[src/{fits_u.h,fits_uintmax.c}] Fixed the mpfr_fits_u*_p functions,

  which incorrectly returned 0 ("doesn't fit") on negative arguments
  when the rounding to an integer was 0. The fits_uintmax.c file now
  uses fits_u.h for consistency.
[tests/tfits.c] Added tests, in particular for small negative op
  (triggering the above bug) and in non-RNDN rounding modes.
(merged changesets r8494,8501-8503 from the trunk)

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/branches/3.1@8684 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 11 insertions, 8 deletions

diff --git a/src/fits_u.h b/src/fits_u.h
index e4bd6a024..fe4de05c1 100644
--- a/src/fits_u.h
+++ b/src/fits_u.h
@@ -32,17 +32,20 @@ FUNCTION (mpfr_srcptr f, mpfr_rnd_t rnd)
   int res;
 
   if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (f)))
-    /* Zero always fit */
-    return MPFR_IS_ZERO (f) ? 1 : 0;
-  else if (MPFR_IS_NEG (f))
-    /* Negative numbers don't fit */
-    return 0;
-  /* now it fits if
-     (a) f <= MAXIMUM
-     (b) round(f, prec(slong), rnd) <= MAXIMUM */
+    return MPFR_IS_ZERO (f) ? 1 : 0;  /* Zero always fits */
 
   e = MPFR_GET_EXP (f);
 
+  if (MPFR_IS_NEG (f))
+    return e >= 1 ? 0  /* f <= -1 does not fit */
+      : rnd != MPFR_RNDN ? MPFR_IS_LIKE_RNDU (rnd, -1)  /* directed mode */
+      : e < 0 ? 1  /* f > -1/2 fits in MPFR_RNDN */
+      : mpfr_powerof2_raw(f);  /* -1/2 fits, -1 < f < -1/2 don't */
+
+  /* Now it fits if
+     (a) f <= MAXIMUM
+     (b) round(f, prec(slong), rnd) <= MAXIMUM */
+
   /* first compute prec(MAXIMUM); fits in an int */
   for (s = MAXIMUM, prec = 0; s != 0; s /= 2, prec ++);