bsearch.erl

-module(bsearch).
-export([find/2]).

find(List, Value_to_find) ->
	Max = lists:max(List),
	Min = lists:nth(1, List),
	
	case Value_to_find of
		_ when Value_to_find > Max -> {error, toobig};
		_ when Value_to_find < Min -> {error, toosmall};
		_ -> {ok, find(List, Value_to_find, 0)}
	end.
	
find(List, Value_to_find, Offset) ->
	End_i = length(List),
	Mid_i = floor(End_i/2),
	Mid_e = lists:nth(Mid_i, List),

	case Mid_e of
		_ when Value_to_find > Mid_e ->
			{_, Last} = lists:split(Mid_i, List),
			find(Last, Value_to_find, (Offset + Mid_i));
		_ when Value_to_find < Mid_e ->
			{First, _} = lists:split(Mid_i, List),
			find(First, Value_to_find, Offset);
		_ -> (Mid_i + Offset)
	end.
	
floor(X) ->
    T = erlang:trunc(X),
    case (X - T) of
        Neg when Neg < 0 -> T - 1;
        Pos when Pos > 0 -> T;
        _ -> T
    end.