AP_Common: Added missing fenv exception functions from FreeBSD fenv tree

Signed-off-by: Sandy Urazayev <ctu@ku.edu>

libraries/AP_Common/missing/fenv.h

@@ -4,6 +4,7 @@
 
 #ifndef HAVE_FEENABLEEXCEPT
 #if defined(__APPLE__) && defined(__MACH__)
+#if defined __i386__ || defined __x86_64__
 
 // Public domain polyfill for feenableexcept on OS X
 // http://www-personal.umich.edu/~williams/archive/computation/fe-handling-example.c
@@ -46,6 +47,70 @@ inline int fedisableexcept(unsigned int excepts)
     return fesetenv(&fenv) ? -1 : old_excepts;
 }
 
+#elif defined __arm64__
+
+/*
+  Yoinked and adapted this ARM64 implementation of floating point exceptions from
+  https://android.googlesource.com/platform/bionic/+/a147a1d/libm/arm64/fenv.c
+ */
+
+/*-
+ * Copyright (c) 2004 David Schultz <das@FreeBSD.ORG>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD: libm/aarch64/fenv.c $
+ */
+
+
+#define FPCR_EXCEPT_SHIFT 8
+
+// FPCR, Floating-point Control Register.
+#define __get_fpcr(__fpcr) __asm__ __volatile__("mrs %0,fpcr" : "=r" (__fpcr))
+#define __set_fpcr(__fpcr) __asm__ __volatile__("msr fpcr,%0" : :"ri" (__fpcr))
+
+inline int feenableexcept(int mask) {
+    unsigned long long old_fpcr, new_fpcr;
+    __get_fpcr(old_fpcr);
+    new_fpcr = old_fpcr | ((mask & FE_ALL_EXCEPT) << FPCR_EXCEPT_SHIFT);
+    if (new_fpcr != old_fpcr) {
+        __set_fpcr(new_fpcr);
+    }
+    return ((old_fpcr >> FPCR_EXCEPT_SHIFT) & FE_ALL_EXCEPT);
+}
+
+inline int fedisableexcept(int mask) {
+    unsigned long long old_fpcr, new_fpcr;
+    __get_fpcr(old_fpcr);
+    new_fpcr = old_fpcr & ~((mask & FE_ALL_EXCEPT) << FPCR_EXCEPT_SHIFT);
+    if (new_fpcr != old_fpcr) {
+        __set_fpcr(new_fpcr);
+    }
+    return ((old_fpcr >> FPCR_EXCEPT_SHIFT) & FE_ALL_EXCEPT);
+}
+
+#endif
+
 #else
 inline int feenableexcept(unsigned int excepts)
 {