Improve map() function

https://forum.pjrc.com/threads/63230-map()-returns-different-values-on-arduino-vs-teensy
PaulStoffregen · Oct 22, 2020 · 92b126d · 92b126d
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commit 92b126d
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Showing 2 changed files with 46 additions and 6 deletions.
diff --git a/teensy3/wiring.h b/teensy3/wiring.h
@@ -49,15 +49,35 @@ long map(T _x, A _in_min, B _in_max, C _out_min, D _out_max, typename std::enabl
 {
 	long x = _x, in_min = _in_min, in_max = _in_max, out_min = _out_min, out_max = _out_max;
 	// Arduino's traditional algorithm
-	//return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
+#if 0
+	return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
+#endif
+#if 0
 	// st42's suggestion: https://github.com/arduino/Arduino/issues/2466#issuecomment-69873889
-	// more conversation:
-	// https://forum.pjrc.com/threads/44503-map()-function-improvements
 	if ((in_max - in_min) > (out_max - out_min)) {
 		return (x - in_min) * (out_max - out_min+1) / (in_max - in_min+1) + out_min;
 	} else {
 		return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
 	}
+#endif
+	long in_range = in_max - in_min;
+	long out_range = out_max - out_min;
+	if (in_range == 0) return out_min + out_range / 2;
+	long num = (x - in_min) * out_range;
+	if (out_range >= 0) {
+		num += in_range / 2;
+	} else {
+		num -= in_range / 2;
+	}
+	long result = num / in_range + out_min;
+	if (out_range >= 0) {
+		if (in_range * num < 0) return result - 1;
+	} else {
+		if (in_range * num >= 0) return result + 1;
+	}
+	return result;
+	// more conversation:
+	// https://forum.pjrc.com/threads/44503-map()-function-improvements
 }
 // when the input is a float or double, do all math using the input's type
 template <class T, class A, class B, class C, class D>

diff --git a/teensy4/wiring.h b/teensy4/wiring.h
@@ -49,15 +49,35 @@ long map(T _x, A _in_min, B _in_max, C _out_min, D _out_max, typename std::enabl
 {
 	long x = _x, in_min = _in_min, in_max = _in_max, out_min = _out_min, out_max = _out_max;
 	// Arduino's traditional algorithm
-	//return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
+#if 0
+	return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
+#endif
+#if 0
 	// st42's suggestion: https://github.com/arduino/Arduino/issues/2466#issuecomment-69873889
-	// more conversation:
-	// https://forum.pjrc.com/threads/44503-map()-function-improvements
 	if ((in_max - in_min) > (out_max - out_min)) {
 		return (x - in_min) * (out_max - out_min+1) / (in_max - in_min+1) + out_min;
 	} else {
 		return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
 	}
+#endif
+	long in_range = in_max - in_min;
+	long out_range = out_max - out_min;
+	if (in_range == 0) return out_min + out_range / 2;
+	long num = (x - in_min) * out_range;
+	if (out_range >= 0) {
+		num += in_range / 2;
+	} else {
+		num -= in_range / 2;
+	}
+	long result = num / in_range + out_min;
+	if (out_range >= 0) {
+		if (in_range * num < 0) return result - 1;
+	} else {
+		if (in_range * num >= 0) return result + 1;
+	}
+	return result;
+	// more conversation:
+	// https://forum.pjrc.com/threads/44503-map()-function-improvements
 }
 // when the input is a float or double, do all math using the input's type
 template <class T, class A, class B, class C, class D>