// Part 2 about a "Compiler" for the Brainf*** language
//======================================================
object M5b {
// !!! 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._
def load_bff(name: String) : String =
Try(Source.fromFile(name)("ISO-8859-1").mkString).getOrElse("")
def sread(mem: Mem, mp: Int) : Int =
mem.getOrElse(mp, 0)
def write(mem: Mem, mp: Int, v: Int) : Mem =
mem.updated(mp, v)
def jumpRight(prog: String, pc: Int, level: Int) : Int = {
if (prog.length <= pc) pc
else (prog(pc), level) match {
case (']', 0) => pc + 1
case (']', l) => jumpRight(prog, pc + 1, l - 1)
case ('[', l) => jumpRight(prog, pc + 1, l + 1)
case (_, l) => jumpRight(prog, pc + 1, l)
}
}
def jumpLeft(prog: String, pc: Int, level: Int) : Int = {
if (pc < 0) pc
else (prog(pc), level) match {
case ('[', 0) => pc + 1
case ('[', l) => jumpLeft(prog, pc - 1, l - 1)
case (']', l) => jumpLeft(prog, pc - 1, l + 1)
case (_, l) => jumpLeft(prog, pc - 1, l)
}
}
def compute(prog: String, pc: Int, mp: Int, mem: Mem) : Mem = {
if (0 <= pc && pc < prog.length) {
val (new_pc, new_mp, new_mem) = prog(pc) match {
case '>' => (pc + 1, mp + 1, mem)
case '<' => (pc + 1, mp - 1, mem)
case '+' => (pc + 1, mp, write(mem, mp, sread(mem, mp) + 1))
case '-' => (pc + 1, mp, write(mem, mp, sread(mem, mp) - 1))
case '.' => { print(sread(mem, mp).toChar); (pc + 1, mp, mem) }
case '[' =>
if (sread(mem, mp) == 0) (jumpRight(prog, pc + 1, 0), mp, mem) else (pc + 1, mp, mem)
case ']' =>
if (sread(mem, mp) != 0) (jumpLeft(prog, pc - 1, 0), mp, mem) else (pc + 1, mp, mem)
case _ => (pc + 1, mp, mem)
}
compute(prog, new_pc, new_mp, new_mem)
}
else mem
}
def run(prog: String, m: Mem = Map()) = compute(prog, 0, 0, m)
// 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 fiedishly difficult to get
// to prduce 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.
// (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] =
(0 until pg.length).collect { pc => pg(pc) match {
case '[' => (pc -> jumpRight(pg, pc + 1, 0))
case ']' => (pc -> jumpLeft(pg, pc - 1, 0))
}}.toMap
// 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 = {
if (0 <= pc && pc < pg.length) {
val (new_pc, new_mp, new_mem) = pg(pc) match {
case '>' => (pc + 1, mp + 1, mem)
case '<' => (pc + 1, mp - 1, mem)
case '+' => (pc + 1, mp, write(mem, mp, sread(mem, mp) + 1))
case '-' => (pc + 1, mp, write(mem, mp, sread(mem, mp) - 1))
case '.' => { print(sread(mem, mp).toChar); (pc + 1, mp, mem) }
case '[' =>
if (sread(mem, mp) == 0) (tb(pc), mp, mem) else (pc + 1, mp, mem)
case ']' =>
if (sread(mem, mp) != 0) (tb(pc), mp, mem) else (pc + 1, mp, mem)
case _ => (pc + 1, mp, mem)
}
compute2(pg, tb, new_pc, new_mp, new_mem)
}
else mem
}
def run2(pg: String, m: Mem = Map()) =
compute2(pg, jtable(pg), 0, 0, m)
//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 occurences of [-] and
// by using the Scala method .replaceAll you can repplace it with the
// string "0" standing for the new bf-command.
def optimise(s: String) : String = {
s.replaceAll("""[^<>+-.\[\]]""","")
.replaceAll("""\[-\]""", "0")
}
def compute3(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = {
if (0 <= pc && pc < pg.length) {
val (new_pc, new_mp, new_mem) = pg(pc) match {
case '0' => (pc + 1, mp, write(mem, mp, 0))
case '>' => (pc + 1, mp + 1, mem)
case '<' => (pc + 1, mp - 1, mem)
case '+' => (pc + 1, mp, write(mem, mp, sread(mem, mp) + 1))
case '-' => (pc + 1, mp, write(mem, mp, sread(mem, mp) - 1))
case '.' => { print(sread(mem, mp).toChar); (pc + 1, mp, mem) }
case '[' =>
if (sread(mem, mp) == 0) (tb(pc), mp, mem) else (pc + 1, mp, mem)
case ']' =>
if (sread(mem, mp) != 0) (tb(pc), mp, mem) else (pc + 1, mp, mem)
case _ => (pc + 1, mp, mem)
}
compute3(pg, tb, new_pc, new_mp, new_mem)
}
else mem
}
def run3(pg: String, m: Mem = Map()) = {
val pg_opt = optimise(pg)
compute3(pg_opt, jtable(pg_opt), 0, 0, m)
}
// testcases
//println(optimise(load_bff("collatz.bf")))
//optimise(load_bff("benchmark.bf")) // should have inserted 0's
//optimise(load_bff("mandelbrot.bf")).length // => 11205
//time_needed(1, run3(load_bff("benchmark.bf")))
//time_needed(1, run3(load_bff("mandelbrot.bf")))
// (7) Write a function combine which replaces sequences
// of repated 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 splice(cs: List[Char], acc: List[(Char, Int)]) : List[(Char, Int)] = (cs, acc) match {
case (Nil, acc) => acc
case ('[' :: cs, acc) => splice(cs, ('[', 1) :: acc)
case (']' :: cs, acc) => splice(cs, (']', 1) :: acc)
case ('.' :: cs, acc) => splice(cs, ('.', 1) :: acc)
case ('0' :: cs, acc) => splice(cs, ('0', 1) :: acc)
case (c :: cs, Nil) => splice(cs, List((c, 1)))
case (c :: cs, (d, n) :: acc) =>
if (c == d && n < 26) splice(cs, (c, n + 1) :: acc)
else splice(cs, (c, 1) :: (d, n) :: acc)
}
def spl(s: String) = splice(s.toList, Nil).reverse
//spl(load_bff("benchmark.bf"))
def combine(s: String) : String = {
(for ((c, n) <- spl(s)) yield c match {
case '>' => List('>', (n + '@').toChar)
case '<' => List('<', (n + '@').toChar)
case '+' => List('+', (n + '@').toChar)
case '-' => List('-', (n + '@').toChar)
case _ => List(c)
}).flatten.mkString
}
//combine(load_bff("benchmark.bf"))
def compute4(pg: String, tb: Map[Int, Int], pc: Int, mp: Int, mem: Mem) : Mem = {
if (0 <= pc && pc < pg.length) {
val (new_pc, new_mp, new_mem) = pg(pc) match {
case '0' => (pc + 1, mp, write(mem, mp, 0))
case '>' => (pc + 2, mp + (pg(pc + 1) - '@'), mem)
case '<' => (pc + 2, mp - (pg(pc + 1) - '@'), mem)
case '+' => (pc + 2, mp, write(mem, mp, sread(mem, mp) + (pg(pc + 1) - '@')))
case '-' => (pc + 2, mp, write(mem, mp, sread(mem, mp) - (pg(pc + 1) - '@')))
case '.' => { print(sread(mem, mp).toChar); (pc + 1, mp, mem) }
case '[' =>
if (sread(mem, mp) == 0) (tb(pc), mp, mem) else (pc + 1, mp, mem)
case ']' =>
if (sread(mem, mp) != 0) (tb(pc), mp, mem) else (pc + 1, mp, mem)
case _ => (pc + 1, mp, mem)
}
compute4(pg, tb, new_pc, new_mp, new_mem)
}
else mem
}
def run4(pg: String, m: Mem = Map()) = {
val pg_opt = combine(optimise(pg))
compute4(pg_opt, jtable(pg_opt), 0, 0, m)
}
// testcases
//println(combine(optimise(load_bff("mandelbrot.bf").drop(123))))
//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")))
//println(time_needed(1, run4(load_bff("mandelbrot.bf"))))
}
/*
import CW10b._
println(time_needed(1, run(load_bff("collatz.bf"))))
println(time_needed(1, run2(load_bff("collatz.bf"))))
println(time_needed(1, run3(load_bff("collatz.bf"))))
println(time_needed(1, run4(load_bff("collatz.bf"))))
*/