50 lines
1.9 KiB
C++
50 lines
1.9 KiB
C++
// tempo — a validated project tempo and every beats <-> seconds <-> ms conversion a
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// beat-denominated capture value resolves through.
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//
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// A BEAT IS A QUARTER NOTE — REAPER states project tempo in quarter notes per minute
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// regardless of time signature, so a division resolves without one.
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#pragma once
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#include <optional>
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#include <type_traits>
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namespace reasampler::instrument::note {
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inline constexpr double kMsPerSecond = 1000.0;
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constexpr double msToSeconds(double ms) { return ms / kMsPerSecond; }
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constexpr double secondsToMs(double seconds) { return seconds * kMsPerSecond; }
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// The largest magnitude, in beats or in milliseconds, the conversions below are required to
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// keep finite. `fromBpm` validates against it and every caller caps its own domain to it, so
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// the two halves of the totality claim meet at one number. Astronomically above anything
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// musical — a billion milliseconds is eleven days — so nothing real is excluded.
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inline constexpr double kMaxConvertibleMagnitude = 1e9;
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class Tempo {
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public:
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// Rejects rather than clamps, alone among this module's doors: an unusable BPM has no
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// nearest usable one to fall to. See this directory's CLAUDE.md for the rule.
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static std::optional<Tempo> fromBpm(double beatsPerMinute);
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double bpm() const { return bpm_; }
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double secondsPerBeat() const;
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double beatsToSeconds(double beats) const;
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double secondsToBeats(double seconds) const;
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double beatsToMs(double beats) const;
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double msToBeats(double ms) const;
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private:
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explicit Tempo(double beatsPerMinute) : bpm_(beatsPerMinute) {}
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double bpm_;
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};
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static_assert(!std::is_default_constructible_v<Tempo>,
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"Tempo must not be constructible without a validated BPM");
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static_assert(!std::is_constructible_v<Tempo, double>,
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"fromBpm must be the only way to give a Tempo a value");
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} // namespace reasampler::instrument::note
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