> In order to port VMS to new architectures, DEC/HP/VSI ... 

> turned the VAX MACRO assembly language (in which 

> some of the VMS operating system was written) into a
> portable implementation language by 'compiling' the 

> high-level CISC VAX instructions (and addressing modes) 

> into sequences of RISC instructions. 

Clem Pease did the same thing to port TMG from IBM 7000-series machines to the GE  600 series for Multics, circa 1967. Although both architectures had 36-bit words, it was a challenge to adequately emulate IBM's accumulator, which supported 38-bit sign-magnitude addition, 37-bit twos-complement and 36-bit ones-complement.

Doug