Quick hack / performance experiment to measure JavaScript variable byte encoding speed

variableByteEncoding.js

// Quick hack / performance experiment to measure JavaScript variable byte encoding speed
function encodeFloat(i) {
  var buf = [];
  buf.push(i & 127);
  i /= 128;
  while(i >= 1) {
    --i;
    buf.push(128 + (i & 127));
    i /= 128
  }
  return buf.reverse();
}
function decodeFloat(buf) {
  var pos = 0;
  var i = 0;
  var b;
  while(true) {
    b = buf[pos++];
    i = i * 128 + (b & 127);
    if(b & 128) {
      ++i;
    } else {
      return i;
    }
  }
}

function encodeInt(i) {
  var buf = [];
  buf.push(i & 127);
  i >>= 7;
  while(i >= 1) {
    --i;
    buf.push(128 + (i & 127));
    i >>= 7;
  }
  return buf.reverse();
}
function decodeInt(buf) {
  var pos = 0;
  var i = 0;
  var b;
  while(true) {
    b = buf[pos++] | 0;
    i = (i << 7)+ (b & 127);
    if(b & 128) {
      ++i;
    } else {
      return i;
    }
  }
}
function encodeFloatArr(i, buf, pos0) {
  var pos = pos0;
  buf[pos] = i & 127;
  i /= 128;
  while(i >= 1) {
    --i;
    buf[++pos] = 128 + (i & 127);
    i /= 128;
  }
  while(pos0 < pos) {
    i = buf[pos];
    buf[pos] = buf[pos0];
    buf[pos0] = i;
    ++pos0; --pos;
  }
  return buf;
}
function encodeIntArr(i, buf, pos0) {
  var pos = pos0;
  buf[pos] = i & 127;
  i >>= 7;
  while(i >= 1) {
    --i;
    buf[++pos] = 128 + (i & 127);
    i >>= 7;
  }
  while(pos0 < pos) {
    i = buf[pos];
    buf[pos] = buf[pos0];
    buf[pos0] = i;
    ++pos0; --pos;
  }
  return buf;
}

/*
bench("Float arr", encodeFloat, decodeFloat);
bench("Int arr", encodeInt, decodeInt);
bench("Float arr", encodeFloatArr, decodeFloat);
*/
bench("Int arr", encodeIntArr, decodeInt);

function bench(title, enc, dec) {
  var buf = new Uint8Array(30);
  // find total length, and warm up jit.
  var benchCount = 50000000;
  var totalLength = 0;
  for(var i=0;i<benchCount;++i) {
    var encoded = enc(i, buf, 0);
    totalLength += encoded.length;
    dec(encoded, buf, 0);
    if(dec(encoded, buf, 0) !== i) {
      console.log("error", i, encoded, dec(encoded, buf, 0));
    };
  }
  var t0 = Date.now();
  for(i=0;i<benchCount;++i) {
    dec(enc(i, buf, 0), buf, 0);
  }
  console.log(title, "KB/second", totalLength/1000/(Date.now() - t0));
}