A system for translating compressed instructions to instructions in an executable format is described. A translation unit is configured to decompress compressed instructions into a native instruction format using X and Y indices accessed from a memory, a translation memory, and a program specified mix mask. A level 1 cache is configured to store the native instruction format for each compressed instruction. The memory may be configured as a paged instruction cache to store pages of compressed instructions intermixed with pages of uncompressed instructions. Methods of determining a mix mask for efficiently translating compressed instructions is also described. A genetic method uses pairs of mix masks as genes from a seed population of mix masks that are bred and may be mutated to produce pairs of offspring mix masks to update the seed population. A mix mask for efficiently translating compressed instructions is determined from the updated seed population.