[Patch, Fortran] PR52413 - Incorrect behavior of FRACTION when applied to a constant

[Dominique Dhumieres]

This patch packages the Steven G. Kargl's patch when MPFR 3.1.0 or newer 
is available and fixes the original code for older versions using the 
FX Coudert's machinery (see PR for details).

Tested on powerpc-apple-darwin9 and x86_64-apple-darwin10 without 
regression.

OK for the trunk? If yes, could someone commit it for me?

Since this is a wrong-code issue, I think the light version of the patch 
should be applied to 4.7 and 4.8. If this is accepted I'll do the testing 
and the packaging.

Dominique


2013-06-23  Steven G. Kargl  <s...@troutmask.apl.washington.edu>
            Francois-Xavier Coudert  <fxcoud...@gcc.gnu.org>
            Dominique d'Humieres  <domi...@lps.ens.fr>

        PR fortran/52413
        * simplify.c: Fix the sign of negative values in gfc_simplify_fraction.

2013-06-23  Francois-Xavier Coudert  <fxcoud...@gcc.gnu.org>
            Dominique d'Humieres  <domi...@lps.ens.fr>

        PR fortran/52413
        * gfortran.dg/fraction.f90: New.


--- ../_clean/gcc/fortran/simplify.c    2013-06-08 21:50:33.000000000 +0200
+++ gcc/fortran/simplify.c      2013-06-23 17:19:55.000000000 +0200
@@ -2342,16 +2342,26 @@ gfc_expr *
 gfc_simplify_fraction (gfc_expr *x)
 {
   gfc_expr *result;
+
+#if MPFR_VERSION < MPFR_VERSION_NUM(3,1,0)
   mpfr_t absv, exp, pow2;
+#else
+  mpfr_exp_t e;
+#endif
 
   if (x->expr_type != EXPR_CONSTANT)
     return NULL;
 
   result = gfc_get_constant_expr (BT_REAL, x->ts.kind, &x->where);
 
+#if MPFR_VERSION < MPFR_VERSION_NUM(3,1,0)
+
+  /* MPFR versions before 3.1.0 do not include mpfr_frexp.  
+     TODO: remove the kludge when MPFR 3.1.0 or newer will be required */
+
   if (mpfr_sgn (x->value.real) == 0)
     {
-      mpfr_set_ui (result->value.real, 0, GFC_RND_MODE);
+      mpfr_set (result->value.real, x->value.real, GFC_RND_MODE);
       return result;
     }
 
@@ -2368,10 +2378,16 @@ gfc_simplify_fraction (gfc_expr *x)
 
   mpfr_ui_pow (pow2, 2, exp, GFC_RND_MODE);
 
-  mpfr_div (result->value.real, absv, pow2, GFC_RND_MODE);
+  mpfr_div (result->value.real, x->value.real, pow2, GFC_RND_MODE);
 
   mpfr_clears (exp, absv, pow2, NULL);
 
+#else
+
+  mpfr_frexp (&e, result->value.real, x->value.real, GFC_RND_MODE);
+
+#endif
+
   return range_check (result, "FRACTION");
 }
 
--- ../_clean/gcc/testsuite/gfortran.dg/fraction.f90    1970-01-01 
01:00:00.000000000 +0100
+++ gcc/testsuite/gfortran.dg/fraction.f90      2013-06-23 22:06:00.000000000 
+0200
@@ -0,0 +1,15 @@
+! { dg-do run }
+!
+! Test for pr52413
+!
+
+program test_frac
+
+  real :: y
+  y=fraction (-2.0) 
+  if (fraction (-2.0) /= -0.5) call abort ()
+  if (fraction (-0.0) /= 0.0) call abort ()
+  if (sign(1.0, fraction(-0.0)) /= -1.0) call abort ()
+  if (fraction (-2.0_8) /=  -0.5) call abort ()
+
+end program test_frac