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ef8825bfe6
LLVM has removed llvm::Optional, move over to std::optional. Also clang-format to fix up all the renamed #includes.
83 lines
2.4 KiB
C++
83 lines
2.4 KiB
C++
//===--- BitPatternReader.h - Split bit patterns into chunks. -------------===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2019 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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#pragma once
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#include "swift/Basic/ClusteredBitVector.h"
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#include "llvm/ADT/APInt.h"
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#include <optional>
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namespace swift {
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namespace irgen {
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/// BitPatternReader allows an APInt to be read from in chunks.
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/// Chunks may be read starting from either the least significant bit
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/// (little-endian) or the most significant bit (big-endian).
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///
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/// This is useful when interpreting an APInt as a multi-byte mask
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/// that needs to be applied to a value with a composite type.
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///
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/// Example:
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///
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/// // big-endian
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/// auto x = BitPatternReader(APInt(32, 0x1234), false);
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/// x.read(16) // 0x12
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/// x.read(8) // 0x3
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/// x.read(8) // 0x4
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///
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/// // little-endian
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/// auto y = BitPatternReader(APInt(32, 0x1234), true);
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/// y.read(16) // 0x34
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/// y.read(8) // 0x2
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/// y.read(8) // 0x1
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///
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class BitPatternReader {
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using APInt = llvm::APInt;
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const APInt Value;
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const bool LittleEndian;
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unsigned Offset = 0;
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public:
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/// If the reader is in little-endian mode then bits will be read
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/// from the least significant to the most significant. Otherwise
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/// they will be read from the most significant to the least
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/// significant.
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BitPatternReader(const APInt &value, bool littleEndian) :
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Value(value),
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LittleEndian(littleEndian) {}
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/// Read the given number of bits from the unread part of the
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/// underlying value and adjust the remaining value as appropriate.
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APInt read(unsigned numBits) {
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assert(numBits % 8 == 0);
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assert(Value.getBitWidth() >= Offset + numBits);
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unsigned offset = Offset;
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if (!LittleEndian) {
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offset = Value.getBitWidth() - offset - numBits;
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}
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Offset += numBits;
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return Value.extractBits(numBits, offset);
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}
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// Skip the number of bits provided.
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void skip(unsigned numBits) {
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assert(numBits % 8 == 0);
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assert(Value.getBitWidth() >= Offset + numBits);
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Offset += numBits;
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}
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};
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} // end namespace irgen
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} // end namespace swift
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