%%HP:T(3);
@ DEC2FRAC, by Joseph K. Horn
\<< DUP2 @ Must be two arguments.  Exit now if max denominator < 2,
  IF 1 > SWAP FP AND @ or if decimal fraction is an integer.
  THEN \-> f c @ Store decimal fraction, and max denominator.

    \<< 0 1 f @ Calculate only denominators.  Do numerator only at end.
      WHILE OVER c < OVER AND @ Do until bigger than max denominator
      REPEAT INV DUP FP 4 ROLLD IP OVER * ROT + ROT @ This is the
      END DROP DUP2 c @ recursion formula continued fraction expansion.

      IF DUP2 > @ Is there a possible "missing" fraction?
      THEN - OVER / CEIL * - @ This is the new, fast "jump backwards".
      ELSE 3 DROPN @ (Sometimes there's no need to jump.)
      END DUP2 1 2 @ Take the new denominator & the previous one, and

      START DUP f * 0 RND SWAP / f - ABS SWAP @ turn into fractions.
      NEXT @ See which one's closest to the original decimal fraction.

      IF > @ Compare the two solutions, and
      THEN SWAP @ pick the better one.
      END DROP DUP f * 0 RND SWAP @ Calculate the numerator.
    \>> @ End of real work; now clean up the output.

    IF DUP ABS 1 > @ Is the denominator greater than 1?
    THEN -3 CF # 5603Eh SYSEVAL @ If so, make output into 'A/B' form.
    ELSE DROP @ Otherwise, get rid of extraneous denominator,
    END @ and exit program.

  ELSE DROP @ If bad arguments, do nothing to "decimal fraction", but
  END @ get rid of "maximum denominator" and exit program.
\>>