More consistent excess precision handling

The current code aims to support FLT_EVAL_METHOD!=0 targets (such as
i386 with x87 fpu or m68k) assuming appropriate narrowing eval functions
are defined for them.  But the narrowing eval functions were not used
consistently: the return statement may not guarantee narrowing (e.g.
that was the C99 behaviour which got changed in C11 annex F) so we
should use the narrowing eval_as_ functions at return statements too.

Results should be correct if narrowing only happens at eval_as_ calls.
On most targets this change has no effect because eval_as_ is a noop.
Most math implementations that care about excess precision already
compile in a mode that narrows at returns so this change is not
necessary for them, just better documents the assumptions.

1 files changed, 3 insertions, 3 deletions

diff --git a/math/exp.c b/math/exp.c
index fa913b4..ffd3111 100644
--- a/math/exp.c
+++ b/math/exp.c
@@ -39,7 +39,7 @@ specialcase (double_t tmp, uint64_t sbits, uint64_t ki)
       sbits -= 1009ull << 52;
       scale = asdouble (sbits);
       y = 0x1p1009 * (scale + scale * tmp);
-      return check_oflow (y);
+      return check_oflow (eval_as_double (y));
     }
   /* k < 0, need special care in the subnormal range.  */
   sbits += 1022ull << 52;
@@ -63,7 +63,7 @@ specialcase (double_t tmp, uint64_t sbits, uint64_t ki)
       force_eval_double (opt_barrier_double (0x1p-1022) * 0x1p-1022);
     }
   y = 0x1p-1022 * y;
-  return check_uflow (y);
+  return check_uflow (eval_as_double (y));
 }
 
 /* Top 12 bits of a double (sign and exponent bits).  */
@@ -149,7 +149,7 @@ exp_inline (double x, double xtail, int hastail)
   scale = asdouble (sbits);
   /* Note: tmp == 0 or |tmp| > 2^-200 and scale > 2^-739, so there
      is no spurious underflow here even without fma.  */
-  return scale + scale * tmp;
+  return eval_as_double (scale + scale * tmp);
 }
 
 double