2015-01-09 11:43 GMT+00:00 Paolo Bonzini <pbonz...@redhat.com>: > > > On 09/01/2015 12:25, Frediano Ziglio wrote: >> /* compute with 96 bit intermediate result: (a*b)/c */ >> -#ifdef CONFIG_INT128 >> +#if defined(CONFIG_INT128) && !defined(__x86_64__) >> static inline uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c) >> { >> return (__int128)a * b / c; >> } >> +#elif defined(__x86_64__) >> +/* Optimised x64 version. This assume that a*b/c fits in 64 bit */ >> +static inline uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c) >> +{ >> + uint64_t res; >> + >> + asm ("mulq %2\n\tdivq %3" >> + : "=a"(res) >> + : "a"(a), "qm"((uint64_t) b), "qm"((uint64_t)c) >> + : "rdx", "cc"); >> + return res; >> +} > > Reorder it the other way, and you can simplify the first #if. >
Yes, I was however thinking about people reading code. The int128 version is much easier to read so I put it first. > I applied patch 1 locally, and will send a pull request once the tree is > thawed. > > Paolo Frediano