ENHANCED: library(crypto): Faster conversion to bytes when the integer is known.

These entailed constraints only affect performance, and can be removed
without affecting the correctness of the code. They speed up scalar
multiplication of a curve point, used for example in Bitcoinolog.

diff --git a/src/lib/crypto.pl b/src/lib/crypto.pl
index 42ce8f5d79f47c42208779c9823ec068f06c00e8..458283b751798967c66bbc356d511a582ddbc224 100644 (file)
--- a/src/lib/crypto.pl
+++ b/src/lib/crypto.pl
@@ -713,12 +713,17 @@ curve25519_scalar_mult(Scalar, Point, Result) :-
         '$curve25519_scalar_mult'(ScalarBytes, PointBytes, Result).
 
 bytes_integer(Bs, N) :-
-        foldl(pow, Bs, 0-0, N-_).
+        foldl(pow, Bs, t(0,0,N), t(N,_,_)).
 
-pow(B, N0-I0, N-I) :-
+pow(B, t(N0,P0,I0), t(N,P,I)) :-
+        (   integer(I0) ->
+            B #= I0 mod 256,
+            I #= I0 >> 8
+        ;   true
+        ),
         B in 0..255,
-        N #= N0 + B*256^I0,
-        I #= I0 + 1.
+        N #= N0 + B*256^P0,
+        P #= P0 + 1.
 
 /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    Operations on Elliptic Curves