src/dawn/common/ityp_span.h

// Copyright 2020 The Dawn & Tint Authors
//
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// modification, are permitted provided that the following conditions are met:
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//    this list of conditions and the following disclaimer in the documentation
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#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/439062058): Remove this and convert code to safer constructs.
#pragma allow_unsafe_buffers
#endif

#ifndef SRC_DAWN_COMMON_ITYP_SPAN_H_
#define SRC_DAWN_COMMON_ITYP_SPAN_H_

#include <cstddef>
#include <limits>
#include <span>

#include "dawn/common/Numeric.h"
#include "dawn/common/UnderlyingType.h"

namespace dawn::ityp {

// ityp::span is a helper class that wraps std::span<T, std::dynamic_extent>
// with the restriction that indices must be a particular type |Index|.
template <typename Index, typename Value>
class span : private ::std::span<Value> {
    using I = UnderlyingType<Index>;
    using Base = ::std::span<Value>;

    static_assert(UnsignedUnderlyingType<Index>, "Index type must be unsigned");

  public:
    constexpr span() = default;
    constexpr span(Value* data, Index size) : Base{data, checked_cast<size_t>(size)} {}

    using Base::begin, Base::end;
    using Base::front, Base::back;

    using Base::data;

    constexpr Value& operator[](Index i) const { return Base::operator[](checked_cast<size_t>(i)); }

    constexpr Index size() const { return Index(static_cast<I>(Base::size())); }
};

// ityp::SpanFromUntyped<Index>(myValues, myValueCount) creates a span<Index, Value> from a C-style
// span that's without a TypedInteger index. It is useful at the interface between code that doesn't
// use ityp and code that does.
template <typename Index, typename Value>
span<Index, Value> SpanFromUntyped(Value* data, size_t size) {
    return {data, checked_cast<Index>(size)};
}

}  // namespace dawn::ityp

#endif  // SRC_DAWN_COMMON_ITYP_SPAN_H_