From 06696f40afe58a231e2531c8bf6d9f0dadb92e51 Mon Sep 17 00:00:00 2001
From: Jakob Kaivo <jkk@ung.org>
Date: Sun, 3 Mar 2019 21:25:50 -0500
Subject: outline details from C18 annex F

---
 src/math/round.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

(limited to 'src/math/round.c')

diff --git a/src/math/round.c b/src/math/round.c
index c154bdbf..5eedd578 100644
--- a/src/math/round.c
+++ b/src/math/round.c
@@ -1,10 +1,33 @@
 # define TGSOURCE "round.c"
 #include "_tgmath.h"
 #include <math.h>
+#include "fenv.h"
+
+#ifndef __GNUC__
+#pragma STDC FENV_ACCESS ON
+#endif
 
 TYPE TGFN(round)(TYPE x)
 {
-	return x;
+	switch (fpclassify(x)) {
+	case FP_ZERO:		return x;
+	case FP_INFINITE:	return x;
+	default:		break;
+	}
+
+	fenv_t save_env;
+	feholdexcept(&save_env);
+
+	TYPE ret = TGFN(rint)(x);
+
+	if (fetestexcept(FE_INEXACT)) {
+		fesetround(FE_TOWARDZERO);
+		ret = TGFN(rint)(TGFN(copysign)(0.5 + TGFN(fabs)(x), x));
+	}
+
+	feupdateenv(&save_env);
+
+	return ret;
 }
 
 /*
-- 
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