From 7c3f359c9ce1b735f302a2579df2924bfc2f7ded Mon Sep 17 00:00:00 2001 From: Mirek Kratochvil Date: Tue, 25 Sep 2012 09:44:23 +0200 Subject: [PATCH] dyadic permutations --- include/codecrypt.h | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) diff --git a/include/codecrypt.h b/include/codecrypt.h index 37e1e46..15fa4f7 100644 --- a/include/codecrypt.h +++ b/include/codecrypt.h @@ -137,6 +137,39 @@ public: } void permute_rows (const matrix&, matrix&) const; + + //work-alike for dyadic permutations. + template static bool permute_dyadic + (uint sig, const V&a, V&r) { + + //check if the thing has size 2^n + uint s = a.size(); + while (s > 1) { + if (s & 1) return false; + s >>= 1; + } + + if (sig >= a.size() ) return false; + + r.resize (a.size() ); + + uint i, t, x; + for (i = 0; i < a.size(); ++i) { + r[sig] = a[i]; + + //flip the correct bit in signature + t = i + 1; + x = 1; + while (! (t & 1) ) { + t >>= 1; + x <<= 1; + } + sig ^= x; + } + + return true; + } + }; /*