bm_so_mandelbrot.rb

#  The Computer Language Benchmarks Game
#  http://shootout.alioth.debian.org/
#
#  contributed by Karl von Laudermann
#  modified by Jeremy Echols
#  modified by Detlef Reichl

#size = ARGV[0].to_i

size = 256

puts "P4\n#{size} #{size}"

ITER = 50                           # Iterations
LIMIT_SQUARED = 4.0                 # Presquared limit

byte_acc = 0
bit_num = 0

count_size = size - 1               # Precomputed size for easy for..in looping

# For..in loops are faster than .upto, .downto, .times, etc.
# That's not true, but left it here
for y in 0..count_size
  for x in 0..count_size
    zr = 0.0
    zi = 0.0
    cr = (2.0*x.to_f/size.to_f)-1.5
    ci = (2.0*y.to_f/size.to_f)-1.0
    escape = false

    zrzr = zr*zr
    zizi = zi*zi
    ITER.times do
      tr = zrzr - zizi + cr
      ti = 2.0*zr*zi + ci
      zr = tr
      zi = ti
      # preserve recalculation
      zrzr = zr*zr
      zizi = zi*zi
      if zrzr+zizi > LIMIT_SQUARED
        escape = true
        break
      end
#      nil
    end

    byte_acc = (byte_acc << 1) | (escape ? 0b0 : 0b1)
    bit_num += 1

    # Code is very similar for these cases, but using separate blocks
    # ensures we skip the shifting when it's unnecessary, which is most cases.
    if (bit_num == 8)
      printf "%c", byte_acc # .chr
      byte_acc = 0
      bit_num = 0
    elsif (x == count_size)
      byte_acc <<= (8 - bit_num)
      printf "%c", byte_acc # .chr
      byte_acc = 0
      bit_num = 0
    else
      0
    end
 #   nil
  end
end