X-Git-Url: http://git.ozlabs.org/?p=ccan;a=blobdiff_plain;f=ccan%2Fcrypto%2Fshachain%2Fshachain.c;h=9cb54a37bdd9da6c18b1567e400ca132010af9a2;hp=4b6a31db3f93f419282ead63467495999263fd54;hb=e6abb93d50ba9f1e90163d7db53be70b8ef81a96;hpb=fc6655ed3c4840a5d4d669ad3c44e2ffe1019173

diff --git a/ccan/crypto/shachain/shachain.c b/ccan/crypto/shachain/shachain.c
index 4b6a31db..9cb54a37 100644
--- a/ccan/crypto/shachain/shachain.c
+++ b/ccan/crypto/shachain/shachain.c
@@ -10,77 +10,116 @@ static void change_bit(unsigned char *arr, size_t index)
 	arr[index / CHAR_BIT] ^= (1 << (index % CHAR_BIT));
 }
 
-static void derive(shachain_index_t index, size_t bits, struct sha256 *hash)
+static unsigned int count_trailing_zeroes(uint64_t index)
 {
+#if HAVE_BUILTIN_CTZLL
+	return index ? (unsigned int)__builtin_ctzll(index) : SHACHAIN_BITS;
+#else
+	unsigned int i;
+
+	for (i = 0; i < SHACHAIN_BITS; i++) {
+		if (index & (1ULL << i))
+			break;
+	}
+	return i;
+#endif
+}
+
+static bool can_derive(uint64_t from, uint64_t to)
+{
+	uint64_t mask;
+
+	/* Corner case: can always derive from seed. */
+	if (from == 0)
+		return true;
+
+	/* Leading bits must be the same */
+	mask = ~(((uint64_t)1 << count_trailing_zeroes(from))-1);
+	return ((from ^ to) & mask) == 0;
+}
+
+static void derive(uint64_t from, uint64_t to,
+		   const struct sha256 *from_hash,
+		   struct sha256 *hash)
+{
+	uint64_t branches;
 	int i;
 
-	for (i = bits - 1; i >= 0; i--) {
-		if (!((index >> i) & 1)) {
+	assert(can_derive(from, to));
+
+	/* We start with the first hash. */
+	*hash = *from_hash;
+
+	/* This represents the bits set in to, and not from. */
+	branches = from ^ to;
+	for (i = ilog64(branches) - 1; i >= 0; i--) {
+		if (((branches >> i) & 1)) {
 			change_bit(hash->u.u8, i);
-			sha256(hash, hash, 1);
+			sha256(hash, hash, sizeof(*hash));
 		}
 	}
 }
 
-void shachain_from_seed(const struct sha256 *seed, shachain_index_t index,
+void shachain_from_seed(const struct sha256 *seed, uint64_t index,
 			struct sha256 *hash)
 {
-	*hash = *seed;
-	derive(index, sizeof(index) * CHAR_BIT, hash);
+	derive(0, index, seed, hash);
 }
 
-void shachain_init(struct shachain *shachain)
+uint64_t shachain_next_index(const struct shachain *chain)
 {
-	shachain->num_valid = 0;
+	return chain->min_index - 1;
 }
 
-/* We can only ever *unset* bits, so to must only have bits in from. */
-static bool can_derive(shachain_index_t from, shachain_index_t to)
+void shachain_init(struct shachain *chain)
 {
-	return (~from & to) == 0;
+	chain->num_valid = 0;
+	/* This is 0 in the case where SHACHAIN_BITS is 64. */
+	chain->min_index = (UINT64_MAX >> (64 - SHACHAIN_BITS)) + 1;
 }
 
-void shachain_add_hash(struct shachain *chain,
-		       shachain_index_t index, const struct sha256 *hash)
+bool shachain_add_hash(struct shachain *chain,
+		       uint64_t index, const struct sha256 *hash)
 {
-	int i;
+	unsigned int i, pos;
 
-	for (i = 0; i < chain->num_valid; i++) {
-		/* If we could derive this value, we don't need it,
-		 * not any others (since they're in order). */
-		if (can_derive(index, chain->known[i].index))
-			break;
+	/* You have to insert them in order! */
+	assert(index == shachain_next_index(chain));
+
+	pos = count_trailing_zeroes(index);
+
+	/* All derivable answers must be valid. */
+	/* FIXME: Is it sufficient to check just the next answer? */
+	for (i = 0; i < pos; i++) {
+		struct sha256 expect;
+
+		/* Make sure the others derive as expected! */
+		derive(index, chain->known[i].index, hash, &expect);
+		if (memcmp(&expect, &chain->known[i].hash, sizeof(expect)))
+			return false;
 	}
 
-	/* This can happen if you skip indices! */
-	assert(i < sizeof(chain->known) / sizeof(chain->known[0]));
-	chain->known[i].index = index;
-	chain->known[i].hash = *hash;
-	chain->num_valid = i+1;
+	chain->known[pos].index = index;
+	chain->known[pos].hash = *hash;
+	if (pos + 1 > chain->num_valid)
+		chain->num_valid = pos + 1;
+	chain->min_index = index;
+	return true;
 }
 
 bool shachain_get_hash(const struct shachain *chain,
-		       shachain_index_t index, struct sha256 *hash)
+		       uint64_t index, struct sha256 *hash)
 {
-	int i;
+	unsigned int i;
 
 	for (i = 0; i < chain->num_valid; i++) {
-		shachain_index_t diff;
-
 		/* If we can get from key to index only by resetting bits,
 		 * we can derive from it => index has no bits key doesn't. */
 		if (!can_derive(chain->known[i].index, index))
 			continue;
 
-		/* Start from this hash. */
-		*hash = chain->known[i].hash;
-
-		/* This indicates the bits which are in 'index' and
-		 * not the key */
-		diff = index ^ chain->known[i].index;
-
-		/* Using ilog64 here is an optimization. */
-		derive(~diff, ilog64(diff), hash);
+		derive(chain->known[i].index, index, &chain->known[i].hash,
+		       hash);
 		return true;
 	}
 	return false;