chromium/third_party/pdfium/core/fxcrt/zip.h

// Copyright 2024 The PDFium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CORE_FXCRT_ZIP_H_
#define CORE_FXCRT_ZIP_H_

#include <stdint.h>

#include <tuple>
#include <utility>

#include "core/fxcrt/check_op.h"
#include "core/fxcrt/compiler_specific.h"
#include "core/fxcrt/span.h"

namespace fxcrt {

// Vastly simplified implementation of ideas from C++23 zip_view<>. Allows
// safe traversal of two or three ranges with a single bounds check per
// iteration.

// Example two range usage:
//   struct RGB { uint8_t r; uint8_t g; uint8_t b; };
//   const uint8_t gray[256] = { ... };
//   RGB rgbs[260];
//   for (auto [in, out] : Zip(gray, rgbs)) {
//     out.r = in;
//     out.g = in;
//     out.b = in;
//   }
// which fills the first 256 elements of rgbs with the corresponding gray
// value in each component, say.

// Differences include:
// - Only zips together two or three views instead of N.
// - Size is determined by the first view, which must be smaller than the
//   other view(s).
// - With two views, the first view is presumed to be "input-like" and is const,
//   second view is presumed to be "output-like" and is non-const.
// - With three views, the first two views are presumed to be "input-like" and
//   are const.
// - Only those methods required to support use in a range-based for-loop
//   are provided.

template <typename T, typename U>
class ZipView2 { … };

// Same as `ZipView2`, but with 2 inputs and 1 output.
template <typename T, typename U, typename V>
class ZipView3 { … };

template <typename T, typename U>
auto Zip(const T& first, U&& second) { … }

template <typename T, typename U, typename V>
auto Zip(const T& first, const U& second, V&& third) { … }

}  // namespace fxcrt

#endif  // CORE_FXCRT_ZIP_H_