {
+      MPFR_SET_INF(r);
+      MPFR_SET_NEG(r);
+      MPFR_RET(0); /* log2(0) is an exact -infinity */
+    }
 
-  /* has stored value enough precision ? */
-  if (precx <= __mpfr_log2_prec) {
-    if (rnd_mode==GMP_RNDZ || rnd_mode==GMP_RNDD ||
-	mpfr_can_round(__mpfr_log2, __mpfr_log2_prec, GMP_RNDZ, rnd_mode, precx))
-      {
-	mpfr_set(x, __mpfr_log2, rnd_mode); return; 
-      }
-  }
+  /* If a is negative, the result is NaN */
+  if (MPFR_SIGN(a) < 0)
+    {
+      MPFR_SET_NAN(r);
+      MPFR_RET_NAN;
+    }
 
-  /* need to recompute */
-  N=2;
-  do {
-    oldN = N;
-    N = precx + (int)ceil(log((double)N)/log(2.0));
-  } while (N != oldN);
-  mpz_init_set_ui(s,0);
-  mpz_init(u);
-  mpz_init_set_ui(t,1); 
-#if 0
-  /* use log(2) = sum(1/k/2^k, k=1..infinity) */
-  mpz_mul_2exp(t, t, N);
-  for (k=1;k<N;k++) {
-    mpz_div_2exp(t, t, 1);
-    mpz_fdiv_q_ui(u, t, k);
-    mpz_add(s, s, u);
-  }
-#else
-  /* use log(2) = sum((6*k-1)/(2*k^2-k)/2^(2*k+1), k=1..infinity) */
-  mpz_mul_2exp(t, t, N-1);
-  for (k=1;k<N/2;k++) {
-    mpz_div_2exp(t, t, 2);
-    mpz_mul_ui(u, t, 6*k-1);
-    mpz_fdiv_q_ui(u, u, k*(2*k-1));
-    mpz_add(s, s, u);
-  }
-#endif
-  mpfr_set_z(x, s, rnd_mode);
-  EXP(x) -= N;
+  /* If a is 1, the result is 0 */
+  if (mpfr_cmp_ui(a, 1) == 0)
+    {
+      MPFR_SET_ZERO(r);
+      MPFR_SET_POS(r);
+      MPFR_RET(0); /* only "normal" case where the result is exact */
+    }
 
-  /* stored computed value */
-  if (__mpfr_log2_prec==0) mpfr_init2(__mpfr_log2, precx);
-  else mpfr_set_prec(__mpfr_log2, precx);
-  mpfr_set(__mpfr_log2, x, GMP_RNDZ);
-  __mpfr_log2_prec=precx;
+  /* If a is integer, log2(a) is exact*/
+  if (mpfr_cmp_ui_2exp(a,1,MPFR_EXP(a)-1) == 0)
+      return mpfr_set_si(r,MPFR_EXP(a)-1,rnd_mode); 
 
-  mpz_clear(s); mpz_clear(t); mpz_clear(u);
+
+ /* General case */
+  {
+    /* Declaration of the intermediary variable */
+    mpfr_t t, tt;
+
+    /* Declaration of the size variable */
+    mp_prec_t Nx = MPFR_PREC(a);   /* Precision of input variable */
+    mp_prec_t Ny = MPFR_PREC(r);   /* 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(tt);             
+
+    
+    /* First computation of log2 */
+    do {
+
+      /* reactualisation of the precision */
+      mpfr_set_prec(t,Nt);             
+      mpfr_set_prec(tt,Nt);             
+      
+      /* compute log2 */
+      mpfr_const_log2(t,GMP_RNDD); /* log(2) */
+      mpfr_log(tt,a,GMP_RNDN);     /* log(a) */
+      mpfr_div(t,tt,t,GMP_RNDN); /* log(a)/log(2) */
+
+
+      /* estimation of the error */
+      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(r,t,rnd_mode);
+
+      mpfr_clear(t);
+      mpfr_clear(tt);
+  }
+  return inexact;
 }