From b566beaa387bd4e1dc9062dc92c3be7ea6db3917 Mon Sep 17 00:00:00 2001
From: Mirek Kratochvil <exa.exa@gmail.com>
Date: Sun, 2 Feb 2014 17:18:48 +0100
Subject: [PATCH] permutation: avoid needlessly precomputed hpermInv

---
 src/matrix.cpp    |  2 +-
 src/mce.cpp       | 15 ++++-----------
 src/permutation.h |  6 +++++-
 3 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/src/matrix.cpp b/src/matrix.cpp
index 751f0a5..9992330 100644
--- a/src/matrix.cpp
+++ b/src/matrix.cpp
@@ -174,7 +174,7 @@ void matrix::generate_random_with_inversion (uint size, matrix&inversion, prng&r
 	}
 	*this = lt;
 	this->mult (ut);
-	ut.compute_inversion (inversion,	true, false);
+	ut.compute_inversion (inversion, true, false);
 	lt.compute_inversion (ut, false, true);
 	inversion.mult (ut);
 }
diff --git a/src/mce.cpp b/src/mce.cpp
index 4eb710e..f41f282 100644
--- a/src/mce.cpp
+++ b/src/mce.cpp
@@ -42,14 +42,12 @@ int mce::generate (pubkey&pub, privkey&priv, prng&rng, uint m, uint t)
 	S.generate_random_with_inversion (generator.height(), priv.Sinv, rng);
 
 	//scramble permutation
-	permutation P;
-	P.generate_random (generator.width(), rng);
-	P.compute_inversion (priv.Pinv);
+	priv.Pinv.generate_random (generator.width(), rng);
 
 	//public key
 	pub.t = t;
 	S.mult (generator);
-	P.permute (S, pub.G);
+	priv.Pinv.permute_inv (S, pub.G);
 
 	return 0;
 }
@@ -96,11 +94,8 @@ int privkey::decrypt (const bvector&in, bvector&out, bvector&errors)
 	Pinv.permute (in, not_permuted);
 
 	//prepare for decoding
-	permutation hpermInv; //TODO pre-invert it in prepare()
-	hperm.compute_inversion (hpermInv);
-
 	bvector canonical, syndrome;
-	hpermInv.permute (not_permuted, canonical);
+	hperm.permute_inv (not_permuted, canonical);
 	h.mult_vec_right (canonical, syndrome);
 
 	//decode
@@ -140,7 +135,6 @@ int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prn
 	uint i, s, t;
 	bvector p, e, synd, synd_orig, e2;
 	std::vector<uint> epos;
-	permutation hpermInv;
 	polynomial loc, Synd;
 
 	s = hash_size();
@@ -149,8 +143,7 @@ int privkey::sign (const bvector&in, bvector&out, uint delta, uint attempts, prn
 
 	//first, prepare the codeword to canonical form for decoding
 	Pinv.permute (in, e2);
-	hperm.compute_inversion (hpermInv);
-	hpermInv.permute (e2, p);
+	hperm.permute_inv (e2, p);
 
 	//prepare extra error vector
 	e.resize (s, 0);
diff --git a/src/permutation.h b/src/permutation.h
index b3fc970..2908871 100644
--- a/src/permutation.h
+++ b/src/permutation.h
@@ -44,12 +44,16 @@ public:
 			item (i) = i;
 	}
 
-	//TODO permute_inv is easy, do it everywhere
 	template<class A, class R> void permute (const A&a, R&r) const {
 		r.resize (a.size() );
 		for (uint i = 0; i < size(); ++i) r[item (i) ] = a[i];
 	}
 
+	template<class A, class R> void permute_inv (const A&a, R&r) const {
+		r.resize (a.size() );
+		for (uint i = 0; i < size(); ++i) r[i] = a[item (i)];
+	}
+
 	void permute_rows (const matrix&, matrix&) const;
 
 	//work-alike for dyadic permutations.