lib: Add CRC-8 and CRC-16 checksums

These checksum will be handy for header checksums.

Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>

1 files changed, 64 insertions, 0 deletions

diff --git a/src/lib/crc8.c b/src/lib/crc8.c
new file mode 100644
index 00000000..e8b9685a
--- /dev/null
+++ b/src/lib/crc8.c
@@ -0,0 +1,64 @@
+/*
+ * Ouroboros - Copyright (C) 2016 - 2026
+ *
+ * 8-bit Cyclic Redundancy Check (AUTOSAR variant)
+ *
+ *    Dimitri Staessens <dimitri@ouroboros.rocks>
+ *    Sander Vrijders   <sander@ouroboros.rocks>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * version 2.1 as published by the Free Software Foundation.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., http://www.fsf.org/about/contact/.
+ */
+
+/*
+ * CRC-8/AUTOSAR (reveng catalog):
+ *   poly   = 0x2f
+ *   init   = 0xff
+ *   refin  = false
+ *   refout = false
+ *   xorout = 0xff
+ *   check  = crc8_autosar("123456789") == 0xdf
+ */
+
+#include "config.h"
+
+#include <ouroboros/crc8.h>
+
+/* Bit-by-bit MSB-first CRC.  The expected use case is header check
+ * sequences of a handful of bytes; a 256-byte lookup table would not
+ * pay for the extra .rodata footprint at typical input sizes.
+ */
+void crc8_autosar(uint8_t *    crc,
+                  const void * buf,
+                  size_t       len)
+{
+        const uint8_t * p;
+        uint8_t         c;
+        size_t          n;
+        int             i;
+
+        p = (const uint8_t *) buf;
+        c = *crc ^ 0xff;
+
+        for (n = 0; n < len; n++) {
+                c ^= p[n];
+                for (i = 0; i < 8; i++) {
+                        if (c & 0x80)
+                                c = (uint8_t) ((c << 1) ^ 0x2f);
+                        else
+                                c = (uint8_t) (c << 1);
+                }
+        }
+
+        *crc = c ^ 0xff;
+}