code: function bnToBuffer(trimOrSize) {
      var res = new Buffer(this.toByteArray());
      if (trimOrSize === true && res[0] === 0) {
          res = res.slice(1);
      } else if (_.isNumber(trimOrSize)) {
          if (res.length > trimOrSize) {
              for (var i = 0; i < res.length - trimOrSize; i++) {
                  if (res[i] !== 0) {
                      return null;
                  }
              }
              return res.slice(res.length - trimOrSize);
          } else if (res.length < trimOrSize) {
              var padded = new Buffer(trimOrSize);
              padded.fill(0, 0, trimOrSize - res.length);
              res.copy(padded, trimOrSize - res.length);
              return padded;
          }
      }
      return res;
  }
docs: return Buffer object
  @param trim {boolean} slice buffer if first element == 0
  @returns {Buffer}