[src/sub1sp.c] simplified code of sub1sp1 for bx = cx

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@13511 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 7 insertions, 18 deletions

diff --git a/src/sub1sp.c b/src/sub1sp.c
index 51bd33b83..a8c39a266 100644
--- a/src/sub1sp.c
+++ b/src/sub1sp.c
@@ -120,13 +120,7 @@ mpfr_sub1sp1 (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mpfr_rnd_t rnd_mode,
 
   if (bx == cx)
     {
-      MPFR_ASSERTD (bp[0] >= MPFR_LIMB_HIGHBIT);
-      MPFR_ASSERTD (cp[0] >= MPFR_LIMB_HIGHBIT);
-      /* Thus, mathematically, the signed difference is between
-         1 - MPFR_LIMB_HIGHBIT and MPFR_LIMB_HIGHBIT - 1, and the
-         most significant bit is equivalent to the usual sign bit. */
-      a0 = bp[0] - cp[0];
-      if (a0 == 0) /* result is zero */
+      if (MPFR_UNLIKELY(bp[0] == cp[0])) /* result is zero */
         {
           if (rnd_mode == MPFR_RNDD)
             MPFR_SET_NEG(a);
@@ -135,21 +129,16 @@ mpfr_sub1sp1 (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mpfr_rnd_t rnd_mode,
           MPFR_SET_ZERO(a);
           MPFR_RET (0);
         }
-      else if (a0 >= MPFR_LIMB_HIGHBIT) /* borrow: |c| > |b| */
+      else if (cp[0] > bp[0]) /* borrow: |c| > |b| */
         {
-          /* Note: The test before r13506 was a0 > bp[0], which should be
-             easier to optimize than a0 >= MPFR_LIMB_HIGHBIT on processors
-             with condition flags, i.e. the test should be a no-op as the
-             flag should have been obtained from the subtraction above.
-             See <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=30315>.
-             As of version 7, Clang knows to optimize the a0 > bp[0].
-             TODO: revert the test in the future, once compilers have
-             improved? */
+          a0 = cp[0] - bp[0];
           MPFR_SET_OPPOSITE_SIGN (a, b);
-          a0 = -a0;
         }
       else /* bp[0] > cp[0] */
-        MPFR_SET_SAME_SIGN (a, b);
+        {
+          a0 = bp[0] - cp[0];
+          MPFR_SET_SAME_SIGN (a, b);
+        }
 
       /* now a0 != 0 */
       MPFR_ASSERTD(a0 != 0);