11175 libm should use signbit() correctly
11188 c99 math macros should return strictly backward compatible values

*** 71,91 ****
          PIo2    =  1.570796326794896619231321691639751442099L,
          PI      =  3.141592653589793238462643383279502884197L,
          PI_lo   =  8.671810130123781024797044026043351968762e-35L;
  
  long double
! atan2l(long double y, long double x) {
          long double t, z;
          int k, m, signy, signx;
  
          if (x != x || y != y)
                  return (x + y); /* return NaN if x or y is NAN */
          signy = signbitl(y);
          signx = signbitl(x);
          if (x == one)
                  return (atanl(y));
!         m = signy + signx + signx;
  
          /* when y = 0 */
          if (y == zero)
                  switch (m) {
                  case 0:
--- 71,93 ----
          PIo2    =  1.570796326794896619231321691639751442099L,
          PI      =  3.141592653589793238462643383279502884197L,
          PI_lo   =  8.671810130123781024797044026043351968762e-35L;
  
  long double
! atan2l(long double y, long double x)
! {
          long double t, z;
          int k, m, signy, signx;
  
          if (x != x || y != y)
                  return (x + y); /* return NaN if x or y is NAN */
          signy = signbitl(y);
          signx = signbitl(x);
          if (x == one)
                  return (atanl(y));
!         /* Ensure sign indicators are boolean */
!         m = (signy != 0) + (signx != 0) + (signx != 0);
  
          /* when y = 0 */
          if (y == zero)
                  switch (m) {
                  case 0:
*** 98,108 ****
                          return (-PI - tiny);    /* atan(-0,-anything) */
                  }
  
          /* when x = 0 */
          if (x == zero)
!                 return (signy == 1 ? -PIo2 - tiny : PIo2 + tiny);
  
          /* when x is INF */
          if (!finitel(x)) {
                  if (!finitel(y)) {
                          switch (m) {
--- 100,110 ----
                          return (-PI - tiny);    /* atan(-0,-anything) */
                  }
  
          /* when x = 0 */
          if (x == zero)
!                 return (signy != 0 ? -PIo2 - tiny : PIo2 + tiny);
  
          /* when x is INF */
          if (!finitel(x)) {
                  if (!finitel(y)) {
                          switch (m) {
*** 128,138 ****
                          }
                  }
          }
          /* when y is INF */
          if (!finitel(y))
!                 return (signy == 1 ? -PIo2 - tiny : PIo2 + tiny);
  
          /* compute y/x */
          x = fabsl(x);
          y = fabsl(y);
          t = PI_lo;
--- 130,140 ----
                          }
                  }
          }
          /* when y is INF */
          if (!finitel(y))
!                 return (signy != 0 ? -PIo2 - tiny : PIo2 + tiny);
  
          /* compute y/x */
          x = fabsl(x);
          y = fabsl(y);
          t = PI_lo;
*** 154,160 ****
                  return (PI - (z - t));  /* atan(+,-) */
          case 3:
                  return ((z - t) - PI);  /* atan(-,-) */
          }
          /* NOTREACHED */
!     return 0.0L;
  }
--- 156,162 ----
                  return (PI - (z - t));  /* atan(+,-) */
          case 3:
                  return ((z - t) - PI);  /* atan(-,-) */
          }
          /* NOTREACHED */
!         return (0.0L);
  }