[PATCH v2] libcamera: utils: Add a helper to convert floating-point to fixed-point
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Wed Apr 24 09:51:08 CEST 2024
Hi Paul,
Thank you for the patch.
On Wed, Apr 24, 2024 at 04:44:09PM +0900, Paul Elder wrote:
> Add helper functions for converting between floating point and fixed
> point numbers. Also add tests for them.
>
> Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>
> ---
> Changes in v2:
> - added the reverse conversion function (fixed -> floating)
> - added tests
> - make the conversion code cleaner
> ---
> include/libcamera/base/utils.h | 37 +++++++++++++++++++++++++
> src/libcamera/base/utils.cpp | 20 ++++++++++++++
> test/utils.cpp | 49 ++++++++++++++++++++++++++++++++++
I envision more math-related helpers in the future. Could we gather
those in a new include/libcamera/base/math.h header ?
> 3 files changed, 106 insertions(+)
>
> diff --git a/include/libcamera/base/utils.h b/include/libcamera/base/utils.h
> index 37d9af60..da0767e3 100644
> --- a/include/libcamera/base/utils.h
> +++ b/include/libcamera/base/utils.h
> @@ -9,6 +9,7 @@
>
> #include <algorithm>
> #include <chrono>
> +#include <cmath>
> #include <iterator>
> #include <memory>
> #include <ostream>
> @@ -369,6 +370,42 @@ decltype(auto) abs_diff(const T &a, const T &b)
>
> double strtod(const char *__restrict nptr, char **__restrict endptr);
>
> +#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(I + F <= sizeof(R) * 8);
> +
> + R maskI = (1 << I) - 1;
> + R whole = (static_cast<R>(number) & maskI) << F;
> +
> + R maskF = (1 << F) - 1;
> + R frac = static_cast<R>(std::round(number * (1 << F))) & maskF;
> +
> + return whole | 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(I + F <= sizeof(T) * 8);
> +
> + int coeff = number >> (I + F - 1) ? -1 : 1;
> +
> + return coeff * static_cast<R>(number) / static_cast<R>(1 << F);
> +}
> +
> } /* namespace utils */
>
> #ifndef __DOXYGEN__
> diff --git a/src/libcamera/base/utils.cpp b/src/libcamera/base/utils.cpp
> index 3b73b442..ba36026d 100644
> --- a/src/libcamera/base/utils.cpp
> +++ b/src/libcamera/base/utils.cpp
> @@ -521,6 +521,26 @@ double strtod(const char *__restrict nptr, char **__restrict endptr)
> #endif
> }
>
> +/**
> + * \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
> + * \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
> + * \return The converted value
> + */
> +
> } /* namespace utils */
>
> #ifndef __DOXYGEN__
> diff --git a/test/utils.cpp b/test/utils.cpp
> index fc56e14e..f1805207 100644
> --- a/test/utils.cpp
> +++ b/test/utils.cpp
> @@ -170,6 +170,51 @@ protected:
> return TestPass;
> }
>
> + 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) > 0.001) {
> + cerr << "Reverse conversion expected " << ret
> + << " to convert to " << input
> + << ", got " << f << std::endl;
> + return TestFail;
> + }
> +
> + return TestPass;
> + }
> +
> + int testFixedPoint()
> + {
> + /* These are the only cases that we know for certain */
> + std::map<double, uint16_t> testCases = {
> + { 7.992, 0x3FF },
> + { -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()
> {
> /* utils::hex() test. */
> @@ -290,6 +335,10 @@ protected:
> if (testDuration() != TestPass)
> return TestFail;
>
> + /* fixed point conversion test */
> + if (testFixedPoint() != TestPass)
> + return TestFail;
> +
> return TestPass;
> }
> };
--
Regards,
Laurent Pinchart
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