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ca402f19b1
Previously, they would forward their unused spare bits to be used by other multi-payload enums, but did not implement anything for single-payload extra inhabitants.
54 lines
1.7 KiB
C++
54 lines
1.7 KiB
C++
//===--- Enum.h - Enum implementation runtime declarations ------*- C++ -*-===//
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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) 2014 - 2017 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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//
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// Enum implementation details declarations relevant to the ABI.
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//
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//===----------------------------------------------------------------------===//
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#ifndef SWIFT_ABI_ENUM_H
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#define SWIFT_ABI_ENUM_H
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#include <stdlib.h>
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namespace swift {
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struct EnumTagCounts {
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unsigned numTags, numTagBytes;
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};
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inline EnumTagCounts
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getEnumTagCounts(size_t size, unsigned emptyCases, unsigned payloadCases) {
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// We can use the payload area with a tag bit set somewhere outside of the
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// payload area to represent cases. See how many bytes we need to cover
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// all the empty cases.
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unsigned numTags = payloadCases;
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if (emptyCases > 0) {
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if (size >= 4)
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// Assume that one tag bit is enough if the precise calculation overflows
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// an int32.
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numTags += 1;
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else {
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unsigned bits = size * 8U;
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unsigned casesPerTagBitValue = 1U << bits;
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numTags += ((emptyCases + (casesPerTagBitValue-1U)) >> bits);
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}
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}
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unsigned numTagBytes = (numTags <= 1 ? 0 :
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numTags < 256 ? 1 :
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numTags < 65536 ? 2 : 4);
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return {numTags, numTagBytes};
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}
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} // namespace swift
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#endif // SWIFT_ABI_ENUM_H
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