Internal
one of "tooShort" (4 elements), "tooLong" (6 elements),
"identity" (flag=−2), "fullMatrix" (flag=−1), "diagOne" (flag=0), "offDiagOne" (flag=1)
spec.type — "float64array" for drotm's derived param64 spec
typed array of length 5 with the appropriate flag and coefficients
Builds a typed array for a named srotm/drotm
paramscenario.typeselects Float32Array (srotm, the default) or Float64Array (drotm, viaderive64's "param64" — seetypedArrayCtor).