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