From fb08628f17893280da43c70f0919687feca09265 Mon Sep 17 00:00:00 2001
From: daurnimator <quae@daurnimator.com>
Date: Sun, 15 Nov 2015 20:44:09 +1100
Subject: Implement lua rounding style for __mod operator

---
 src/openssl.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/openssl.c b/src/openssl.c
index 9dbcda7..69115ce 100644
--- a/src/openssl.c
+++ b/src/openssl.c
@@ -1809,6 +1809,12 @@ static int bn__mod(lua_State *L) {
 	if (!BN_mod(r, a, b, getctx(L)))
 		return auxL_error(L, auxL_EOPENSSL, "bignum:__mod");
 
+	/* lua has different rounding behaviour for mod than C */
+	if (!BN_is_zero(r) && (BN_is_negative(a) ^ BN_is_negative(b))) {
+		if (!BN_add(r, r, b))
+			return auxL_error(L, auxL_EOPENSSL, "bignum:__mod");
+	}
+
 	return 1;
 } /* bn__mod() */
 
-- 
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