1 /// Reverse the first length bits of n.
2 /// (Passing more than 16 as length will produce garbage.
reverse_bits(mut n: u16, length: u8) -> u163 pub fn reverse_bits(mut n: u16, length: u8) -> u16 {
4     debug_assert!(length <= 16);
5     // Borrowed from http://aggregate.org/MAGIC/#Bit%20Reversal
6     n = ((n & 0xaaaa) >> 1) | ((n & 0x5555) << 1);
7     n = ((n & 0xcccc) >> 2) | ((n & 0x3333) << 2);
8     n = ((n & 0xf0f0) >> 4) | ((n & 0x0f0f) << 4);
9     n = ((n & 0xff00) >> 8) | ((n & 0x00ff) << 8);
10     n >> (16 - length)
11 }
12 
13 #[cfg(test)]
14 mod test {
15     use super::reverse_bits;
16     #[test]
test_bit_reverse()17     fn test_bit_reverse() {
18         assert_eq!(reverse_bits(0b0111_0100, 8), 0b0010_1110);
19         assert_eq!(
20             reverse_bits(0b1100_1100_1100_1100, 16),
21             0b0011_0011_0011_0011
22         );
23         // Check that we ignore >16 length
24         // We no longer check for this.
25         // assert_eq!(reverse_bits(0b11001100_11001100, 32), 0b0011001100110011);
26     }
27 }
28