[erlang-questions] Indexed element access: array vs. erlang:element

[Joel Reymont]

On Aug 25, 2008, at 3:56 PM, Dimitry Golubovsky wrote:

> Joel,
>
> If nobody did it before, then I'll do (not earlier than tonight  
> anyway ;)


Here, check out the performance of fixed-size vs extensible array set  
op.

Astounding!

---

Mac OSX Leopard 10.5.4

Mac Pro 2x2.8Ghz Quad-Core Intel Xeon, 14Gb 800Mhz DDR2 FB-DIMM

Erlang (BEAM) emulator version 5.6.3 [source] [64-bit] [smp:8] [async- 
threads:0] [kernel-poll:false]

%% 10K elements

14> arr:test().
Fixed-size array: get:     1256ns, set:     6667ns
Extensible array: get:     1255ns, set:       22ns
Tuple:            get:      659ns, set:        6ns
ok

%% 1 million

15> arr:test(1000000).
Fixed-size array: get:   121881ns, set:   777067ns
Extensible array: get:   120026ns, set:       35ns
Tuple:            get:    66288ns, set:       40ns
ok

---

-module(arr).

-compile([export_all]).

data1(N) ->
     %% size implies fixed-size array
     %% but lets be explicit
     array:new([{size, N}, {default, 0}, {fixed, true}]).

data2(N) ->
     %% extensible array
     array:new([{size, N}, {default, 0}, {fixed, false}]).

data3(N) ->
     erlang:make_tuple(N, 0).

array_set(Array, I, Value) ->
     %% array indexing starts at 0
     array:set(I - 1, Value, Array).

tuple_set(Tuple, I, Value) ->
     %% tuple indexing starts at 1
     setelement(I, Tuple, Value).

array_get(Array, I) ->
     array:get(I - 1, Array).

tuple_get(Tuple, I) ->
     element(I, Tuple).

get(_, _, 0) ->
     ok;

get(Fun, Data, N) ->
     Fun(Data, N),
     get(Fun, Data, N - 1).

set(_, _, 0) ->
     ok;

set(Fun, Data, N) ->
     Data1 = Fun(Data, N, N),
     set(Fun, Data1, N - 1).

test() ->
     test(10000).

test(N) ->
     %% fixed-size array
     {G1, _} = timer:tc(arr, get, [{arr, array_get}, data1(N), N]),
     {S1, _} = timer:tc(arr, set, [{arr, array_set}, data1(N), N]),
     %% extensible array
     {G2, _} = timer:tc(arr, get, [{arr, array_get}, data2(N), N]),
     {S2, _} = timer:tc(arr, set, [{arr, array_get}, data2(N), N]),
     %% tuple
     {G3, _} = timer:tc(arr, get, [{arr, tuple_get}, data3(N), N]),
     {S3, _} = timer:tc(arr, set, [{arr, tuple_get}, data3(N), N]),
     %% results
     io:format("Fixed-size array: get: ~8wns, set: ~8wns~n", [G1 , S1]),
     io:format("Extensible array: get: ~8wns, set: ~8wns~n", [G2 , S2]),
     io:format("Tuple:            get: ~8wns, set: ~8wns~n", [G3 , S3]),
     ok.



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