binary_to_integer/1

z.erl

-module(z).
-compile(export_all).

pow(0, 0)  -> 0;
pow(0, _N) -> 1;
pow(K, N)  -> N * pow(K-1, N).

binary_to_integer(B) when is_binary(B) ->
    {_, N} = binary_to_integer1(B),
    N.

binary_to_integer_naive(B) ->
    list_to_integer(binary_to_list(B)).

binary_to_integer1(<<>>)                     -> {0, 0};
binary_to_integer1(<<D:1/binary, R/binary>>) ->
    case D of
	<<S>> when S == $- ->
	    {P, N} = binary_to_integer1(R),
	    {P, N * -1};
	<<C>> when C >= $0 andalso C =< $9 ->
	    {P, N} = binary_to_integer1(R),
	    {P+1, N + (C - $0) * pow(P, 10)}
    end.

test() ->
    N = <<"1234567890">>,
    M = z,
    {X, _N} = timer:tc(M, binary_to_integer_naive, [N]),
    {Y, _N} = timer:tc(M, binary_to_integer, [N]),
    {X, Y}.