Many versions of the fast Fourier transform require a reordering of ei
ther the input or the output data that corresponds to reversing the or
der of the bits in the array index. There has been a surprisingly larg
e number of papers on this subject in the recent literature. This pape
r collects 30 methods for bit reversing an array. Each method was reco
ded into a uniform style in Fortran and its performance measured on se
veral different machines, each with a different memory system. This pa
per includes a description of how the memories of the machines operate
to motivate two new algorithms that perform substantially better than
the others.