Quadratic Equation solver in dc (reverse polish calculator)

quadratic.dc

# Usage: dc < quadratic.dc
# Shortened to: dc -e '1 3 _4 2kscsbsa[X=]sf[lb2^4lalc**-v]sdlb_1*ldx-2la*/lfPplb_1*ldx+2la*/lfPp'

# Solves:
# x^2 + 3x – 4 = 0

1                              # A
3                              # B
_4                             # C

# set precision
2k

# Store c, b, and a
sc
sb
sa

# For 'X=' in our output
[X=]sf

# Define our equation solver for sqrt(b^2 - 4ac) so we can -b +/- <solution> / 2a
[
  lb 2 ^                       # b2
  4 la lc ** -                 # - 4ac
  v                            # square root of the above
]sd

# Figure first X
lb _1 * ldx -                  # -b - sqrt(b2-4ac)
2 la */                        # divided by 2a
lfP p                          # print 'X=<answer>'

# Figure second X
lb _1 * ldx +                  # -b + sqrt(b2-4ac)
2 la */                        # divided by 2a
lfP p                          # print 'X=<answer>'