test.html

<script>
    function readSize(rlp, idx, len) {
        var res = 0;
        for (var i = 0; i < len; i++) res += 256*res + rlp[idx+i];
        return res;
    }

    // length in bytes of the RLP element starting at position idx
    function rlpByteLength(rlp, idx) {
        var elem = rlp[idx];
        if (elem < 128) return [1, 0];
        if (elem == 128) return [0, 1];
        if (elem >= 247) {
            return [readSize(rlp, idx+1, elem-247), elem-247+1];
        }
        if (elem >= 192) {
            return [elem - 192, 1];
        }
        if (elem >= 183) {
            return [readSize(rlp, idx+1, elem-183), elem-183+1];
        }
        return [elem - 128, 1];
    }

    // length in bytes of the RLP element starting at position idx
    function rlpByteSkipLength(rlp, idx) {
        var elem = rlp[idx];
        if (elem < 128) return 1;
        if (elem == 128) return 1;
        if (elem >= 247) {
            return (readSize(rlp, idx+1, elem-247) + elem-247+1);
        }
        if (elem >= 192) {
            return (elem - 192 + 1);
        }
        if (elem >= 183) {
            return (readSize(rlp, idx+1, elem-183) + elem-183+1);
        }
        return (elem - 128 + 1);
    }

    // how many elements in an RLP array
    function rlpArrayLength(rlp, idx) {
        var len;
        var szlen;
        len = rlpByteLength(rlp, idx)[0];
        szlen = rlpByteLength(rlp, idx)[1];
        if (len == 0) return 0;
        var jdx = idx+szlen;
        var res = 0;
        while (jdx < len+idx+szlen) {
            var skip = rlpByteSkipLength(rlp, jdx);
            jdx += skip;
            res++;
        }
        return res;
    }
    
    var arr = [248,58,128,128,128,128,201,132,32,101,115,116,131,111,110,101,128,128,128,128,128,128,160,215,241,119,216,15,196,250,166,128,234,164,249,61,9,52,3,50,34,230,108,4,218,137,251,144,190,7,194,224,245,110,190,128,128,128,128,128]
    var arr1 = [226,23,160,134,97,180,49,195,176,247,20,246,126,221,205,132,143,63,142,131,107,6,212,128,198,157,102,114,191,216,23,170,17,185,136]
</script>