1 files changed, 134 insertions, 0 deletions
diff --git a/mpfr/log1p.c b/mpfr/log1p.c
new file mode 100644
index 000000000..3eb4d110e
--- /dev/null
+++ b/mpfr/log1p.c
@@ -0,0 +1,134 @@
+/* mpfr_log1p -- Compute log(1+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 log1p is done by
+
+    log1p(x)=log(1+x)
+ */
+
+int
+mpfr_log1p (mpfr_ptr y, mpfr_srcptr x , mp_rnd_t rnd_mode) 
+{
+  int comp, inexact = 0;
+
+  if (MPFR_IS_NAN(x)) 
+    {
+      MPFR_SET_NAN(y); 
+      return 1; 
+    }
+  MPFR_CLEAR_NAN(y);
+
+  /* check for inf or -inf (result is not defined) */
+  if (MPFR_IS_INF(x))
+    { 
+      if(MPFR_SIGN(x) > 0)
+        {
+          MPFR_SET_INF(y);
+          
+          if (MPFR_SIGN(y) < 0) 
+            MPFR_CHANGE_SIGN(y);
+          
+          return 0;
+        }
+      else
+        {
+          MPFR_SET_NAN(y);
+          return 1;
+        }
+    }
+
+  comp = mpfr_cmp_si(x,-1);
+  /* x<-1 undefined */
+  if(comp < 0) 
+    {     
+      MPFR_SET_NAN(y); 
+      return 1;
+    }
+  /* x=0: log1p(-1)=-inf (division by zero) */
+  if(comp == 0)
+    {
+      DIVIDE_BY_ZERO; /* Exception GMP */
+      MPFR_SET_INF(y); 
+      if (MPFR_SIGN(y) > 0) 
+        MPFR_CHANGE_SIGN(y);
+      return 1;
+    }
+
+  MPFR_CLEAR_INF(y);
+
+  if(!MPFR_NOTZERO(x))
+    {
+      MPFR_SET_ZERO(y);   /* log1p(+/- 0) = +/- 0 */
+      MPFR_SET_SAME_SIGN(y, x);
+      return 0;
+    }
+
+
+  /* General case */
+  {
+    /* Declaration of the intermediary variable */
+    mpfr_t t;
+
+    /* 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);             
+
+    /* First computation of cosh */
+    do {
+
+      /* reactualisation of the precision */
+      mpfr_set_prec(t, Nt);
+      
+      /* compute log1p */
+      mpfr_add_ui (t, x, 1, GMP_RNDN);   /* 1+x */
+      mpfr_log (t, t, GMP_RNDN);        /* log(1+x)*/
+
+      /* estimation of the error */
+      /*err=Nt-(_mpfr_ceil_log2(1+pow(2,1-MPFR_EXP(t))));*/
+      err=Nt-(MAX(1-MPFR_EXP(t),0)+1);
+
+      /* 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);
+  }
+  return inexact;
+}