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Date: Fri, 16 Aug 2002 00:50:04 +0200
From: Richard Nyberg <rnyberg@it.su.se>
To: caml-list@inria.fr
Subject: [Caml-list] Bigarray access speed
Message-ID: <20020815225004.GA5959@gromit.it.su.se>
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In the following small programs 3) is faster than 1) and 2), which run
equally fast. However, 4 is significantly slower than the rest. If you
change the line "a.{i} <- a.{i} + i" to "a.{i} <- i" the execution time
is halfed but it's still much slower.

Are access to Bigarrays slower when passed to functions? If so, is it
fixable? or is there some workaround?

I stumbled upon this while coding on a school assignment ((not too ;) fast
multiplication of large integers).

1)
let a = Array.make 1000000 0 in
for i = 0 to 999999 do
    a.(i) <- a.(i) + i;
done;;

2)
let a = Array.make 1000000 0 in
let rec loop a i =
  if i <= 999999 then begin
    a.(i) <- a.(i) + i;
    loop a (i + 1)
  end in
loop a 0;;

3)
open Bigarray;;
let a = Array1.create int c_layout 1000000 in
Array1.fill a 0;
for i = 0 to 999999 do
  a.{i} <- a.{i} + i
done;;

4)
open Bigarray;;
let a = Array1.create int c_layout 1000000 in
Array1.fill a 0;
let rec loop a i =
  if i <= 999999 then begin
    a.{i} <- a.{i} + i;
    loop a (i + 1)
  end in
loop a 0;;

	-Richard
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