Add a description to celsiusToRaw

Author: mkrzewic

DallasTemperature.cpp

@@ -745,10 +745,17 @@ float DallasTemperature::rawToCelsius(int16_t raw) {
 
 }
 
-    // convert from Celsius to raw
+// Convert from Celsius to raw returns temperature in raw integer format.
+// The rounding error in the conversion is smaller than 0.01°C
+// where the resolution of the sensor is at best 0.0625°C (in 12 bit mode).
+// Rounding error can be verified by running:
+//  for (float t=-55.; t<125.; t+=0.01)
+//  {
+//    Serial.println( DallasTemperature::rawToCelsius(DallasTemperature::celsiusToRaw(t))-t, 4 );
+//  }
 int16_t DallasTemperature::celsiusToRaw(float celsius) {
 
-    return static_cast<uint16_t>( celsius * 128.f );  //this just discards of the decimal part (rounds towards zero)
+    return static_cast<uint16_t>( celsius * 128.f );
 }
 
 // convert from raw to Fahrenheit