# Crate bit_reverse [−] [src]

## Library Objective

This library provides a number of ways to compute the bit reversal of all primitive integers. There are currently 3 different algorithms implemented: Bitwise, Parallel, and Lookup reversal.

## Example

use bit_reverse::ParallelReverse; assert_eq!(0xA0u8.swap_bits(), 0x05u8);

This library is very simple to uses just import the crate and the algorithm you want to use.
Then you can call `swap_bits`

() on any primitive integer. If you want to try a different
algorithm just change the use statement and now your program will use the algorithm instead.

## YMMV Performance Comparison

I wouldn't use `BitwiseReverse`

as it is mainly there for completeness and is strictly inferior
to `ParallelReverse`

, which is a Bitwise Parallel Reverse and thus an order of magnitude faster.
For small sizes, <= 16 bits, `LookupReverse`

is the fastest but it doesn't scale as well as
`ParallelReverse`

this is because `ParallelReverse`

does a constant number of operations for
every size (assuming your cpu has a hardware byte swap instruction). `LookupReverse`

needs more
lookups, ANDs, and ORs for each size increase. Thus `ParallelReverse`

performs a little better
at 32 bits and much better at 64 bits. These runtime characteristics are based on a Intel(R)
Core(TM) i7-4770K CPU @ 3.50GHz.

## Memory Consumption

`BitwiseReverse`

and `ParallelReverse`

both only use a couple of stack variables for their
computations. `LookupReverse`

on the other hand statically allocates 256 u8s or 256 bytes to
do its computations. `LookupReverse`

's memory cost is shared by all of the types
'LookupReverse` supports.

## no_std Compatible

To link to core instead of STD, disable default features for this library in your Cargo.toml. Cargo choosing features

## Traits

BitwiseReverse |
Computes bit reversal by going bit by bit and setting the reverse position bit for the output. |

LookupReverse |
Computes bit reversal by using lookup table to translate a single byte into its reverse. For multi-byte types, the byte order is swapped to complete the reversal. |

ParallelReverse |
Computes bit reversal by using a divide and conquer approach. Pairs of bits are swapped. Then neighboring bit pairs are swapped. Each time swapping the next largest group of bits. This is done until the entire data has been bit reversed. |