outline details from C18 annex F

1 files changed, 16 insertions, 0 deletions

diff --git a/src/math/log2.c b/src/math/log2.c
index c438d7ce..55569065 100644
--- a/src/math/log2.c
+++ b/src/math/log2.c
@@ -1,9 +1,25 @@
 #define TGSOURCE "log2.c"
 #include "_tgmath.h"
 #include <math.h>
+#include "fenv.h"
 
 TYPE TGFN(log2)(TYPE x)
 {
+	switch (fpclassify(x)) {
+	case FP_ZERO:		feraiseexcept(FE_DIVBYZERO); return - INFINITY;
+	case FP_INFINITE:	if (!signbit(x)) { return x; } break;
+	default:		break;
+	}
+
+	if (x == 1.0) {
+		return 0.0;
+	}
+
+	if (x < 0.0) {
+		feraiseexcept(FE_INVALID);
+		return NAN;
+	}
+
 	return x;
 }