Potential bug in min(), max(), abs(), constrain(), round(), sq() macros when using with function call

[chill-cats]

In Arduino.h header file, there are these macro

#define min(a,b) ((a)<(b)?(a):(b))
#define max(a,b) ((a)>(b)?(a):(b))
#define abs(x) ((x)>0?(x):-(x))
#define constrain(amt,low,high) ((amt)<(low)?(low):((amt)>(high)?(high):(amt)))
#define round(x)     ((x)>=0?(long)((x)+0.5):(long)((x)-0.5))
#define sq(x) ((x)*(x))

When using these macros with function calls, the function get called twice (or multiple times), which cause potential bug (when function return different value) Simple test program which show this bug

#include <Arduino.h>
void setup() {
    Serial.begin(9600);
}

void loop() {
    for (int i = 0; i < 20; i++) {
        Serial.println(max(rand() % 10, 5));
    }
    while (true) {
        // stop
    }
}

Reference: https://www.youtube.com/watch?v=j0_u26Vpb4w&t=632s

[per1234]

Note that, as discussed at https://github.com/arduino/ArduinoCore-API/issues/85, this issue has already been resolved for min and max in arduino/ArduinoCore-API:

https://github.com/arduino/ArduinoCore-API/blob/82a5055a0588976c8df8c1ff3d978f62d68410f3/api/Common.h#L124-L149

So it would be partially resolved by migrating this core to using ArduinoCore-API (https://github.com/arduino/ArduinoCore-avr/pull/329)

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The Arduino Language Reference does warn about this problem: https://github.com/arduino/reference-en/pull/513