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fixedpoint.h
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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
* Copyright (C) 2024, Paul Elder <paul.elder@ideasonboard.com>
*
* Fixed / floating point conversions
*/
#pragma once
#include <cmath>
#include <type_traits>
namespace libcamera {
namespace ipa {
#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 */
} /* namespace libcamera */
libcamera::ipa
The IPA (Image Processing Algorithm) namespace.
Definition af.cpp:58
libcamera::ipa::fixedToFloatingPoint
constexpr R fixedToFloatingPoint(T number)
Convert a fixed-point number to a floating point representation.
Definition fixedpoint.h:47
libcamera::ipa::floatingToFixedPoint
constexpr R floatingToFixedPoint(T number)
Convert a floating point number to a fixed-point representation.
Definition fixedpoint.h:24
libcamera
Top-level libcamera namespace.
Definition backtrace.h:17