AoC 2021 day 13, part 1 (dc)

#!/usr/bin/dc

# Process fold section (storing first fold axis and line in a and l)
[
    sl sa                       # store line, axis (clobber, only want first fold)
    d _1!=R                     # loop until top is -1
] sR
lRx s.

[ ll2* lx- sx ] sX              # macro to flip in x
[ ll2* ly- sy ] sY              # macro to flip in y

[ lY sF [ly] sA ] sS            # macro to swap x-macros for y-macros
[ lx ] sA                       # store axis value loader in A
lX sF                           # start with X in F (flip transform macro)
la 121=S                        # if doing Y, S will change the above macros

[ lc1- sc ] sM                  # point merged, reduce count

# Loop to transform each point and check for collisions
[
    sy sx                       # store point into x,y
    lAx ll<F                    # execute transform if on far side of line

    ly 10000* lx+               # calculate hash (10000y + x)
    d;h 1=M 1 r:h               # (h(hash) = 1, merge) (h(hash) = 1)

    z 0<L                       # loop while points on stack
] sL

z 2/ sc                         # init count with number of points (stack/2)
lLx                             # start loop

[Part 1: ]n lcp