Alexander
39 lines
2.0 KiB
Go
39 lines
2.0 KiB
Go
// Copyright (C) MongoDB, Inc. 2026-present.
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may
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// not use this file except in compliance with the License. You may obtain
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// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
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// Package binaryutil provides functions for reading binary primitives from
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// byte slices. It is used internally for BSON parsing and wire protocol
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// operations.
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//
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// The functions in this package are designed for use in BSON operations.
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// Signed integer functions (ReadI32, ReadI64) use manual bit-shifting rather
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// than encoding/binary to avoid unsafe signed/unsigned conversions and comply
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// with gosec G115. Bounds-check elimination (BCE) hints help the compiler
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// inline these functions.
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//
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// Benchmarking across different ARM64 architectures (Apple M-series)
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// revealed non-deterministic performance discrepancies between using the
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// "encoding/binary" standard library and manual bit-shifting ("straight-lining").
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//
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// Without Loss of Generality (WLOG), benchmarking observed that:
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// - On Apple M1 Pro: Standard library (ReadU32) outperformed manual
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// bit-shifting (ReadI32) by ~2x (~0.08ns vs ~0.16ns).
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// - On Apple M4 Max: Manual bit-shifting (ReadI32) outperformed the
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// standard library (ReadU32) by ~1.6x (~0.03ns vs ~0.05ns).
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//
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// Further testing showed that "straight-lining" the ReadU32 implementation
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// to match ReadI32 normalized performance to ~0.03ns on the M4 Max, even
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// though the generated assembly for both approaches is virtually equivalent.
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//
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// The generated assembly is nearly identical for both approaches. These
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// sub-nanosecond variations likely stem from microarchitecture differences
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// (instruction caching, branch prediction) rather than the code itself.
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//
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// Since network I/O dominates driver latency, these differences do not have a
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// significant impact on driver performance. The implementation favors security
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// compliance and readability over hardware-specific tuning.
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package binaryutil
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