On Mon, Feb 24, 2025 at 01:55:28PM -0800, H. Peter Anvin wrote: > On 2/24/25 07:24, Uros Bizjak wrote: > > > > > > On 23. 02. 25 17:42, Kuan-Wei Chiu wrote: > > > Refactor parity calculations to use the standard parity8() helper. This > > > change eliminates redundant implementations and improves code > > > efficiency. > > > > The patch improves parity assembly code in bootflag.o from: > > > > 58: 89 de mov %ebx,%esi > > 5a: b9 08 00 00 00 mov $0x8,%ecx > > 5f: 31 d2 xor %edx,%edx > > 61: 89 f0 mov %esi,%eax > > 63: 89 d7 mov %edx,%edi > > 65: 40 d0 ee shr %sil > > 68: 83 e0 01 and $0x1,%eax > > 6b: 31 c2 xor %eax,%edx > > 6d: 83 e9 01 sub $0x1,%ecx > > 70: 75 ef jne 61 <sbf_init+0x51> > > 72: 39 c7 cmp %eax,%edi > > 74: 74 7f je f5 <sbf_init+0xe5> > > 76: > > > > to: > > > > 54: 89 d8 mov %ebx,%eax > > 56: ba 96 69 00 00 mov $0x6996,%edx > > 5b: c0 e8 04 shr $0x4,%al > > 5e: 31 d8 xor %ebx,%eax > > 60: 83 e0 0f and $0xf,%eax > > 63: 0f a3 c2 bt %eax,%edx > > 66: 73 64 jae cc <sbf_init+0xbc> > > 68: > > > > which is faster and smaller (-10 bytes) code. > > > > Of course, on x86, parity8() and parity16() can be implemented very simply: > > (Also, the parity functions really ought to return bool, and be flagged > __attribute_const__.) There was a discussion regarding return type when parity8() was added. The integer type was taken over bool with a sort of consideration that bool should be returned as an answer to some question, like parity_odd(). To me it's not a big deal. We can switch to boolean and describe in comment what the 'true' means for the parity() function.
