Add preliminary generic code to handle cached const.

Move const_pi, const_log2 to use this generic cache,
which fix bugs of the previous implementation.
const_euler is now cached too.


git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@2876 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 112 insertions, 0 deletions

diff --git a/cache.c b/cache.c
new file mode 100644
index 000000000..13546ae9d
--- /dev/null
+++ b/cache.c
@@ -0,0 +1,112 @@
+/* mpfr_cache -- cache interface for multi-precision const in MPFR.
+
+Copyright 2004 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 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 "mpfr-impl.h"
+
+/* Global MPFR cache */
+MPFR_DECL_INIT_CACHE(__gmpfr_cache_const_pi, mpfr_const_pi);
+MPFR_DECL_INIT_CACHE(__gmpfr_cache_const_log2, mpfr_const_log2);
+MPFR_DECL_INIT_CACHE(__gmpfr_cache_const_euler, mpfr_const_euler);
+
+void
+mpfr_init_cache (mpfr_cache_t cache, int (*func)(mpfr_ptr, mp_rnd_t))
+{
+  MPFR_PREC (cache->x) = 0; /* Invalid prec to detect that the cache is not
+			       valid. Maybe add a flag? */
+  cache->func = func;
+}
+
+void
+mpfr_clear_cache (mpfr_cache_t cache)
+{
+  if (MPFR_PREC(cache->x) != 0)
+    mpfr_clear (cache->x);
+  MPFR_PREC(cache->x) = 0;
+}
+
+int
+mpfr_cache (mpfr_ptr dest, mpfr_cache_t cache, mp_rnd_t rnd)
+{
+  mp_prec_t prec = MPFR_PREC (dest);
+  mp_prec_t pold = MPFR_PREC (cache->x);
+  int inexact;
+
+  /* Check if the cache has been already filled */
+  if (MPFR_UNLIKELY(pold == 0))
+    mpfr_init2 (cache->x, MPFR_PREC_MIN);
+  
+  /* Check if we can round with the previous result */
+  else if (prec <= pold)
+    goto round;
+  
+  /* Update the cache */ 
+  pold = prec /*MPFR_PREC_MIN + prec + __gmpfr_ceil_exp2 (prec)*/;
+  MPFR_ASSERTD (pold >= prec);
+  mpfr_prec_round (cache->x, pold, GMP_RNDN);
+  cache->inexact = (*cache->func) (cache->x, GMP_RNDN);
+
+ round:
+  /* First check if the cache has the exact value (Unlikely)
+     Else the exact value is between (assuming x=cache->x > 0)
+     x and x+ulp(x) if cache->inexact < 0
+     x-ulp(x) and x if cache->inexact > 0 
+     and abs(x-exact) <= ulp(x)/2 */
+  MPFR_ASSERTD (MPFR_IS_POS(cache->x)); /* TODO...*/
+     
+  inexact = mpfr_set (dest, cache->x, rnd);
+  if (MPFR_LIKELY(cache->inexact != 0))
+    {
+      switch (rnd)
+	{
+	case GMP_RNDZ:
+	case GMP_RNDD:
+	  if (MPFR_UNLIKELY(inexact == 0))
+	    {
+              inexact = cache->inexact;
+	      if (inexact > 0)
+		mpfr_sub_one_ulp (dest, rnd);
+	    }
+	  break;
+	case GMP_RNDU:
+          if (MPFR_UNLIKELY(inexact == 0))
+            {
+              inexact = cache->inexact;
+              if (inexact < 0)
+                mpfr_add_one_ulp (dest, rnd);
+            }
+          break;
+	default: /* GMP_RNDN */
+	  if (MPFR_UNLIKELY(inexact == MPFR_EVEN_INEX ||
+			    inexact == -MPFR_EVEN_INEX))
+	    {
+	      if (cache->inexact < 0)
+		mpfr_add_one_ulp (dest, rnd);
+	      else
+		mpfr_sub_one_ulp (dest, rnd);
+	      inexact = -inexact;
+	    }
+	  else if (MPFR_UNLIKELY(inexact == 0))
+	    inexact = cache->inexact;
+	  break;
+	}
+    }
+  return inexact;
+}