FDOT (2-way, multiple and indexed vector, FP8 to FP16)

Multi-vector 8-bit floating-point dot-product by indexed element to half-precision

The instruction computes the fused sum-of-products of a group of two 8-bit floating-point values held in the corresponding 16-bit elements of the two or four first source vectors and the indexed 16-bit element of the second source vector. The half-precision sum-of-products are scaled by 2^{-UInt(FPMR.LSCALE[3:0])}, before being destructively added without intermediate rounding to the corresponding half-precision elements of the ZA single-vector groups. The 8-bit floating-point encoding format for the elements of the first source vector and the second source vector is selected by FPMR.F8S1 and FPMR.F8S2 respectively.

The 8-bit floating-point pairs within the second source vector are specified using an immediate index which selects the same pair position within each 128-bit vector segment.

The vector numbers forming the single-vector group within each half of or each quarter of the ZA array are selected by the sum of the vector select register and immediate offset, modulo half or quarter the number of ZA array vectors. The vector group symbol, VGx2 or VGx4, indicates that the ZA operand consists of two or four ZA single-vector groups respectively. The vector group symbol is preferred for disassembly, but optional in assembler source code.

This instruction is unpredicated.

It has encodings from 2 classes: Two ZA single-vectors and Four ZA single-vectors

Two ZA single-vectors
(FEAT_SME_F8F16)

if !IsFeatureImplemented(FEAT_SME_F8F16) then UNDEFINED; integer v = UInt('010':Rv); integer n = UInt(Zn:'0'); integer m = UInt('0':Zm); integer offset = UInt(off3); integer index = UInt(i3h:i3l); constant integer nreg = 2;

Four ZA single-vectors
(FEAT_SME_F8F16)

if !IsFeatureImplemented(FEAT_SME_F8F16) then UNDEFINED; integer v = UInt('010':Rv); integer n = UInt(Zn:'00'); integer m = UInt('0':Zm); integer offset = UInt(off3); integer index = UInt(i3h:i3l); constant integer nreg = 4;