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authorjaseg <git@jaseg.de>2023-10-02 01:23:31 +0200
committerjaseg <git@jaseg.de>2023-10-02 01:23:31 +0200
commitc8623eb4c6c1464ffd49e83126e66d71ba5bf862 (patch)
tree55151e10f1ca05f2539de59778e757819038678e /common/crc32.c
parent67e30fa91e12b452c1a18f6c5eb8a33cdb9ec625 (diff)
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Diffstat (limited to 'common/crc32.c')
-rw-r--r--common/crc32.c34
1 files changed, 34 insertions, 0 deletions
diff --git a/common/crc32.c b/common/crc32.c
new file mode 100644
index 0000000..3f8d128
--- /dev/null
+++ b/common/crc32.c
@@ -0,0 +1,34 @@
+#include "crc32.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) ]))
+ */
+static uint32_t crc32_table[16] = {
+ 0x00000000,
+ 0x1db71064,
+ 0x3b6e20c8,
+ 0x26d930ac,
+ 0x76dc4190,
+ 0x6b6b51f4,
+ 0x4db26158,
+ 0x5005713c,
+ 0xedb88320,
+ 0xf00f9344,
+ 0xd6d6a3e8,
+ 0xcb61b38c,
+ 0x9b64c2b0,
+ 0x86d3d2d4,
+ 0xa00ae278,
+ 0xbdbdf21c
+};
+
+uint32_t crc32_update(uint32_t state, uint8_t c)
+{
+ state ^= c;
+ state = (state>>4) ^ crc32_table[state&0xf];
+ state = (state>>4) ^ crc32_table[state&0xf];
+ return state;
+}