test: ipa: rkisp1: utils: Fix floating and fixed point conversion test

There was an issue where using map to store the test cases meant that
the test for ignoring unused bits was skipped because of clashing keys.
Fix this by moving the offending test out of the loop.

While at it, also change the arbitrary floating comparison precision to
be more precise.

Also fix a missing documentation brief.

Fixes: 9d152e9c66 ("ipa: rkisp1: Add a helper to convert floating-point to fixed-point")
Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

test/ipa/rkisp1/rkisp1-utils.cpp

@@ -21,7 +21,23 @@ using namespace ipa::rkisp1;
 class RkISP1UtilsTest : public Test
 {
 protected:
-	template<unsigned int IntPrec, unsigned FracPrec, typename T>
+	/* R for real, I for integer */
+	template<unsigned int IntPrec, unsigned int FracPrec, typename I, typename R>
+	int testFixedToFloat(I input, R expected)
+	{
+		R out = utils::fixedToFloatingPoint<IntPrec, FracPrec, R>(input);
+		R prec = 1.0 / (1 << FracPrec);
+		if (std::abs(out - expected) > prec) {
+			cerr << "Reverse conversion expected " << input
+			     << " to convert to " << expected
+			     << ", got " << out << std::endl;
+			return TestFail;
+		}
+
+		return TestPass;
+	}
+
+	template<unsigned int IntPrec, unsigned int FracPrec, typename T>
 	int testSingleFixedPoint(double input, T expected)
 	{
 		T ret = utils::floatingToFixedPoint<IntPrec, FracPrec, T>(input);
@@ -54,7 +70,6 @@ protected:
 		 */
 		std::map<double, uint16_t> testCases = {
 			{ 7.992, 0x3ff },
-			{ 7.992, 0xbff },
 			{   0.2, 0x01a },
 			{  -0.2, 0x7e6 },
 			{  -0.8, 0x79a },
@@ -72,6 +87,11 @@ protected:
 				return ret;
 		}
 
+		/* Special case with a superfluous one in the unused bits */
+		ret = testFixedToFloat<4, 7, uint16_t, double>(0xbff, 7.992);
+		if (ret != TestPass)
+			return ret;
+
 		return TestPass;
 	}