1 files changed, 25 insertions, 0 deletions
diff --git a/src/getsum.c b/src/getsum.c
new file mode 100644
index 0000000..b92fdef
--- /dev/null
+++ b/src/getsum.c
@@ -0,0 +1,25 @@
+/*
+	Copyright 2022-2023 Gabriel Jensen.
+
+	This file is part of agbsum.
+	agbsum is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
+	agbsum is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.
+	You should have received a copy of the GNU Affero General Public License along with agbsum. If not, see <https://www.gnu.org/licenses/>.
+*/
+
+#include <agbsum.h>
+
+#include <stdint.h>
+
+uint8_t
+agb_getsum (void const* const restrict romptr)
+{
+	uint8_t const* restrict rom    = romptr;
+	uint8_t                 chksum = 0x0u;
+
+	for (unsigned char const* restrict pos = rom;pos != rom+agb_chksumoff;++pos) {chksum += *pos;}
+
+	chksum = 0x0u-(0x19u+chksum);
+
+	return chksum;
+}