libcamera: src/ipa/libipa/fixedpoint.h Source File

libcamera v0.5.1 Supporting cameras in Linux since 2019 |

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fixedpoint.h
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1/* SPDX-License-Identifier: LGPL-2.1-or-later */
2/*
3 * Copyright (C) 2024, Paul Elder <paul.elder@ideasonboard.com>
4 *
5 * Fixed / floating point conversions
6 */
7
8#pragma once
9
10#include <cmath>
11#include <type_traits>
12
13namespace libcamera {
14
15namespace ipa {
16
17#ifndef __DOXYGEN__
18template<unsigned int I, unsigned int F, typename R, typename T,
19 std::enable_if_t<std::is_integral_v<R> &&
20 std::is_floating_point_v<T>> * = nullptr>
21#else
22template<unsigned int I, unsigned int F, typename R, typename T>
23#endif
24 constexpr R floatingToFixedPoint(T number)
25{
26 static_assert(sizeof(int) >= sizeof(R));
27 static_assert(I + F <= sizeof(R) * 8);
28
29 /*
30 * The intermediate cast to int is needed on arm platforms to properly
31 * cast negative values. See
32 * https://embeddeduse.com/2013/08/25/casting-a-negative-float-to-an-unsigned-int/
33 */
34 R mask = (1 << (F + I)) - 1;
35 R frac = static_cast<R>(static_cast<int>(std::round(number * (1 << F)))) & mask;
36
37 return frac;
38}
39
40#ifndef __DOXYGEN__
41template<unsigned int I, unsigned int F, typename R, typename T,
42 std::enable_if_t<std::is_floating_point_v<R> &&
43 std::is_integral_v<T>> * = nullptr>
44#else
45template<unsigned int I, unsigned int F, typename R, typename T>
46#endif
47 constexpr R fixedToFloatingPoint(T number)
48{
49 static_assert(sizeof(int) >= sizeof(T));
50 static_assert(I + F <= sizeof(T) * 8);
51
52 /*
53 * Recreate the upper bits in case of a negative number by shifting the sign
54 * bit from the fixed point to the first bit of the unsigned and then right shifting
55 * by the same amount which keeps the sign bit in place.
56 * This can be optimized by the compiler quite well.
57 */
58 int remaining_bits = sizeof(int) * 8 - (I + F);
59 int t = static_cast<int>(static_cast<unsigned>(number) << remaining_bits) >> remaining_bits;
60 return static_cast<R>(t) / static_cast<R>(1 << F);
61}
62
63} /* namespace ipa */
64
65} /* 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