[Shootout-list] OCaml compilation flags, improved Mandelbrot

[Christian Szegedy]

I have experienced dramatic speedup of the harmonic.ocaml, when
compiled with the  command

ocamlop -unsafe -inline 100

The shootout page compiles the code without "-inline 100" which
produces much worse code on my box.

I coud also improve the speed of the Mandelbrot computation.
The following code is about 10-20% faster on my box than
the one in the shootout:



let niter = 50
let limit = 2.

let limit2 = limit *. limit

type complex = {mutable r:float;mutable i:float}

exception Found of int

let add_bit0 tmp c byte =
  tmp.r <- c.r;
  tmp.i <- c.i;
  try
     for i = 1 to niter do
        if tmp.r *. tmp.r +. tmp.i *. tmp.i > 4.0 then
          raise ( Found ((byte lsl 1) lor 0x00));
        let m = 2. *. tmp.r *. tmp.i +. c.i in
        tmp.r <- tmp.r *. tmp.r -. tmp.i *. tmp.i +. c.r;
        tmp.i <- m;
     done;
     (byte lsl 1) lor 0x01
  with
     Found i -> i

let () =
  let w = int_of_string Sys.argv.(1) in
  let h = w in
  let fw = float w
  and fh = float h
  and cplmt8 = 8 - w mod 8 in
  Printf.printf "P4\n%i %i\n" w h;
  let byte = ref 0
  and bit = ref 0 in
  let c   = {r=0.0;i=0.0} in
  let tmp = {r=0.0;i=0.0} in
  for y = 0 to h - 1 do
    c.i <- 2. *. float y /. fh -. 1.;
    for x = 0 to w - 1 do
        c.r <- 2. *. float x /. fw -. 1.5;
      byte := add_bit0 tmp c !byte;
      incr bit;
      if !bit = 8 then (
          output_byte stdout !byte;
          byte := 0;
          bit := 0;
       )
    done;
    if !bit <> 0 then (
      output_byte stdout (!byte lsl cplmt8);
      byte := 0;
      bit := 0;
     )
  done