ipa: rkisp1: Add a helper to convert floating-point to fixed-point

Add helper functions for converting between floating point and fixed
point numbers. Also add tests for them.

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>

src/ipa/rkisp1/meson.build

@@ -8,6 +8,7 @@ ipa_name = 'ipa_rkisp1'
 rkisp1_ipa_sources = files([
     'ipa_context.cpp',
     'rkisp1.cpp',
+    'utils.cpp',
 ])
 
 rkisp1_ipa_sources += rkisp1_ipa_algorithms

src/ipa/rkisp1/utils.cpp

@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Paul Elder <paul.elder@ideasonboard.com>
+ *
+ * Miscellaneous utility functions specific to rkisp1
+ */
+
+#include "utils.h"
+
+/**
+ * \file utils.h
+ */
+
+namespace libcamera {
+
+namespace ipa::rkisp1::utils {
+
+/**
+ * \fn R floatingToFixedPoint(T number)
+ * \brief Convert a floating point number to a fixed-point representation
+ * \tparam I Bit width of the integer part of the fixed-point
+ * \tparam F Bit width of the fractional part of the fixed-point
+ * \tparam R Return type of the fixed-point representation
+ * \tparam T Input type of the floating point representation
+ * \param number The floating point number to convert to fixed point
+ * \return The converted value
+ */
+
+/**
+ * \fn R fixedToFloatingPoint(T number)
+ * \brief Convert a fixed-point number to a floating point representation
+ * \tparam I Bit width of the integer part of the fixed-point
+ * \tparam F Bit width of the fractional part of the fixed-point
+ * \tparam R Return type of the floating point representation
+ * \tparam T Input type of the fixed-point representation
+ * \param number The fixed point number to convert to floating point
+ * \return The converted value
+ */
+
+} /* namespace ipa::rkisp1::utils */
+
+} /* namespace libcamera */

src/ipa/rkisp1/utils.h

@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Paul Elder <paul.elder@ideasonboard.com>
+ *
+ * Miscellaneous utility functions specific to rkisp1
+ */
+
+#pragma once
+
+#include <cmath>
+#include <limits>
+#include <type_traits>
+
+namespace libcamera {
+
+namespace ipa::rkisp1::utils {
+
+#ifndef __DOXYGEN__
+template<unsigned int I, unsigned int F, typename R, typename T,
+	 std::enable_if_t<std::is_integral_v<R> &&
+			  std::is_floating_point_v<T>> * = nullptr>
+#else
+template<unsigned int I, unsigned int F, typename R, typename T>
+#endif
+constexpr R floatingToFixedPoint(T number)
+{
+	static_assert(sizeof(int) >= sizeof(R));
+	static_assert(I + F <= sizeof(R) * 8);
+
+	/*
+	 * The intermediate cast to int is needed on arm platforms to properly
+	 * cast negative values. See
+	 * https://embeddeduse.com/2013/08/25/casting-a-negative-float-to-an-unsigned-int/
+	 */
+	R mask = (1 << (F + I)) - 1;
+	R frac = static_cast<R>(static_cast<int>(std::round(number * (1 << F)))) & mask;
+
+	return frac;
+}
+
+#ifndef __DOXYGEN__
+template<unsigned int I, unsigned int F, typename R, typename T,
+	 std::enable_if_t<std::is_floating_point_v<R> &&
+			  std::is_integral_v<T>> * = nullptr>
+#else
+template<unsigned int I, unsigned int F, typename R, typename T>
+#endif
+constexpr R fixedToFloatingPoint(T number)
+{
+	static_assert(sizeof(int) >= sizeof(T));
+	static_assert(I + F <= sizeof(T) * 8);
+
+	/*
+	 * Recreate the upper bits in case of a negative number by shifting the sign
+	 * bit from the fixed point to the first bit of the unsigned and then right shifting
+	 * by the same amount which keeps the sign bit in place.
+	 * This can be optimized by the compiler quite well.
+	 */
+	int remaining_bits = sizeof(int) * 8 - (I + F);
+	int t = static_cast<int>(static_cast<unsigned>(number) << remaining_bits) >> remaining_bits;
+	return static_cast<R>(t) / static_cast<R>(1 << F);
+}
+
+} /* namespace ipa::rkisp1::utils */
+
+} /* namespace libcamera */

test/ipa/meson.build

@@ -1,5 +1,7 @@
 # SPDX-License-Identifier: CC0-1.0
 
+subdir('rkisp1')
+
 ipa_test = [
     {'name': 'ipa_module_test', 'sources': ['ipa_module_test.cpp']},
     {'name': 'ipa_interface_test', 'sources': ['ipa_interface_test.cpp']},

test/ipa/rkisp1/meson.build

@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: CC0-1.0
+
+rkisp1_ipa_test = [
+    {'name': 'rkisp1-utils', 'sources': ['rkisp1-utils.cpp']},
+]
+
+foreach test : rkisp1_ipa_test
+    exe = executable(test['name'], test['sources'], libcamera_generated_ipa_headers,
+                     dependencies : libcamera_private,
+                     link_with : [libipa, test_libraries],
+                     include_directories : [libipa_includes, test_includes_internal,
+                                            '../../../src/ipa/rkisp1/'])
+
+    test(test['name'], exe, suite : 'ipa')
+endforeach

test/ipa/rkisp1/rkisp1-utils.cpp

@@ -0,0 +1,88 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2024, Paul Elder <paul.elder@ideasonboard.com>
+ *
+ * Miscellaneous utility tests
+ */
+
+#include <cmath>
+#include <iostream>
+#include <map>
+#include <stdint.h>
+
+#include "../src/ipa/rkisp1/utils.h"
+
+#include "test.h"
+
+using namespace std;
+using namespace libcamera;
+using namespace ipa::rkisp1;
+
+class RkISP1UtilsTest : public Test
+{
+protected:
+	template<unsigned int intPrec, unsigned fracPrec, typename T>
+	int testSingleFixedPoint(double input, T expected)
+	{
+		T ret = utils::floatingToFixedPoint<intPrec, fracPrec, T>(input);
+		if (ret != expected) {
+			cerr << "Expected " << input << " to convert to "
+			     << expected << ", got " << ret << std::endl;
+			return TestFail;
+		}
+
+		/*
+		 * The precision check is fairly arbitrary but is based on what
+		 * the rkisp1 is capable of in the crosstalk module.
+		 */
+		double f = utils::fixedToFloatingPoint<intPrec, fracPrec, double>(ret);
+		if (std::abs(f - input) > 0.005) {
+			cerr << "Reverse conversion expected " << ret
+			     << " to convert to " << input
+			     << ", got " << f << std::endl;
+			return TestFail;
+		}
+
+		return TestPass;
+	}
+
+	int testFixedPoint()
+	{
+		/*
+		 * The second 7.992 test is to test that unused bits don't
+		 * affect the result.
+		 */
+		std::map<double, uint16_t> testCases = {
+			{ 7.992, 0x3FF },
+			{ 7.992, 0xBFF },
+			{   0.2, 0x01A },
+			{  -0.2, 0x7E6 },
+			{  -0.8, 0x79A },
+			{  -0.4, 0x7CD },
+			{  -1.4, 0x74D },
+			{    -8, 0x400 },
+			{     0, 0 },
+		};
+
+		int ret;
+		for (const auto &testCase : testCases) {
+			ret = testSingleFixedPoint<4, 7, uint16_t>(testCase.first,
+								   testCase.second);
+			if (ret != TestPass)
+				return ret;
+		}
+
+		return TestPass;
+	}
+
+	int run()
+	{
+		/* fixed point conversion test */
+		if (testFixedPoint() != TestPass)
+			return TestFail;
+
+		return TestPass;
+	}
+};
+
+TEST_REGISTER(RkISP1UtilsTest)