Linux, 64-bit, Intel Core i5 2500:

-> unpatched:

$ ./python -m timeit -s 'import codecs; d = codecs.utf_16_be_decode; x = (" " * 1000).encode("utf-16be")' 'd(x)'
100000 loops, best of 3: 2.99 usec per loop

-> Victor's commit:

$ ./python -m timeit -s 'import codecs; d = codecs.utf_16_be_decode; x = (" " * 1000).encode("utf-16be")' 'd(x)'
100000 loops, best of 3: 2.83 usec per loop

-> utf16_decoder_shift_3.patch:

$ ./python -m timeit -s 'import codecs; d = codecs.utf_16_be_decode; x = (" " * 1000).encode("utf-16be")' 'd(x)'
1000000 loops, best of 3: 1.88 usec per loop


It seems that the wrong patch was committed.