5224 snprintf rounding under [default] FE_TONEAREST

*** 36,48 ****
   */
  double
  __mul_set(double x, double y, int *pe) {
          extern void _putsw(), _getsw();
          int sw;
!         double z;
  
          _putsw(0);
          z = x * y;
          _getsw(&sw);
          if ((sw & 0x3f) == 0) {
                  *pe = 0;
          } else {
--- 36,62 ----
   */
  double
  __mul_set(double x, double y, int *pe) {
          extern void _putsw(), _getsw();
          int sw;
!         volatile double z;
  
          _putsw(0);
+         /*
+          * NOTE:  By declaring 'z' volatile above, we intend for the
+          * compiler to not move this after the _getmxcsr() call, whose results
+          * are only useful if they immediately follow the multiply.
+          *
+          * From the C11 spec:
+          *
+          * 134 - A volatile declaration may be used to describe an
+          * object corresponding to a memory-mapped input/output port
+          * or an object accessed by an asynchronously interrupting
+          * function. Actions on objects so declared shall by an
+          * implementation or reordered except as permitted by the
+          * rules for evaluating expressions."
+          */
          z = x * y;
          _getsw(&sw);
          if ((sw & 0x3f) == 0) {
                  *pe = 0;
          } else {
*** 57,69 ****
   */
  double
  __div_set(double x, double y, int *pe) {
          extern void _putsw(), _getsw();
          int sw;
!         double z;
  
          _putsw(0);
          z = x / y;
          _getsw(&sw);
          if ((sw & 0x3f) == 0) {
                  *pe = 0;
          } else {
--- 71,84 ----
   */
  double
  __div_set(double x, double y, int *pe) {
          extern void _putsw(), _getsw();
          int sw;
!         volatile double z;
  
          _putsw(0);
+         /* NOTE:  See __mul_set() above, same principle applies here. */
          z = x / y;
          _getsw(&sw);
          if ((sw & 0x3f) == 0) {
                  *pe = 0;
          } else {