On 11/04/19 11:06, David Laight wrote: > It may be possible to generate shorter code that executes just as > fast by generating a single constant and deriving the others from it. > - generate 4s - needed first > - shift right 2 to get 1s (in parallel with the xor) > - use lea to get 6s (in parallel with an lea to do the add) > - invert the 1s to get FEs (also in parallel with the add) > - xor the FEs with the 6s to get F8s (in parallel with the or) > - and/test for the result FWIW, here is yet another way to do it: /* Change 6/7 to 4/5 */ data &= ~((data & 0x0404040404040404ULL) >> 1); /* Only allow 0/1/4/5 now */ return !(data & 0xFAFAFAFAFAFAFAFAULL); movabs $0x404040404040404, %rcx andq %rdx, %rcx shrq %rcx notq %rcx movabs $0xFAFAFAFAFAFAFA, %rax andq %rcx, %rdx test %rax, %rdx Paolo
