AoC 2021, day 3 (dc part 2)

# Command:
#
# highbit = 2048
# dc -e`dc -e"$highbit sb" -e'2i' -finput -e"[1r-] sN" -fdc-p2.dc` \
#    -e`dc -e"$highbit sb" -e'2i' -finput -e"[] sN"    -fdc-p2.dc` \
#    -e'*p'
#
# Script takes two pieces of input code:
#     1) setting b to the high bit (2048 for the input or 16 for test)
#     2) an N macro to negate the logic for the Oxygen calculation
#

Ai                  # back to decimal

#2048sb              # for input (pass in this or 16sb for test case)

# Quit reducing: size setIndex
[
    *               # clear size=1
    1 r;Gx          # get first/only value in array[setIndex]
    lb lo *+ p      # apply remainder if needed and print exit
    q               # quit
] sq

# Macros so we can get and set to different arrays with
# value index array ;Sx  -> this does array[array][index] = value
# index array ;Gx        -> this returns array[array][index]
[:0] 0:S [:1] 1:S
[;0] 0:G [;1] 1:G

# Filter: i=size num1 num2 num3 ...
[
    0Sn                     # clear counts
    # num1 num2 num3 ...
    [
        lb                  # b num
        ~r                  # bit rest

        dd;n 1+ d_3Rr:n     # num[bit]++; num[bit] bit rest
        r;Sx                # array[bit][num] = rest; num2 ...

        z 0<L
    ] dsLx

    # 0s - 1s | +'ve  0   -'ve
    # --------+---------=--------
    # Oxygen  |  0    1    1
    # CO2     |  1    0    0
    #
    # So we want d.-1/ (1 if +'ve, 0 if 0 or -'ve), and to negate (1r-) for the Oxygen
    0;n 1;n- d.1-/ lNx      # do check to get index of target array
    dlo 2*+ so              # append that bit to the output

    d;n                     # i=size setIndex
    d1=q                    # stop if only one left

    # load passing values from successful array back onto stack
    [
        r d3R d3R           # set i i  set
        ;Gx                 # get( set[i] ) i set
        _3R 1- d0<I         # i-- set get(set[i])
    ] dsIx *+               # clear i=0 and set

    lb2/dsb 0<F             # shift highbit right, loop until we quit or run off end
] dsFx