56 lines
2.0 KiB
C++
56 lines
2.0 KiB
C++
#pragma once
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#include <cstddef>
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#include <cstdint>
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#include <random>
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#include <string>
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#include <type_traits>
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#include <QPoint>
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#include <QPointF>
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#include <QVector2D>
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// FNV-1a 64-bit accumulator used to fingerprint simulation state for
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// determinism verification (see docs/replay_design.md "Determinism").
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//
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// Subsystems contribute their own state through appendChecksum(Hasher&) so the
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// hash stays close to the data it covers and no state knowledge is duplicated.
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// The accumulator is order-sensitive; callers fold state in a deterministic
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// order (sorted containers, fixed view iteration).
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class Hasher
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{
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public:
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// Folds raw bytes into the running hash.
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void appendBytes(const void* data, std::size_t byteCount);
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// Trivially-copyable scalars (ints, enums) are hashed by object representation.
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// Floating-point and Qt types have dedicated overloads below and bypass this.
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template <typename T>
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void append(const T& value)
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{
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static_assert(std::is_trivially_copyable<T>::value,
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"Hasher::append requires a trivially copyable type "
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"(add a dedicated overload otherwise)");
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appendBytes(&value, sizeof(T));
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}
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// Floats are hashed by bit pattern so equal values always hash equally;
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// negative zero is normalized so -0.0 and +0.0 collapse to one value.
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void append(float value);
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void append(double value);
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void append(const QPoint& point);
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void append(const QPointF& point);
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void append(const QVector2D& vector);
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void append(const std::string& text);
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std::uint64_t getValue() const { return m_state; }
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private:
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std::uint64_t m_state = 14695981039346656037ull; // FNV-1a 64-bit offset basis
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};
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// Folds the full mt19937 internal state into a 64-bit fingerprint. mt19937 has a
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// portable, bit-identical text serialization, so this fingerprint is stable
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// across platforms (see docs/replay_design.md "Cross-platform").
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std::uint64_t fingerprintRng(const std::mt19937& rng);
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