Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library; if not, write to the Free
- Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
- 02111-1307 USA. */
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
#include "quadmath-imp.h"
#include <math.h>
underflows to 0. */
if (z == 0 && x != 0 && y != 0)
return x * y;
- /* If x or y or z is Inf/NaN, or if fma will certainly overflow,
- or if x * y is less than half of FLT128_DENORM_MIN,
- compute as x * y + z. */
+ /* If x or y or z is Inf/NaN, or if x * y is zero, compute as
+ x * y + z. */
if (u.ieee.exponent == 0x7fff
|| v.ieee.exponent == 0x7fff
|| w.ieee.exponent == 0x7fff
- || u.ieee.exponent + v.ieee.exponent
- > 0x7fff + IEEE854_FLOAT128_BIAS
- || u.ieee.exponent + v.ieee.exponent
- < IEEE854_FLOAT128_BIAS - FLT128_MANT_DIG - 2)
+ || x == 0
+ || y == 0)
return x * y + z;
+ /* If fma will certainly overflow, compute as x * y. */
+ if (u.ieee.exponent + v.ieee.exponent
+ > 0x7fff + IEEE854_FLOAT128_BIAS)
+ return x * y;
/* If x * y is less than 1/4 of FLT128_DENORM_MIN, neither the
result nor whether there is underflow depends on its exact
value, only on its sign. */
{
/* Similarly.
If z exponent is very large and x and y exponents are
- very small, it doesn't matter if we don't adjust it. */
- if (u.ieee.exponent > v.ieee.exponent)
+ very small, adjust them up to avoid spurious underflows,
+ rather than down. */
+ if (u.ieee.exponent + v.ieee.exponent
+ <= IEEE854_FLOAT128_BIAS + FLT128_MANT_DIG)
+ {
+ if (u.ieee.exponent > v.ieee.exponent)
+ u.ieee.exponent += 2 * FLT128_MANT_DIG + 2;
+ else
+ v.ieee.exponent += 2 * FLT128_MANT_DIG + 2;
+ }
+ else if (u.ieee.exponent > v.ieee.exponent)
{
if (u.ieee.exponent > FLT128_MANT_DIG)
u.ieee.exponent -= FLT128_MANT_DIG;
if (__builtin_expect ((x == 0 || y == 0) && z == 0, 0))
return x * y + z;
+#ifdef USE_FENV_H
+ fenv_t env;
+ feholdexcept (&env);
+ fesetround (FE_TONEAREST);
+#endif
+
/* Multiplication m1 + m2 = x * y using Dekker's algorithm. */
#define C ((1LL << (FLT128_MANT_DIG + 1) / 2) + 1)
__float128 x1 = x * C;
t1 = m1 - t1;
t2 = z - t2;
__float128 a2 = t1 + t2;
+#ifdef USE_FENV_H
+ feclearexcept (FE_INEXACT);
+#endif
+
+ /* If the result is an exact zero, ensure it has the correct
+ sign. */
+ if (a1 == 0 && m2 == 0)
+ {
+#ifdef USE_FENV_H
+ feupdateenv (&env);
+#endif
+ /* Ensure that round-to-nearest value of z + m1 is not
+ reused. */
+ asm volatile ("" : "=m" (z) : "m" (z));
+ return z + m1;
+ }
+
#ifdef USE_FENV_H
- fenv_t env;
- feholdexcept (&env);
fesetround (FE_TOWARDZERO);
#endif
/* Perform m2 + a2 addition with round to odd. */