AP_Common: add replacements for fe control functions systems without them

libraries/AP_Common/missing/fenv.h

@@ -0,0 +1,42 @@
+#pragma once
+#include_next <fenv.h>
+
+#if defined(__APPLE__) && defined(__MACH__)
+
+// Public domain polyfill for feenableexcept on OS X
+// http://www-personal.umich.edu/~williams/archive/computation/fe-handling-example.c
+
+inline int
+feenableexcept (unsigned int excepts)
+{
+  static fenv_t fenv;
+  unsigned int new_excepts = excepts & FE_ALL_EXCEPT,
+               old_excepts;  // previous masks
+
+  if ( fegetenv (&fenv) ) return -1;
+  old_excepts = fenv.__control & FE_ALL_EXCEPT;
+
+  // unmask
+  fenv.__control &= ~new_excepts;
+  fenv.__mxcsr   &= ~(new_excepts << 7);
+
+  return ( fesetenv (&fenv) ? -1 : old_excepts );
+}
+
+inline int
+fedisableexcept (unsigned int excepts)
+{
+  static fenv_t fenv;
+  unsigned int new_excepts = excepts & FE_ALL_EXCEPT,
+               old_excepts;  // all previous masks
+
+  if ( fegetenv (&fenv) ) return -1;
+  old_excepts = fenv.__control & FE_ALL_EXCEPT;
+
+  // mask
+  fenv.__control |= new_excepts;
+  fenv.__mxcsr   |= new_excepts << 7;
+
+  return ( fesetenv (&fenv) ? -1 : old_excepts );
+}
+#endif // APPLE