add the function expm1

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@1278 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 124 insertions, 0 deletions

diff --git a/expm1.c b/expm1.c
new file mode 100644
index 000000000..e357eb574
--- /dev/null
+++ b/expm1.c
@@ -0,0 +1,124 @@
+/* mpfr_expm1 -- Compute exp(x)-1
+
+Copyright (C) 2001 Free Software Foundation.
+
+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
+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
+License for more details.
+
+You should have received a copy of the GNU Library 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 "mpfr.h"
+#include "mpfr-impl.h"
+
+ /* The computation of expm1 is done by
+
+    expm1(x)=exp(x)-1
+ */
+int mpfr_expm1 _PROTO((mpfr_ptr, mpfr_srcptr, mp_rnd_t));
+
+int
+#if __STDC__
+mpfr_expm1 (mpfr_ptr y, mpfr_srcptr x , mp_rnd_t rnd_mode) 
+#else
+mpfr_expm1 (y, x, rnd_mode)
+     mpfr_ptr y;
+     mpfr_srcptr x;
+     mp_rnd_t rnd_mode;
+#endif
+{
+    
+  int inexact = 0;
+
+  if (MPFR_IS_NAN(x)) 
+    {
+      MPFR_SET_NAN(y); 
+      return 1; 
+    }
+  MPFR_CLEAR_NAN(y);
+
+
+  /* Test de l'entree = inf ou -inf (expm1(-inf)=-1)*/
+  if (MPFR_IS_INF(x))
+    { 
+      if(MPFR_SIGN(x) > 0)
+        {
+          MPFR_SET_INF(y);
+	  MPFR_SET_SAME_SIGN(y,x);    
+          return 0;
+        }
+      else  
+        return mpfr_set_ui(y,-1,rnd_mode);  
+    }
+
+  MPFR_CLEAR_INF(y);
+
+
+  if(!MPFR_NOTZERO(x))
+    {
+      MPFR_SET_ZERO(y);   /* expm1(+/- 0) = +/- 0 */
+      MPFR_SET_SAME_SIGN(y,x);
+      return 0;
+    }
+
+  /* General case */
+  {
+    /* Declaration of the intermediary variable */
+    mpfr_t te,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 */
+    mp_prec_t 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_init(te);             
+
+    /* First computation of cosh */
+    do {
+
+      /* reactualisation of the precision */
+      mpfr_set_prec(t,Nt);
+      mpfr_set_prec(te,Nt);
+      
+      /* compute expm1 */
+      mpfr_exp(te,x,GMP_RNDN);        /* exp(x)*/
+      mpfr_sub_ui(t,te,1,GMP_RNDN);   /* exp(x)-1 */
+
+      /* estimation of the error */
+      err=Nt-(_mpfr_ceil_log2(1+pow(2,MPFR_EXP(te)-MPFR_EXP(t))));
+
+      /* actualisation of the precision */
+      Nt += 10;
+
+    } while (!mpfr_can_round(t,err,GMP_RNDN,rnd_mode,Ny));
+ 
+      inexact = mpfr_set(y,t,rnd_mode);
+
+      mpfr_clear(t);
+  }
+  return inexact;
+}