Bug: Unexpected values when using Arduino Leonardo #3
Comments
satoer
changed the title
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Just tried the same code on a ESP32. This resulted in the expected outcome: truncated for readability |
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Hi Satoer, The explanation is probably quite simple, the size of an int is 16 bit on a Leonardo and 32 bit on an ESP32 you can verify my hypothesis with the sketch below. void setup()
{
Serial.begin(115200);
Serial.println(sizeof(int));
}
void loop()
{}Solution for your sketch #include "MultiMap.h"
int32 In[] = { 0 , 512};
int32 Out[] = { 0 , 255};
void setup() {
Serial.begin(9600);
}
void loop() {
for (int i = 0; i <= 512; i++) {
int mapValue = multiMap<int32>(i, In, Out, 2); // <<<<<<<<<<< make it explicit 32 bits integers.
Serial.println(String(i) + ": " + String (mapValue));
}
delay(10000);
} |
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We can try to check the input value of 129 (which was the first to fail int In[] = { 0 , 512}; As there is only one segment, the output = outmin + (input * (outmax - outmin)) / (inmax - in min) output = 0 + (129 * ( 255 - 0)) / (512- 0) 32895 flips to - (65535 - 32685) = -32640 output = -32640 /512 So always check intermediate math results if unexpected values pop up (even when most look OK). |
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First code had output: 2 Second code received an error: Changed every 'int32' to 'long' and it fixed the problem! The outcome is as suspected. Thank you, this was driving me crazy. |
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should been long is 32 bit on Leonardo and I expect too on ESP. These 'intermediate overflows' happen sometimes when porting code or when mixing unsigned and signed math. |
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Similar things can happen when e.g. a time variable overflows, most famous is millis() after some 49.7 days. or micros() after ~70 minutes. If you math is not prepared to handle the overflows correctly strange values may pop up. Recently I read about a bug that occurred every ~25 days, which was almost in sync with the moon cycle so people were quite amazed. In the end it was a mix of millis() overflow combined with signed/unsigned math mixture. |
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Thanks Rob, You've been really helpful, and got my program working. Didn't suspected a overflow because the values are well below a 16 bit integer. I didn't took intermediate results in consideration though. |
I don't get it. Used Multimap several times before with great success, but now with an Arduino Leonardo I get unexpected results.
I've made an example to the bear minimum:
And this is the result:
Any idea why the output does not met the expectation?
added cpp in the code block markup for syntax highlighting
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