Re: [Qemu-devel] [PATCH 2/9] tcg: Add INDEX_op_extract2_{i32,i64}

[Richard Henderson]

On 3/26/19 8:35 PM, Peter Maydell wrote:
> On Thu, 7 Mar 2019 at 14:47, Richard Henderson
> <address@hidden> wrote:
>>
>> This will let backends implement the double-word shift operation.
>>
>> Signed-off-by: Richard Henderson <address@hidden>
>> diff --git a/tcg/README b/tcg/README
>> index 603f4df659..ddabf33017 100644
>> --- a/tcg/README
>> +++ b/tcg/README
>> @@ -343,6 +343,11 @@ at bit 8.  This operation would be equivalent to
>>
>>  (using an arithmetic right shift).
>>
>> +* extract2_i64 dest, t1, t2, pos
>> +
>> +Extract a 64-bit quantity from the concatenation of t2:t1,
>> +beginning at pos.
>> +
> 
> I think we should document the valid values of 'pos'.
> My guess is "0 <= pos <= 63".

How about

----
* extract2_i32/i64 dest, t1, t2, pos

For N = {32,64}, extract an N-bit quantity from the concatenation
of t2:t1, beginning at pos.  The tcg_gen_extract2_* expander allows
values 0 <= pos <= N, but will expand 0 and N with mov, so only
1 <= pos <= N-1 will be seen by the host tcg_out_op.
----

?


r~