%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2005-2013. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%
%%
%%% Description: SSH math utilities
-module(ssh_math).
-export([ipow/3]).
-export([ilog2/1, invert/2, ipow2/3]).
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% INTEGER utils
%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% calculate A^B mod M
ipow(A, B, M) when M > 0, B >= 0 ->
crypto:mod_exp(A, B, M).
ilog2(N) ->
ssh_bits:isize(N) - 1.
ipow2(A, B, M) when M > 0, B >= 0 ->
if A == 1 ->
1;
true ->
ipow2(A, B, M, 1)
end.
ipow2(A, 1, M, Prod) ->
(A*Prod) rem M;
ipow2(_A, 0, _M, Prod) ->
Prod;
ipow2(A, B, M, Prod) ->
B1 = B bsr 1,
A1 = (A*A) rem M,
if B - B1 == B1 ->
ipow2(A1, B1, M, Prod);
true ->
ipow2(A1, B1, M, (A*Prod) rem M)
end.
invert(X,P) when X > 0, P > 0, X < P ->
I = inv(X,P,1,0),
if
I < 0 -> P + I;
true -> I
end.
inv(0,_,_,Q) -> Q;
inv(X,P,R1,Q1) ->
D = P div X,
inv(P rem X, X, Q1 - D*R1, R1).
