On 09/01/2015 11:27, Frediano Ziglio wrote:
>
> Signed-off-by: Frediano Ziglio <frediano.zig...@huawei.com>
> ---
> include/qemu-common.h | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/include/qemu-common.h b/include/qemu-common.h
> index f862214..5366220 100644
> --- a/include/qemu-common.h
> +++ b/include/qemu-common.h
> @@ -370,6 +370,7 @@ static inline uint8_t from_bcd(uint8_t val)
> }
>
> /* compute with 96 bit intermediate result: (a*b)/c */
> +#ifndef __x86_64__
> static inline uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c)
> {
> union {
> @@ -392,6 +393,18 @@ static inline uint64_t muldiv64(uint64_t a, uint32_t b,
> uint32_t c)
> res.l.low = (((rh % c) << 32) + (rl & 0xffffffff)) / c;
> return res.ll;
> }
> +#else
> +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;
> +}
> +#endif
>
Good idea. However, if you have __int128, you can just do
return (__int128)a * b / c
and the compiler should generate the right code. Conveniently, there is
already CONFIG_INT128 that you can use.
Paolo
