AVR Freaks

https://github.com/milesburton/Arduino-Temperature-Control-Library/blob/master/DallasTemperature.cpp#L249

does:

void DallasTemperature::setResolution(uint8_t newResolution) {

	bitResolution = constrain(newResolution, 9, 12);
	DeviceAddress deviceAddress;
	for (int i = 0; i < devices; i++) {
		getAddress(deviceAddress, i);
		setResolution(deviceAddress, bitResolution, true);
	}

}

The implementation of setResolution() immediately follows:

bool DallasTemperature::setResolution(const uint8_t* deviceAddress,
		uint8_t newResolution, bool skipGlobalBitResolutionCalculation) {

	// ensure same behavior as setResolution(uint8_t newResolution)
	newResolution = constrain(newResolution, 9, 12);

	// return when stored value == new value
	if (getResolution(deviceAddress) == newResolution)
		return true;

	ScratchPad scratchPad;
	if (isConnected(deviceAddress, scratchPad)) {

		// DS1820 and DS18S20 have no resolution configuration register
		if (deviceAddress[0] != DS18S20MODEL) {

			switch (newResolution) {
			case 12:
				scratchPad[CONFIGURATION] = TEMP_12_BIT;
				break;
			case 11:
				scratchPad[CONFIGURATION] = TEMP_11_BIT;
				break;
			case 10:
				scratchPad[CONFIGURATION] = TEMP_10_BIT;
				break;
			case 9:
			default:
				scratchPad[CONFIGURATION] = TEMP_9_BIT;
				break;
			}
			writeScratchPad(deviceAddress, scratchPad);

			// without calculation we can always set it to max
			bitResolution = max(bitResolution, newResolution);

			if (!skipGlobalBitResolutionCalculation
					&& (bitResolution > newResolution)) {
				bitResolution = newResolution;
				DeviceAddress deviceAddr;
				for (int i = 0; i < devices; i++) {
					getAddress(deviceAddr, i);
					bitResolution = max(bitResolution,
							getResolution(deviceAddr));
				}
			}
		}
		return true;  // new value set
	}

	return false;

}

I don't intend to dig out the Dallas datasheet myself but it's pretty clear that:

	ScratchPad scratchPad;

defines a "scratchpad" which mimics the registers in the device. The code then makes a choice such as:

scratchPad[CONFIGURATION] = TEMP_10_BIT;

which is clearly updating the "CONFIGURATION" entry in that set. Then the code goes on to:

writeScratchPad(deviceAddress, scratchPad);

One would need to fig further in to this code but it seems very easy to read. For example, elsewhere we find a neatly laid out:

// Scratchpad locations
#define TEMP_LSB        0
#define TEMP_MSB        1
#define HIGH_ALARM_TEMP 2
#define LOW_ALARM_TEMP  3
#define CONFIGURATION   4
#define INTERNAL_BYTE   5
#define COUNT_REMAIN    6
#define COUNT_PER_C     7
#define SCRATCHPAD_CRC  8

revealing that "CONFIGURATION" is the 5th byte in the register array.

If pushed still further one might examine:

void DallasTemperature::writeScratchPad(const uint8_t* deviceAddress,
		const uint8_t* scratchPad) {

	_wire->reset();
	_wire->select(deviceAddress);
	_wire->write(WRITESCRATCH);
	_wire->write(scratchPad[HIGH_ALARM_TEMP]); // high alarm temp
	_wire->write(scratchPad[LOW_ALARM_TEMP]); // low alarm temp

	// DS1820 and DS18S20 have no configuration register
	if (deviceAddress[0] != DS18S20MODEL)
		_wire->write(scratchPad[CONFIGURATION]);

	_wire->reset();

	// save the newly written values to eeprom
	_wire->select(deviceAddress);
	_wire->write(COPYSCRATCH, parasite);
	delay(20); // <--- added 20ms delay to allow 10ms long EEPROM write operation (as specified by datasheet)

    if (parasite) {
		activateExternalPullup();
		delay(10); // 10ms delay
		deactivateExternalPullup();
	}
    _wire->reset();

}

That, clearly, is where the actual byte(s) transfer to the device occurs.

EDIT: actually I did go back and look at the datasheet and find:

So I was able to determine the operation of the device purely by reading this C++ code. As such I would suggest it is fairly high quality C++ code if the operation is so clear from a quick scan of the code.