outline details from C18 annex F

1 files changed, 8 insertions, 1 deletions

diff --git a/src/math/acos.c b/src/math/acos.c
index 2f740d03..9a356100 100644
--- a/src/math/acos.c
+++ b/src/math/acos.c
@@ -1,12 +1,15 @@
 # define TGSOURCE "acos.c"
 #include <math.h>
+#include "fenv.h"
 #include "errno.h"
 #include "_tgmath.h"
 
 /** arc cosine **/
 TYPE TGFN(acos)(TYPE x)
 {
-	if (x < -1 || x > 1) {
+	if (TGFN(fabs)(x) > 1) {
+		feraiseexcept(FE_INVALID);
+		return NAN;
 		errno = EDOM;	/* ARGUMENT(x) not in the range [-1, +1] */
 		return TGHUGE;
 	}
@@ -17,6 +20,10 @@ TYPE TGFN(acos)(TYPE x)
 		return TGHUGE;
 	}
 
+	if (x == 1.0) {
+		return 0.0;
+	}
+
 	/* RETURN_SUCCESS(a value in range `[0, PI()]'); */
 	return (TYPE)0.0;
 }