Serial.print a NaN

[Jake]

I spent the day tracking down a divide by zero error. (I know I am complaining.) I am using a teensy 3.1 on Arduino 1.6.5 and Teensyduino 1.25-Beta2 on Ubuntu.

So this is a combination bug report and enhancement request for Serial.print().

What finally clued me in is that when my error occurred and Serial.print printed out a zero for the number, the cosf(num) was also zero. Finally I started searching and found Serial.print in line 726 of my revisions.txt file on version 1.6.5. This applies to Arduino 1.0.2. It references the following links:

https://code.google.com/p/arduino/issues/detail?id=946
https://code.google.com/p/arduino/issues/detail?id=961
https://code.google.com/p/arduino/issues/detail?id=967

This indicates that NaN should be printed out. To check things out I wrote some code to see how things work.

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  delay(2000);
  float i;
  for (i = 0; i <= 40; i++) {
    Serial.print(i / 10);
    Serial.print("\t");
    Serial.print(cosf(i / 10.0));
    Serial.println();
  }

  Serial.println();
  Serial.println();

  float a = 0.0 / 0.0;
  float b = 1 / 0 / 0.0;
  float c = 1e-35;
  float d = 1e35;
  float e = 1e-350;
  float f = 1e350;

  Serial.print(a);
  Serial.print("\t");
  Serial.print(cosf(a));
  Serial.print("\t");
  Serial.print(isinf(a) ? "inf" : "fin");
  Serial.print("\t");
  Serial.println(isnan(a) ? "nan" : "num");
  Serial.print(b);
  Serial.print("\t");
  Serial.print(cosf(b));
  Serial.print("\t");
  Serial.print(isinf(b) ? "inf" : "fin");
  Serial.print("\t");
  Serial.println(isnan(b) ? "nan" : "num");
  Serial.print(c);
  Serial.print("\t");
  Serial.print(cosf(c));
  Serial.print("\t");
  Serial.print(isinf(c) ? "inf" : "fin");
  Serial.print("\t");
  Serial.println(isnan(c) ? "nan" : "num");
  Serial.print(d);
  Serial.print("\t");
  Serial.print(cosf(d));
  Serial.print("\t");
  Serial.print(isinf(d) ? "inf" : "fin");
  Serial.print("\t");
  Serial.println(isnan(d) ? "nan" : "num");
  Serial.print(e);
  Serial.print("\t");
  Serial.print(cosf(e));
  Serial.print("\t");
  Serial.print(isinf(e) ? "inf" : "fin");
  Serial.print("\t");
  Serial.println(isnan(e) ? "nan" : "num");
  Serial.print(f);
  Serial.print("\t");
  Serial.print(cosf(f));
  Serial.print("\t");
  Serial.print(isinf(f) ? "inf" : "fin");
  Serial.print("\t");
  Serial.println(isnan(f) ? "nan" : "num");

}

void loop() {
  // put your main code here, to run repeatedly:

}

Which gives the result

0.00	1.00
0.10	1.00
0.20	0.98
0.30	0.96
0.40	0.92


0.00	0.00	fin	nan
0.00	0.00	fin	nan
0.00	1.00	fin	num
4294967295.//	-0.04	fin	num
0.00	1.00	fin	num
4294967295.//	0.00	inf	num

Hopefully the Teensy Serial.print function will be able to print out overflow, underflow, exponential notation would be nice, but at least NaN and Inf (though I did not get an inf with this test).