--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/templates5/bfc.scala Thu Dec 06 18:37:17 2018 +0000
@@ -0,0 +1,179 @@
+// Part 2 about a "Compiler" for the Brainf*** language
+//======================================================
+
+// !!! Copy any function you need from file bf.scala !!!
+//
+// If you need any auxiliary function, feel free to
+// implement it, but do not make any changes to the
+// templates below.
+
+def time_needed[T](n: Int, code: => T) = {
+ val start = System.nanoTime()
+ for (i <- 0 until n) code
+ val end = System.nanoTime()
+ (end - start)/(n * 1.0e9)
+}
+
+type Mem = Map[Int, Int]
+
+import io.Source
+import scala.util._
+
+// !! COPY from your bf.scala !!
+
+// def load_bff(name: String) : String = ...
+
+// def sread(mem: Mem, mp: Int) : Int = ...
+
+// def write(mem: Mem, mp: Int, v: Int) : Mem = ...
+
+// def jumpRight(prog: String, pc: Int, level: Int) : Int = ...
+
+// def jumpLeft(prog: String, pc: Int, level: Int) : Int = ...
+
+// def compute(prog: String, pc: Int, mp: Int, mem: Mem) : Mem = ...
+
+// def run(prog: String, m: Mem = Map()) =
+
+// The baseline to what we can compare our "compiler"
+// implemented below. It should require something like
+// 60 seconds for the calculation on my laptop
+//
+//time_needed(1, run(load_bff("benchmark.bf")))
+
+
+// DEBUGGING INFORMATION!!!
+//
+// Compiler, even real ones, are fiendishly difficult to get
+// to produce correct code. The point is that for example for
+// the Sierpinski program, they need to still generate code
+// that displays such a triangle. If yes, then one usually
+// can take comfort that all is well. If not, then something
+// went wrong during the optimisations.
+
+
+// ADVANCED TASKS
+//================
+
+// (5) Write a function jtable that precomputes the "jump
+// table" for a bf-program. This function takes a bf-program
+// as an argument and Returns a Map[Int, Int]. The
+// purpose of this map is to record the information
+// that given on the position pc is a '[' or a ']',
+// then to which pc-position do we need to jump next?
+//
+// For example for the program
+//
+// "+++++[->++++++++++<]>--<+++[->>++++++++++<<]>>++<<----------[+>.>.<+<]"
+//
+// we obtain the map
+//
+// Map(69 -> 61, 5 -> 20, 60 -> 70, 27 -> 44, 43 -> 28, 19 -> 6)
+//
+// This states that for the '[' on position 5, we need to
+// jump to position 20, which is just after the corresponding ']'.
+// Similarly, for the ']' on position 19, we need to jump to
+// position 6, which is just after the '[' on position 5, and so
+// on. The idea is to not calculate this information each time
+// we hit a bracket, but just look up this information in the
+// jtable. You can use the jumpLeft and jumpRight functions
+// from Part 1 for calculating the jtable.
+//
+// Then adapt the compute and run functions from Part 1 in order
+// to take advantage of the information stored in the jtable.
+// This means whenever jumpLeft and jumpRight was called previously,
+// you should look up the jump address in the jtable.
+
+
+//def jtable(pg: String) : Map[Int, Int] = ...
+
+// testcase
+// jtable("""+++++[->++++++++++<]>--<+++[->>++++++++++<<]>>++<<----------[+>.>.<+<]""")
+// => Map(69 -> 61, 5 -> 20, 60 -> 70, 27 -> 44, 43 -> 28, 19 -> 6)
+
+
+//def compute2(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = ...
+
+//def run2(pg: String, m: Mem = Map()) = ...
+
+
+//testcase
+//time_needed(1, run2(load_bff("benchmark.bf")))
+
+
+
+// (6) Write a function optimise which deletes "dead code" (everything
+// that is not a bf-command) and also replaces substrings of the form
+// [-] by a new command 0. The idea is that the loop [-] just resets the
+// memory at the current location to 0. In the compute3 and run3 functions
+// below you implement this command by writing the number 0 to mem(mp),
+// that is write(mem, mp, 0).
+//
+// The easiest way to modify a string in this way is to use the regular
+// expression """[^<>+-.,\[\]]""", which recognises everything that is
+// not a bf-command and replace it by the empty string. Similarly the
+// regular expression """\[-\]""" finds all occurrences of [-] and
+// by using the Scala method .replaceAll you can replace it with the
+// string "0" standing for the new bf-command.
+
+//def optimise(s: String) : String = ...
+
+//def compute3(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = ...
+
+//def run3(pg: String, m: Mem = Map()) = ...
+
+
+// testcases
+
+//optimise(load_bff("benchmark.bf")) // should have inserted 0's
+//optimise(load_bff("mandelbrot.bf")).length // => 11203
+
+//time_needed(1, run3(load_bff("benchmark.bf")))
+
+
+
+// (7) Write a function combine which replaces sequences
+// of repeated increment and decrement commands by appropriate
+// two-character commands. For example for sequences of +
+//
+// orig bf-cmds | replacement
+// ------------------------------
+// + | +A
+// ++ | +B
+// +++ | +C
+// |
+// ... |
+// |
+// +++....+++ | +Z
+// (where length = 26)
+//
+// Similar for the bf-command -, > and <. All other commands should
+// be unaffected by this change.
+//
+// Adapt the compute4 and run4 functions such that they can deal
+// appropriately with such two-character commands.
+
+
+//def combine(s: String) : String = ...
+
+
+// testcase
+//combine(load_bff("benchmark.bf"))
+
+//def compute4(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = ...
+
+// should call first optimise and then combine on the input string
+//def run4(pg: String, m: Mem = Map()) = ...
+
+
+// testcases
+//combine(optimise(load_bff("benchmark.bf"))) // => """>A+B[<A+M>A-A]<A[[....."""
+
+//time_needed(1, run4(load_bff("benchmark.bf")))
+
+//time_needed(1, run(load_bff("sierpinski.bf")))
+//time_needed(1, run4(load_bff("sierpinski.bf")))
+
+//time_needed(1, run4(load_bff("mandelbrot.bf")))
+
+