common: Add the varint module.

[gps-watch.git] / src / common / varint.rs

diff --git a/src/common/varint.rs b/src/common/varint.rs
new file mode 100644 (file)
index 0000000..211f558
--- /dev/null
+++ b/src/common/varint.rs
@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2017 Tilman Sauerbeck (tilman at code-monkey de)
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+pub fn write_u32(buffer: &mut [u8], _n: u32) -> usize {
+    let shift = 7;
+    let mask = 1 << shift;
+    let mut offset = 0;
+    let mut n = _n;
+
+    while n >= mask {
+        let b = (n | mask) as u8;
+
+        buffer[offset] = b;
+        offset += 1;
+
+        n >>= shift;
+    }
+
+    buffer[offset] = n as u8;
+    offset += 1;
+
+    offset
+}
+
+pub fn write_s32(buffer: &mut [u8], n: i32) -> usize {
+    let u = (n << 1) ^ (n >> 31);
+
+    write_u32(buffer, u as u32)
+}