Expand description
Generic runtime-dispatch register-blocked sub-matrix GEMV (y += A · x,
row stride lda).
Generalizes super::gemv() to a row-major sub-matrix: nrows × ncols
with leading dimension lda ≥ ncols (rows contiguous over ncols, spaced
lda apart). lda = ncols recovers the packed gemv. This admits matvec
over a trailing/leading block of a larger buffer — e.g. the column-major
trailing block of a reflector apply, whose columns are contiguous but spaced
by the buffer’s row count — without copying the block out. Result
accumulates into y.