obsolete: see 293169

bignum_sqrt.erl

%% square root function for integers in Erlang
%% by Kenji Rikitake <kenji.rikitake@acm.org> 26-JAN-2010
%% Distributed under MIT license at the end of the source code.

-module(bignum_sqrt).

-export([sqrt/1]).

%% significand digits for float estimation
-define(DIGITS, 10).

%% computing square root of N
%% with Newton-Raphson method

sqrt(N) when (is_integer(N) and (N > 0)) ->
    % estimation of the root by the float calc
    L = integer_to_list(N),
    Len = length(L),
    case Len > ?DIGITS of
	true ->
	    Exp = Len - ?DIGITS,
	    M = list_to_integer(lists:sublist(L, ?DIGITS)),
	    XM = math:exp(math:log(M) / 2) * 
		 math:pow(10, (Exp rem 2) / 2),
	    X = list_to_integer(integer_to_list(trunc(XM)) ++ 
				lists:duplicate(Exp div 2, $0));
	false ->
	    X = trunc(math:sqrt(N))
    end,
    sqrt(N, X).

sqrt(N, X) ->
    % Newton-Raphson method of solving square root
    X2 = ((N div X) + X) div 2,
    case X2 =/= X of
	true ->
	    sqrt(N, X2);
	false ->
	    X
    end.

%%  MIT License:
%%  Copyright (c) 2010 by Kenji Rikitake.
%%
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%%  copies of the Software, and to permit persons to whom the
%%  Software is furnished to do so, subject to the following
%%  conditions:
%%
%%  The above copyright notice and this permission notice shall be
%%  included in all copies or substantial portions of the Software.
%%
%%  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
%%  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
%%  OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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%%  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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