From 434e61c231e142b6f5f8d81eb25f4ef97686d85a Mon Sep 17 00:00:00 2001
From: Robin Krahl <robin.krahl@ireas.org>
Date: Sat, 27 Mar 2021 16:10:53 +0100
Subject: Initial commit

---
 src/crc32.rs | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 src/crc32.rs

(limited to 'src/crc32.rs')

diff --git a/src/crc32.rs b/src/crc32.rs
new file mode 100644
index 0000000..6b3f9d7
--- /dev/null
+++ b/src/crc32.rs
@@ -0,0 +1,84 @@
+// https://github.com/d-e-s-o/nitrocli/blob/ac29709a644682c61a5a28d2a23f8887174fcc31/nitrocli/src/crc32.rs
+//
+// *************************************************************************
+// * Copyright (C) 2017 Daniel Mueller (deso@posteo.net)                   *
+// *                                                                       *
+// * This program 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.                                   *
+// *                                                                       *
+// * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>. *
+// *************************************************************************
+
+/// Polynomial used in STM32.
+const CRC32_POLYNOMIAL: u32 = 0x04c11db7;
+
+fn crc32(mut crc: u32, data: u32) -> u32 {
+    crc = crc ^ data;
+
+    for _ in 0..32 {
+        if crc & 0x80000000 != 0 {
+            crc = (crc << 1) ^ CRC32_POLYNOMIAL;
+        } else {
+            crc = crc << 1;
+        }
+    }
+    return crc;
+}
+
+/// Retrieve a u32 slice of the 'data' part.
+///
+/// Note that the size of the supplied data has to be a multiple of 4
+/// bytes.
+fn as_slice_u32(data: &[u8]) -> &[u32] {
+    assert!(data.len() % ::std::mem::size_of::<u32>() == 0);
+
+    unsafe {
+        let ptr = data.as_ptr() as *const u32;
+        let len = data.len() / ::std::mem::size_of::<u32>();
+        return ::std::slice::from_raw_parts(ptr, len);
+    }
+}
+
+/// Calculate the CRC of a byte slice.
+pub fn crc(data: &[u8]) -> u32 {
+    let mut crc = 0xffffffff;
+
+    for value in as_slice_u32(data) {
+        crc = crc32(crc, *value);
+    }
+
+    return crc;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_crc32() {
+        let mut crc = 0;
+
+        // The expected values were computed with the original function.
+        crc = crc32(crc, 0xdeadbeef);
+        assert_eq!(crc, 0x46dec763);
+
+        crc = crc32(crc, 42);
+        assert_eq!(crc, 0x7e579b45);
+    }
+
+    #[test]
+    fn test_crc() {
+        let data = &"thisisatextthatistobecrced..".to_string().into_bytes();
+        let crc = crc(data);
+
+        assert_eq!(crc, 0x469db4ee);
+    }
+}
-- 
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