On Thursday 17 December 2015 15:10:12 Andrey Semashev wrote: > On 2015-12-17 14:50, Andrey Semashev wrote: > >On 2015-12-17 02:44, Kamil Rytarowski wrote: > >> > >>On 16.12.2015 11:02, Pali Rohár wrote: > >>> > >>>Hi! There is probably no portable way for checking CPU type. But > >>>you do not need to know CPU type here. You need to know if CPU has > >>>fast 64bit numeric operations (and use 64bit speed optimization), > >>>right? > >>> > >>>And this could be possible by checking size of int_fast32_t type > >>>(defined in stdint.h). If is same as size of int_fast64_t type then > >>>you could use 64bit optimization otherwise not (= 32bit integers > >>>are faster then 64bit). > >>> > >>>But I will let this suggestion for reviewing of other people. > >> > >>This sounds like a good way to go. > > > >I don't think it does. int_fast32_t does not have to be 64-bit if 32-bit > >integers are fast. Yes. I did not wrote that int_fast32_t must be 64-bit. I wrote to compare size of int_fast32_t and int_fast64_t. > >It _may_ be larger than 32-bit if 32-bit integers are > >slow (most likely - do not have the target hardware support). I don't > >think this is the case for x32 or x86_64. On 64bi x86 sizeof(int_fast32_t) is 8 and sizeof(int_fast64_t) also 8. On 32bit x86 sizeof(int_fast32_t) is only 4. > >If integer performance is what this preprocessor check influences, I'd > >suggest checking the size of size_t. Or testing for particular > >architectures explicitly, with 64-bit being the default and 32-bit only > >for the tested architectures (this would probably make the code more > >easily maintainable in the future). > > I've sent this privately in error. > > Also, it seems size_t is 32-bit on x32, so disregard that suggestion. Important question is: what you want to distinguish? It is not 32 vs 64 bit processor right? It is if architecture has 64bit long registers? Or something else? -- Pali Rohár pali.rohar at gmail.com
