docs/programming/reference/library/src/2p/gate/rub.md · urbit.org

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1### `++rub`

3Length-decode

5The inverse of `++mat`. Accepts a cell of index `a` and a bitstring `b`

6and produces the cell whose tail `q` is the decoded atom at index `a`

7and whose head is the length of the encoded atom `q`, by which the

8offset `a` is advanced. Only used internally as a helper cue.

10Accepts

11-------

13`a` is an atom.

15`b` is a bitstring as an atom.

17Produces

18--------

20A cell of two atoms, `p` and `q`.

22Source

23------

25 ++ rub :: length-decode

26 ~/ %rub

27 |= {a/@ b/@}

28 ^- {p/@ q/@}

29 =+ ^= c

30 =+ [c=0 m=(met 0 b)]

31 |- ?< (gth c m)

32 ?. =(0 (cut 0 [(add a c) 1] b))

33 c

34 $(c +(c))

35 ?: =(0 c)

36 [1 0]

37 =+ d=(add a +(c))

38 =+ e=(add (bex (dec c)) (cut 0 [d (dec c)] b))

39 [(add (add c c) e) (cut 0 [(add d (dec c)) e] b)]

42Examples

43--------

45 ~zod/try=> `@ub`(jam 0xaaa)

46 0b1.0101.0101.0101.0010.0000

47 ~zod/try=> (rub 1 0b1.0101.0101.0101.0010.0000)

48 [p=20 q=2.730]

49 ~zod/try=> `@ux`q:(rub 1 0b1.0101.0101.0101.0010.0000)

50 0xaaa

52***