Re: RISC-V Vector Task Group: fractional LMUL
David Horner
I left the encoding unspecified in the proposal. That was intentional as I saw various tradeoffs. However, I now recommend the codes be in order of increasing VLMAX value as so:
This allows for a quick "andi and bz"
check of the "special" LMUL 1/16
It also allows the formula
new LMUL = ( new sew / old SEW
) * old LMUL
to be implemented as
vlmul = new vsew - old vsew + old
vlmul
The first column could be inverted to
allow the original code values with no appreciable hardware cost,
but it complicates software for the two above cases.
On 2020-02-09 12:44 a.m., David Horner
via Lists.Riscv.Org wrote:
Special lmul code in vsetvl{i} to derive LML from existing SEW/LMUL and provided sew code.
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