needs lib/type num/math
unit hal/muldiv

: (one? ( op -- ?op f ) dup (i? if 1 = if drop 1 exit then then 0 ;
: ?shiftable ( op -- op f )
  dup (i? if ?dup if log2mod swap if drop else ( op n )
    i) swap (R> R>) 1 exit then then then 0 ;
: mulorshift, ( op -- ) (one? not if ?shiftable if <<, else *, then then ;
: divorshift, ( op -- ) (one? not if ?shiftable if >>, else /mod, then then ;
: ?modmask ( op -- op f )
  dup (i? if ?dup if dup pow2? not if drop else ( op n )
    1- i) swap (R> R>) 1 exit then then then 0 ;
: modorand, ( op -- )
  ?modmask if &, else
    dup /mod, dup (R> REGS = if drop else ( op )
      dup (dir? if S>) !, else (R> S) &) swap R>) @, then then then ;

: [*n] ( n -- n ) n< i) mulorshift, ; immediate
: [*n+] ( idx a -- a ) PSP) S>) @+, n< i) S>) mulorshift, S) &) +, ; immediate