density

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This simple encoder/decoder for https://github.com/jbenet/multihash/ works based on #1:

    // Test vector: "0x11","0x14","0x0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33"
    function encode(uint hashtype, uint size, bytes digest) returns (bytes hash) {
        hash = new bytes(2 + digest.length);

        hash = copyBytes(digest, 0, digest.length, hash, 0);

        hash[0] = bytes1(hashtype & 0xff);
        hash[1] = bytes1(size & 0xff);
    }

    // Test vector: "0x11140beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33"
    function decode(bytes hash) returns (uint hashtype, uint size, bytes digest) {
        uint len = hash.length;

        if (len < 3) {
            // invalid
            hashtype = 0;
            return;
        }

        hashtype = uint(hash[0]);
        size = uint(hash[1]);

        // extract the digest
        digest = copyBytes(hash, 2, size, 0);
    }