Re: [Qemu-devel] [RFC] alpha qemu arithmetic exceptions

[Peter Maydell]

On 3 July 2014 23:47, Al Viro <address@hidden> wrote:
> How can that be correct?  Suppose a = b = 0.  We get
> tcg_gen_eqv_i64(tmp, va, vb);   ->      tmp = -1
> tcg_gen_mov_i64(tmp2, va);      ->      tmp2 = 0
> tcg_gen_add_i64(vc, va, vb);    ->      c = 0
> tcg_gen_xor_i64(tmp2, tmp2, vc);->      tmp2 = 0
> tcg_gen_and_i64(tmp, tmp, tmp2);->      tmp = -1

tmp2 here is 0, so the result of this AND is 0, not -1...

> tcg_gen_shri_i64(tmp, tmp, 63); ->      tmp = 1

so tmp = 0

> tcg_gen_movi_i64(tmp2, 0);      ->      tmp2 = 0
> gen_helper_check_overflow(cpu_env, tmp, tmp2);  -> not equal, overflow.

and tmp == tmp2, no overflow.

thanks
-- PMM