src/dawn/common/ityp_span.h

// Copyright 2020 The Dawn & Tint Authors
//
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// 1. Redistributions of source code must retain the above copyright notice, this
//    list of conditions and the following disclaimer.
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//    this list of conditions and the following disclaimer in the documentation
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#ifndef SRC_DAWN_COMMON_ITYP_SPAN_H_
#define SRC_DAWN_COMMON_ITYP_SPAN_H_

#include <type_traits>

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

namespace dawn::ityp {

// ityp::span is a helper class that wraps an unowned packed array of type |Value|.
// It stores the size and pointer to first element. It has the restriction that
// indices must be a particular type |Index|. This provides a type-safe way to index
// raw pointers.
template <typename Index, typename Value>
class span {
    using I = UnderlyingType<Index>;

  public:
    constexpr span() : mData(nullptr), mSize(0) {}
    constexpr span(Value* data, Index size) : mData(data), mSize(size) {}

    constexpr Value& operator[](Index i) const {
        DAWN_ASSERT(i < mSize);
        return mData[static_cast<I>(i)];
    }

    Value* data() noexcept { return mData; }

    const Value* data() const noexcept { return mData; }

    Value* begin() noexcept { return mData; }

    const Value* begin() const noexcept { return mData; }

    Value* end() noexcept { return mData + static_cast<I>(mSize); }

    const Value* end() const noexcept { return mData + static_cast<I>(mSize); }

    Value& front() {
        DAWN_ASSERT(mData != nullptr);
        DAWN_ASSERT(static_cast<I>(mSize) >= 0);
        return *mData;
    }

    const Value& front() const {
        DAWN_ASSERT(mData != nullptr);
        DAWN_ASSERT(static_cast<I>(mSize) >= 0);
        return *mData;
    }

    Value& back() {
        DAWN_ASSERT(mData != nullptr);
        DAWN_ASSERT(static_cast<I>(mSize) >= 0);
        return *(mData + static_cast<I>(mSize) - 1);
    }

    const Value& back() const {
        DAWN_ASSERT(mData != nullptr);
        DAWN_ASSERT(static_cast<I>(mSize) >= 0);
        return *(mData + static_cast<I>(mSize) - 1);
    }

    Index size() const { return mSize; }

  private:
    Value* mData;
    Index mSize;
};

// 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, Index{static_cast<UnderlyingType<Index>>(size)}};
}

}  // namespace dawn::ityp

#endif  // SRC_DAWN_COMMON_ITYP_SPAN_H_