Re: [PULL 06/15] target/s390x: vxeh2: vector string search

[Richard Henderson]

On 5/13/22 08:54, Peter Maydell wrote:
> > +    s390_vec_write_element64(v1, 0, k << es);
>
> Specifically here, because k is 32 bit but s390_vec_write_element64()
> takes a uint64_t argument, we will do the shift as a signed 32 bit
> value before widening to 64 bits, so if the values of 'k' and 'es'
> are such that we might shift beyond bit 32 we'll get the wrong
> value. It looks like 'es' is one of the MO_* values, so generally
> small, but the upper bound on 'k' is a bit less obvious to me.
> Is the overflow-of-32-bits case impossible?

No, the upper bound of (k << es) is 16.

We perform the operation with k in units of element size, so that indexing works nicely, 
then convert back to units of bytes at the end to report results.  It's a byte index into 
the vector register, with 16 as an indicator of match not found + eos not found.


r~