BME280 module refactor

The BME280 module is a bit unnecessarily large, so I'm refactoring it, primarily to remove unnecessary variable declarations and debugging code, reduce the length of non-minifiable public method names and generally tidy up a bit.

Is there a protocol for this sort of thing, eg discussing here, or should I just change and create a pull request?

FWIW here's the code, anything else?

/* Copyright (c) 2015 Masafumi Okada. See the file LICENSE for copying permission. */
/*
Read Temperature, Pressure, and Humidity from Bosch Sensortec's BME280 sensor module.
*/

var C = {ADDR: 0x76}

function BME280(_i2c) {
  var t = this;
  t.i2c = _i2c;

  var osrs_t = 1;  //Temperature oversampling x 1
  var osrs_p = 1;  //Pressure oversampling x 1
  var osrs_h = 1;  //Humidity oversampling x 1
  var mode = 3;    //Normal mode
  var t_sb = 5;    //Tstandby 1000ms
  var filter = 0;  //Filter off
  var spi3w_en = 0;//3-wire SPI Disable

  var ctrl_meas_reg = (osrs_t << 5) | (osrs_p << 2) | mode;
  var config_reg = (t_sb << 5) | (filter << 2) | spi3w_en;
  var ctrl_hum_reg = osrs_h;

  t.wReg(0xF2, ctrl_hum_reg);
  t.wReg(0xF4, ctrl_meas_reg);
  t.wReg(0xF5, config_reg);

  t.rCoeffs();
}

/* Concatinate two Uint8Arrays */
BME280.prototype.concatU8 = function(a, b) {
  var c = new Uint8Array(a.length + b.length);
  c.set(a);
  c.set(b, a.length);
  return (c);
};

/* Convert two UInt8 value into one "signed" number */
BME280.prototype.convS16 = function(ub1, ub2) {
  var value = (ub1 << 8) + ub2;
  if (value & 0x8000) {
    value = -((value - 1) ^ 0xffff);
  }
  return (value);
};

/* Write single byte to register reg_address */
BME280.prototype.wReg = function(reg_address, data) {
  this.i2c.writeTo(C.ADDR, [reg_address, data]);
};

/* Read single byte from register reg*/
BME280.prototype.read8 = function(reg) {
  this.i2c.writeTo(C.ADDR, reg);
  return this.i2c.readFrom(C.ADDR, 1)[0];
};

/* Read and store all coefficients stored in the sensor */
BME280.prototype.rCoeffs = function() {
  var t = this, i = t.i2c;
  i.writeTo(C.ADDR, 0x88);
  var data = i.readFrom(C.ADDR, 24);
  i.writeTo(C.ADDR, 0xA1);
  data = t.concatU8(data, i.readFrom(C.ADDR, 1));
  i.writeTo(C.ADDR, 0xE1);
  data = t.concatU8(data, i.readFrom(C.ADDR, 7));

  t.T1 = (data[1] << 8) | data[0];
  t.T2 = t.convS16(data[3], data[2]);
  t.T3 = t.convS16(data[5], data[4]);

  t.P1 = (data[7] << 8) | data[6];
  t.P2 = t.convS16(data[9], data[8]);
  t.P3 = t.convS16(data[11], data[10]);
  t.P4 = t.convS16(data[13], data[12]);
  t.P5 = t.convS16(data[15], data[14]);
  t.P6 = t.convS16(data[17], data[16]);
  t.P7 = t.convS16(data[19], data[18]);
  t.P8 = t.convS16(data[21], data[20]);
  t.P9 = t.convS16(data[23], data[22]);
  t.H1 = data[24];
  t.H2 = t.convS16(data[26], data[25]);
  t.H3 = data[27];
  t.H4 = (data[28] << 4) | (0x0F & data[29]);
  t.H5 = (data[30] << 4) | ((data[29] >> 4) & 0x0F); 
  t.H6 = data[31]; 

};

/* Read Raw data from the sensor */
BME280.prototype.rdRaw = function() {
  var t = this;
  t.i2c.writeTo(C.ADDR, 0xF7);
  var data = t.i2c.readFrom(C.ADDR, 8);
  t.pres_raw = (data[0] << 12) | (data[1] << 4) | (data[2] >> 4);
  t.temp_raw = (data[3] << 12) | (data[4] << 4) | (data[5] >> 4);
  t.hum_raw = (data[6] << 8) | data[7];
};

/* Calibration of Temperature, algorithm is taken from the datasheet */
BME280.prototype.cal_T = function(adc_T) {
  var t = this, 
      v1 = ((adc_T) / 16384.0 - (t.T1) / 1024.0) * (t.T2),
      v2 = (((adc_T) / 131072.0 - (t.T1) / 8192.0) * ((adc_T) / 131072.0 - (t.T1) / 8192.0)) * (t.T3);
  t.t_fine = (v1 + v2);
  return 100 * t.t_fine / 5120.0;
};

/* Calibration of Pressure, algorithm is taken from the datasheet */
BME280.prototype.cal_P = function(adc_P) {
  var v2, p, t = this, v1 = (t.t_fine / 2.0) - 64000.0;  
  v2 = v1 * v1 * (t.P6) / 32768.0;
  v2 = v2 + v1 * (t.P5) * 2.0;
  v2 = (v2 / 4.0) + ((t.P4) * 65536.0);
  v1 = ((t.P3) * v1 * v1 / 524288.0 + (t.P2) * v1) / 524288.0;
  v1 = (1.0 + v1 / 32768.0) * (t.P1);
  if (v1 === 0.0) {
    return 0; // avoid exception caused by division by zero
  }
  p = 1048576.0 - adc_P;
  p = (p - (v2 / 4096.0)) * 6250.0 / v1;
  v1 = (t.P9) * p * p / 2147483648.0;
  v2 = p * (t.P8) / 32768.0;
  p = p + (v1 + v2 + (t.P7)) / 16.0;
  return p;
};

/* Calibration of Humidity, algorithm is taken from the datasheet */
BME280.prototype.cal_H = function(adc_H) {
  var t = this, v1 = (t.t_fine - (76800));
  v1 = (((((adc_H << 14) - ((t.H4) << 20) - ((t.H5) * v1)) +
    (16384)) >> 15) * (((((((v1 * (t.H6)) >> 10) *
      (((v1 * (t.H3)) >> 11) + (32768))) >> 10) + (2097152)) *
    (t.H2) + 8192) >> 14));
  v1 = (v1 - (((((v1 >> 15) * (v1 >> 15)) >> 7) * (t.H1)) >> 4));
  v1 = (v1 < 0 ? 0 : v1);
  v1 = (v1 > 419430400 ? 419430400 : v1);
  return (v1 >> 12);
};

exports.connect = function(_i2c) {
  return (new BME280(_i2c));
};