benchmark/bm_so_mandelbrot.rb: add new benchmark

benchmark/bm_so_mandelbrot.rb

@@ -0,0 +1,57 @@
+#  The Computer Language Benchmarks Game
+#  http://shootout.alioth.debian.org/
+#
+#  contributed by Karl von Laudermann
+#  modified by Jeremy Echols
+
+size = 600 # ARGV[0].to_i
+
+puts "P4\n#{size} #{size}"
+
+ITER = 49                           # Iterations - 1 for easy for..in looping
+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.
+for y in 0..count_size
+  for x in 0..count_size
+    zr = 0.0
+    zi = 0.0
+    cr = (2.0*x/size)-1.5
+    ci = (2.0*y/size)-1.0
+    escape = false
+
+    # To make use of the for..in code, we use a dummy variable,
+    # like one would in C
+    for dummy in 0..ITER
+      tr = zr*zr - zi*zi + cr
+      ti = 2*zr*zi + ci
+      zr, zi = tr, ti
+
+      if (zr*zr+zi*zi) > LIMIT_SQUARED
+        escape = true
+        break
+      end
+    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)
+      print byte_acc.chr
+      byte_acc = 0
+      bit_num = 0
+    elsif (x == count_size)
+      byte_acc <<= (8 - bit_num)
+      print byte_acc.chr
+      byte_acc = 0
+      bit_num = 0
+    end
+  end
+end