when recomputing a constant, use a precision 10% larger than the wanted

precision to avoid many recomputations


git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@8966 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 4 insertions, 2 deletions

diff --git a/src/cache.c b/src/cache.c
index a9b0602e7..a054682a2 100644
--- a/src/cache.c
+++ b/src/cache.c
@@ -60,8 +60,10 @@ mpfr_cache (mpfr_ptr dest, mpfr_cache_t cache, mpfr_rnd_t rnd)
       if (MPFR_UNLIKELY (pold == 0))  /* No previous result. */
         mpfr_init2 (cache->x, prec);
 
-      /* Update the cache. */
-      pold = prec;
+      /* Update the cache. We add prec/10 to avoid invalidating the cache
+         many times if one performs several computations with increasing
+         precision. */
+      pold = prec + (prec / 10);
       /* no need to keep the previous value */
       mpfr_set_prec (cache->x, pold);
       cache->inexact = (*cache->func) (cache->x, MPFR_RNDN);