Merge pull request #2188 from AllenInstitute/bugfix/2188-fix_popcount

Utils: fix function popcount for argument < 0

Packages/MIES/MIES_Utilities_Numeric.ipf

@@ -70,19 +70,26 @@ threadsafe Function ClearBit(var, bit)
 End
 
 /// @brief Count the number of ones in `value`
+///        Note: if the argument given is not an unsigned int64
+///        then it will be implicitly converted to an uint64.
+///        This mean e.g. for a double precision argument that
+///        the maximum number of bits for positive numbers is 53 from 2^53 - 1
+///        and for negative numbers the result is always >= 11.
 ///
-/// @param value will be truncated to an integer value
-Function PopCount(value)
-	variable value
+/// @param value will be truncated to an 64 bit unsigned integer value
+Function PopCount(uint64 value)
 
 	variable count
+	uint64   leftSideHelper
+
+	if(value == 0)
+		return 0
+	endif
 
-	value = trunc(value)
 	do
-		if(value & 1)
-			count += 1
-		endif
-		value = trunc(value / 2^1) // shift one to the right
+		leftSideHelper = value & 1
+		count         += leftSideHelper
+		value          = value >> 1
 	while(value > 0)
 
 	return count

Packages/tests/Basic/UTF_Utils.ipf

@@ -8621,3 +8621,29 @@ static Function FND_Works()
 	WAVE/Z result = FindNeighbourDuplicates({1, NaN, NaN, Inf, -Inf, Inf, Inf, 2})
 	CHECK_EQUAL_WAVES(result, {2, 6}, mode = WAVE_DATA)
 End
+
+static Function PopCount_Works()
+
+	uint64 ui
+
+	CHECK_EQUAL_VAR(PopCount(0), 0)
+	CHECK_EQUAL_VAR(PopCount(1), 1)
+	CHECK_EQUAL_VAR(PopCount(2), 1)
+	CHECK_EQUAL_VAR(PopCount(3), 2)
+	CHECK_EQUAL_VAR(PopCount(7), 3)
+	CHECK_EQUAL_VAR(PopCount(15), 4)
+	// negative numbers are represented as two's complement
+	CHECK_EQUAL_VAR(PopCount(-1), 64)
+	CHECK_EQUAL_VAR(PopCount(-2), 63)
+	CHECK_EQUAL_VAR(PopCount(-3), 63)
+	CHECK_EQUAL_VAR(PopCount(-4), 62)
+	// non-finite numbers get implicitly converted to 0x8000000000000000
+	CHECK_EQUAL_VAR(PopCount(NaN), 1)
+	CHECK_EQUAL_VAR(PopCount(Inf), 1)
+	CHECK_EQUAL_VAR(PopCount(-Inf), 1)
+	// tests when no implicit conversion takes place
+	ui = 0xAAAAAAAAAAAAAAAA
+	CHECK_EQUAL_VAR(PopCount(ui), 32)
+	ui = 0x5555555555555555
+	CHECK_EQUAL_VAR(PopCount(ui), 32)
+End