On 7/24/2024 3:03 AM, Robin Dapp wrote:
Thanks for the explanation! I have a few clarification questions about this.
If I understand correctly, B would represent the number of elements the
vector can have (for 128b vector operating on 32b elements, B == 4, but if
operating on 64b elements B == 2); however, I'm not too sure what A
represents.
The runtime size of a vector is a polynomial with a "base size" of A and
"increments beyond A" of B. B is compile-time variable/indeterminate and
runtime invariant. For (non-zve32) RVV it specifies the number of 64-bit
chunks beyond the minimum size of 64 bits. The polynomial is [2 2] in that
case and the "vector bit size" would be
64 * [2 2] = [128 128] = 128 + x * 128.
For a runtime vector size of 256 bits, x would be 1 and so on and we determine
it at runtime via csrr.
On the poly_int docs, it says
An indeterminate value of 0 should usually represent the minimum possible
runtime value, with c0 specifying the value in that case.
"minimum possible runtime value" doesn't make sense to me. Does it mean the
potential minimum bound of elements it will operate on?
This refers to the minimum runtime size of a vector, the constant 2 * 64 bit
above. So it doesn't talk about the number of elements. The number of
elements can be deducted from the "vector size" polynomial by dividing it by
the element size. The minimum number of elements for an element size S could
e.g. be [128 128] / S = 128 / S + x * (128 / S).
I think all of this makes sense to me! Thanks for all the explanations!
Edwin
