\ dmath.fs -- double-precision math
\ doubles are stored on stack as two integers, n1 n2
\ d = n1 + 4294967296 * n2
\ Multiplication
: d* ( d1 d2 -- d1*d2 )
\ (n1 + c * n2)(n3 + c * n4)
\ n1*n3 + c*(n2*n3 + n1*n4) + c^2*n2*n4