Browsing by Subject "Burrows-Wheeler Transform"

The traditional way of computing the Burrows-Wheeler transform (BWT) has been to first build a suffix array, and then use this newly formed array to obtain the BWT. While this approach runs in linear time, the space requirement is far from optimal. When the length of the input string increases, the required working space quickly becomes too large for normal computers to handle. To overcome this issue, researchers have proposed many different types of algorithms for building the BWT. In 2009, Daisuke Okanohara and Kunihiko Sadakane presented a new linear time algorithm for BWT construction. This algorithm is relatively fast and requires far less working space than the traditional way of computing the BWT. It is based on a technique called induced sorting and can be seen as a state-of-the-art approach for internal memory BWT construction. However, a proper exploration of how to implement the algorithm efficiently has not been undertaken. One 32-bit implementation of the algorithm is known to exist, but due to the limitations of 32-bit programs, it can only be used for input strings under the size of 4 GB. This thesis introduces the algorithm from Okanohara and Sadakane and implements a 64-bit version of it. The implemented algorithm can in theory support input strings that are thousands of gigabytes in size. In addition to the explanation of the algorithm, the time and space requirements of the 64-bit implementation are compared to some other fast BWT algorithms.