On 9 January 2015 at 11:25, Frediano Ziglio <fredd...@gmail.com> wrote: > As this platform can do multiply/divide using 128 bit precision use > these instructions to implement it. > > Signed-off-by: Frediano Ziglio <frediano.zig...@huawei.com> > --- > include/qemu-common.h | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/include/qemu-common.h b/include/qemu-common.h > index f3033ae..880659d 100644 > --- a/include/qemu-common.h > +++ b/include/qemu-common.h > @@ -370,11 +370,23 @@ static inline uint8_t from_bcd(uint8_t val) > } > > /* 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 */
This assumption isn't necessarily true, and this implementation will dump core on overflow. For instance: Inputs: a = 8000000000000000 b = 80000000 c = 1 fn muldiv64 result 0 fn muldiv64_with_int128 result 0 fn muldiv64_with_uint128 result 0 Floating point exception (core dumped) -- PMM