Fix WMath's map() implementation for inverse/round-trip mapping #7027
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| Here's the sketch for testing correctness and timing: uint32_t expired; uint32_t iterations; void setup() { Serial.begin(115200); while (!Serial); Serial.println("check map"); expired = 0; iterations = 0; } constexpr int imin = 0; constexpr int imax = 180; constexpr int omin = 1000; constexpr int omax = 2000; int i = 0; int fails = 0; void loop() { ++iterations; i = (i + 1) % (imax + 1); #if defined(ESP8266) || defined(ESP32) cli(); volatile auto start = ESP.getCycleCount(); #else // Set Timer 1 to normal mode at F_CPU. TCCR1A = 0; TCCR1B = 1; cli(); volatile uint16_t start = TCNT1; #endif volatile auto o = map(i, imin, imax, omin, omax); #if defined(ESP8266) || defined(ESP32) sei(); volatile auto cycles = ESP.getCycleCount() - start; #else sei(); volatile uint16_t finish = TCNT1; uint16_t cycles = finish - start; #endif expired += cycles; if (i != map(o, omin, omax, imin, imax)) { ++fails; } if (iterations > 100000) { Serial.print("Cycles per map(...) = "); Serial.print(expired / iterations); Serial.print(", fails = "); Serial.print(fails); Serial.println(); expired = 0; iterations = 0; fails = 0; } } |
…ion. Greatly reduces error rate (half, or 0 zero errors, depends on in/out ranges) for round-trip mapping at the same performance.
devyte reviewed Feb 9, 2020
| const long divisor = in_max - in_min; | ||
| const long delta = x - in_min; | ||
| | ||
| return (delta * dividend + (divisor / 2)) / divisor + out_min; |
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This doesn't handle divisor == 0.
| This today got merged into Arduino Core for ESP32, espressif/arduino-esp32#3655 |
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Inspired by Servo.cpp's
improved_map, this superseded that code, and has better performance (identical to prior WMath implementation).I expect this is better used to replace the core implementation, then drop "improved_map" from Servo.cpp, than keep it local and have a map() function that may be compatible but works horribly ;-)