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) -> u163pub 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