An efficient parallel Gibbs sampler using butterfly-patterned partial sums is provided. Instead of building and searching a complete prefix sums table, an alternative “butterfly patterned partial sums table” is described that integrates a lightweight transposition and partial sums operation. Accordingly, the usual full matrix transposition and full prefix sums table building operations can be omitted in favor of building the butterfly-patterned partial sums table, which requires less computational and communication effort. This butterfly-patterned partial sums table is used by a modified binary search phase that calculates the needed prefix-sum table values on-the-fly using the butterfly-patterned partial sums table. Transposed memory access is also provided while avoiding the full matrix transform, providing significant performance benefits for highly parallel architectures, such as graphics processing units (GPUs) where 1-stride or sequential memory accesses are important for optimization.