87 lines
2.8 KiB
C++
87 lines
2.8 KiB
C++
/**
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* @file scaled_channel.h
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*/
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#pragma once
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#include <cmath>
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#include <cstdint>
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#include <type_traits>
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struct scaled_channel_base { };
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template <typename TTest>
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static constexpr bool is_scaled_channel = std::is_base_of_v<scaled_channel_base, TTest>;
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// This class lets us transparently store something at a ratio inside an integer type
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// Just use it like a float - you can read and write to it, like this:
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// scaled_channel<uint8_t, 10> myVar;
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// myVar = 2.4f; // converts to an int, stores 24
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// float x = myVar; // converts back to float, returns 2.4f
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template <typename T, int mul = 1, int div = 1>
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class scaled_channel : scaled_channel_base {
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using TSelf = scaled_channel<T, mul, div>;
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public:
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struct IncompleteType;
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constexpr scaled_channel() : m_value(static_cast<T>(0)) { }
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// Only allow conversion directly to T when mul/div are both 1, otherwise this constructor doesn't exist and the float conversion is used.
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constexpr scaled_channel(std::conditional_t<mul == 1 && div == 1, T, IncompleteType> val) {
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m_value = val;
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}
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// Scale the float in to our scaled channel
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constexpr scaled_channel(std::conditional_t<mul != 1 || div != 1, float, IncompleteType> val) {
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// If there are scale factors, it must NOT be a float. Why would you scale a float?
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static_assert(std::is_integral_v<T>);
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m_value = std::roundf(val * float(mul) / div);
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}
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// Only allow conversion directly to T when mul/div are both 1, otherwise this operator doesn't exist and the float conversion is used.
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constexpr operator typename std::conditional_t<mul == 1 && div == 1, T, IncompleteType>() const {
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return m_value;
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}
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// Allow reading back out as a float (note: this may be lossy!)
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constexpr operator typename std::conditional_t<mul != 1 || div != 1, float, IncompleteType>() const {
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return m_value * (float(div) / mul);
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}
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// Postfix increment operator
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// only enable if:
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// - base type T is an integral type (integer)
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// - multiplier is equal to 1
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void operator++(int) {
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static_assert(mul == 1 && div == 1,
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"Increment operator only supported for non-scaled integer types");
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static_assert(std::is_integral_v<T>, "Increment operator only supported for non-scaled integer types");
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m_value++;
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}
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constexpr const char* getFirstByteAddr() const {
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return &m_firstByte;
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}
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private:
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union {
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T m_value;
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char m_firstByte;
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};
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};
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// We need to guarantee that scaled values containing some type are the same size
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// as that underlying type. We rely on the class only having a single member for
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// this trick to work.
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static_assert(sizeof(scaled_channel<uint8_t>) == 1);
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static_assert(sizeof(scaled_channel<uint16_t>) == 2);
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static_assert(sizeof(scaled_channel<uint32_t>) == 4);
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static_assert(sizeof(scaled_channel<float>) == 4);
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// make sure the scaled channel detector works
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static_assert(!is_scaled_channel<int>);
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static_assert(is_scaled_channel<scaled_channel<int, 5>>);
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