unit num/math

: pow2 ( n -- n ) 1 swap lshift ;
code pow2? S) &) !, 1 i) -, S) &) &, 0 i) =) bool, exit,

: log2mod ( n -- mod n )
  ?dup not ?abort"log2 can't compute 0"
  dup 0 begin ( orig n i ) swap 2/ ?dup while swap 1+ repeat ( orig i )
  tuck pow2 - swap ;
: log2 ( n -- n ) log2mod nip ;
: log2# ( n -- n ) log2mod swap if abort"not a power of 2" then ;

: roundup ( n div -- n ) tuck /+ * ;
: rounddown ( n div -- n ) tuck / * ;

\ Heron's method
: isqrt ( n -- n )
  dup 1 <= if exit then
  r! 2/ begin dup r@ over / + 2/ ( hi lo )
  2dup > while nip repeat rdrop drop ;

code abs ( n -- n ) 0 i) signed) <) if, 0 i) swap-, then exit,