From 451904a0c5fae3bd28d35c7128df3a9db1a04b26 Mon Sep 17 00:00:00 2001
From: jaseg <git@jaseg.de>
Date: Thu, 26 Nov 2020 12:38:52 +0100
Subject: Add CRC32 implementation

---
 prototype/fw/src/crc32.c      | 35 +++++++++++++++++++++++++++++++++++
 prototype/fw/src/crc32.h      | 12 ++++++++++++
 prototype/fw/src/crc32_test.c | 20 ++++++++++++++++++++
 3 files changed, 67 insertions(+)
 create mode 100644 prototype/fw/src/crc32.c
 create mode 100644 prototype/fw/src/crc32.h
 create mode 100644 prototype/fw/src/crc32_test.c

(limited to 'prototype/fw/src')

diff --git a/prototype/fw/src/crc32.c b/prototype/fw/src/crc32.c
new file mode 100644
index 0000000..4b03fbb
--- /dev/null
+++ b/prototype/fw/src/crc32.c
@@ -0,0 +1,35 @@
+#include "crc32.h"
+#include <unistd.h>
+
+/* Polynomial: 0xEDB88320 */
+
+/* python3:
+ * In [26]: apply = lambda st: ((st>>1) ^ 0xEDB88320) if (st & 1) else (st>>1)
+ * In [27]: print(',\n'.join([ '0x{:08x}'.format(apply(apply(apply(apply(x))))) for x in range(16) ]))
+ */
+uint32_t crc32_table[16] = {
+	0x00000000,
+	0x1db71064,
+	0x3b6e20c8,
+	0x26d930ac,
+	0x76dc4190,
+	0x6b6b51f4,
+	0x4db26158,
+	0x5005713c,
+	0xedb88320,
+	0xf00f9344,
+	0xd6d6a3e8,
+	0xcb61b38c,
+	0x9b64c2b0,
+	0x86d3d2d4,
+	0xa00ae278,
+	0xbdbdf21c
+};
+
+crc32_t crc32_update(crc32_t state, uint8_t c)
+{
+	state ^= c;
+	state = (state>>4) ^ crc32_table[state&0xf];
+	state = (state>>4) ^ crc32_table[state&0xf];
+	return state;
+}
diff --git a/prototype/fw/src/crc32.h b/prototype/fw/src/crc32.h
new file mode 100644
index 0000000..7a3a729
--- /dev/null
+++ b/prototype/fw/src/crc32.h
@@ -0,0 +1,12 @@
+#ifndef __CRC_32_H__
+#define __CRC_32_H__
+
+#include <stdint.h>
+
+typedef uint32_t crc32_t;
+
+inline static uint32_t crc32_reset() { return ~0; }
+uint32_t crc32_update(uint32_t old_state, uint8_t c);
+inline static uint32_t crc32_finalize(uint32_t state) { return ~state; }
+
+#endif /* __CRC_32_H__ */
diff --git a/prototype/fw/src/crc32_test.c b/prototype/fw/src/crc32_test.c
new file mode 100644
index 0000000..e23bb37
--- /dev/null
+++ b/prototype/fw/src/crc32_test.c
@@ -0,0 +1,20 @@
+
+#include <stdio.h>
+
+#include "crc32.h"
+
+int main(void) {
+	crc32_t state = crc32_reset();
+
+	do {
+		char c;
+		if (fread(&c, 1, 1, stdin) != 1)
+			break;
+
+		state = crc32_update(state, (uint8_t)c);
+	} while(23);
+
+	state = crc32_finalize(state);
+	printf("%08x\n", state);
+	return 0;
+}
-- 
cgit