Problem with abs()

Using Arduino Programming Questions
#1

Hi, the function abs has an unexpected behavior when work with uint32_t. Run example:

void setup() {
  Serial.begin(9600);

   uint32_t oldTs = 100;
   uint32_t newTs = 50;
  
  int32_t diffTs = abs(newTs - oldTs);
  Serial.print("La diferencia es: "); 
  Serial.println(diffTs);
  
  diffTs = abs(diffTs);
  Serial.print("La diferencia es: "); 
  Serial.println(diffTs);

}

void loop() {
  // put your main code here, to run repeatedly:
  delay(10);
}

The output is:

La diferencia es: -50
La diferencia es: 50
#2

abs() is working fine, the unexpected value results from your conversion from uint32_t to int32_t.

This should make things clear:

void setup() {
  Serial.begin(9600);

   uint32_t oldTs = 100;
   uint32_t newTs = 50;
 
  uint32_t diffTs = abs(newTs - oldTs);
  Serial.print("La diferencia (uint32_t) es: ");
  Serial.println(diffTs);
 
  Serial.print("La diferencia (int32_t) es: ");
  Serial.println((int32_t)diffTs);

  diffTs = abs(diffTs);
  Serial.print("La diferencia es: ");
  Serial.println(diffTs);

}

void loop() {
  // put your main code here, to run repeatedly:
  delay(10);
}
#3

Notes and Warnings

Because of the way the abs() function is implemented, avoid using other functions inside the brackets, it may lead to incorrect results.

source abs() - Arduino Reference

#4

The abs() function is a standard (abs - C++ Reference) and it is in the compiler. So everything should be fine.
Then Arduino destroys the standard by adding a abs() macro for no good reason.
They don't want to fix this mistake because the wrong use of abs() might be used in a library.
The same for round(): round() macro in Arduino.h · Issue #76 · arduino/ArduinoCore-API · GitHub.

By the way, pert is right. You should make it signed before calling abs().

#5