Adding CRC routines (to be used later to detect config corruption)

lib/SCSI2SD/src/firmware/crc.c

@@ -0,0 +1,37 @@
+//	Copyright (C) 2020 Michael McMaster <michael@codesrc.com>
+//
+//	This file is part of SCSI2SD.
+//
+//	SCSI2SD is free software: you can redistribute it and/or modify
+//	it under the terms of the GNU General Public License as published by
+//	the Free Software Foundation, either version 3 of the License, or
+//	(at your option) any later version.
+//
+//	SCSI2SD 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 General Public License for more details.
+//
+//	You should have received a copy of the GNU General Public License
+//	along with SCSI2SD.  If not, see <http://www.gnu.org/licenses/>.
+#include "crc.h"
+
+// Use standard CRC-32 reversed poly
+#define POLYNOMIAL 0xEDB88320
+
+// Slow (but small) implementation that doesn't use lookup tables.
+uint32_t s2s_crc32(uint8_t* data, int len)
+{
+	uint32_t crc = 0xFFFFFFFF;
+	for (int i = 0; i < len; ++i)
+	{
+		uint32_t byte = data[i];
+		crc = crc ^ byte;
+		for (int j = 7; j >= 0; j--)
+		{
+			uint32_t mask = -(crc & 1);
+			crc = (crc >> 1) ^ (POLYNOMIAL & mask);
+		}
+	}
+	return ~crc;
+}

lib/SCSI2SD/src/firmware/crc.h

@@ -0,0 +1,24 @@
+//	Copyright (C) 2020 Michael McMaster <michael@codesrc.com>
+//
+//	This file is part of SCSI2SD.
+//
+//	SCSI2SD is free software: you can redistribute it and/or modify
+//	it under the terms of the GNU General Public License as published by
+//	the Free Software Foundation, either version 3 of the License, or
+//	(at your option) any later version.
+//
+//	SCSI2SD 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 General Public License for more details.
+//
+//	You should have received a copy of the GNU General Public License
+//	along with SCSI2SD.  If not, see <http://www.gnu.org/licenses/>.
+#ifndef S2S_CRC_H
+#define S2S_CRC_H
+
+#include <stdint.h>
+
+uint32_t s2s_crc32(uint8_t* data, int len);
+
+#endif