On February 24, 2025 2:17:29 PM PST, Yury Norov <yury.norov@xxxxxxxxx> wrote: >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. Bool is really the single-bit type, and gives the compiler more information. You could argue that the function really should be called parity_odd*() in general, but that's kind of excessive IMO.
