Add a macro STRICT_ASSIGN() to help avoid the compiler bug that

assignments and casts don't clip extra precision, if any.  The
implementation is to assign to a temporary volatile variable and read
the result back to assign to the original lvalue.

lib/msun currently 2 different hard-coded hacks to avoid the problem
in just a few places and needs it in a few more places.  One variant
uses volatile for the original lvalue.  This works but is slower than
necessary.  Another temporarily casts the lvalue to volatile.  This
broke with gcc-4.2.1 or earlier (gcc now stores to the lvalue but
doesn't load from it).

1 files changed, 16 insertions, 0 deletions

diff --git a/lib/msun/src/math_private.h b/lib/msun/src/math_private.h
index 2db3c02..15ef4fb 100644
--- a/lib/msun/src/math_private.h
+++ b/lib/msun/src/math_private.h
@@ -154,6 +154,22 @@ do {								\
   (d) = sf_u.value;						\
 } while (0)
 
+#ifdef FLT_EVAL_METHOD
+/*
+ * Attempt to get strict C99 semantics for assignment with non-C99 compilers.
+ */
+#if FLT_EVAL_METHOD == 0 || __GNUC__ == 0
+#define	STRICT_ASSIGN(type, lval, rval)	((lval) = (rval))
+#else
+#define	STRICT_ASSIGN(type, lval, rval) do {	\
+	volatile type __lval;			\
+						\
+	__lval = (rval);			\
+	(lval) = __lval;			\
+} while (0)
+#endif
+#endif
+
 /*
  * Common routine to process the arguments to nan(), nanf(), and nanl().
  */