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diff --git a/extern/ceres/internal/ceres/pair_hash.h b/extern/ceres/internal/ceres/pair_hash.h
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+++ b/extern/ceres/internal/ceres/pair_hash.h
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+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2018 Google Inc. All rights reserved.
+// http://ceres-solver.org/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: keir@google.com (Keir Mierle)
+//
+// A hasher for std::pair<T, T>.
+
+#ifndef CERES_INTERNAL_PAIR_HASH_H_
+#define CERES_INTERNAL_PAIR_HASH_H_
+
+#include "ceres/internal/port.h"
+#include <cstdint>
+#include <utility>
+
+namespace ceres {
+namespace internal {
+
+#if defined(_WIN32) && !defined(__MINGW64__) && !defined(__MINGW32__)
+#define GG_LONGLONG(x) x##I64
+#define GG_ULONGLONG(x) x##UI64
+#else
+#define GG_LONGLONG(x) x##LL
+#define GG_ULONGLONG(x) x##ULL
+#endif
+
+// The hash function is due to Bob Jenkins (see
+// http://burtleburtle.net/bob/hash/index.html). Each mix takes 36 instructions,
+// in 18 cycles if you're lucky. On x86 architectures, this requires 45
+// instructions in 27 cycles, if you're lucky.
+//
+// 32bit version
+inline void hash_mix(uint32_t& a, uint32_t& b, uint32_t& c) {
+  a -= b; a -= c; a ^= (c>>13);
+  b -= c; b -= a; b ^= (a<<8);
+  c -= a; c -= b; c ^= (b>>13);
+  a -= b; a -= c; a ^= (c>>12);
+  b -= c; b -= a; b ^= (a<<16);
+  c -= a; c -= b; c ^= (b>>5);
+  a -= b; a -= c; a ^= (c>>3);
+  b -= c; b -= a; b ^= (a<<10);
+  c -= a; c -= b; c ^= (b>>15);
+}
+
+// 64bit version
+inline void hash_mix(uint64_t& a, uint64_t& b, uint64_t& c) {
+  a -= b; a -= c; a ^= (c>>43);
+  b -= c; b -= a; b ^= (a<<9);
+  c -= a; c -= b; c ^= (b>>8);
+  a -= b; a -= c; a ^= (c>>38);
+  b -= c; b -= a; b ^= (a<<23);
+  c -= a; c -= b; c ^= (b>>5);
+  a -= b; a -= c; a ^= (c>>35);
+  b -= c; b -= a; b ^= (a<<49);
+  c -= a; c -= b; c ^= (b>>11);
+}
+
+inline uint32_t Hash32NumWithSeed(uint32_t num, uint32_t c) {
+  // The golden ratio; an arbitrary value.
+  uint32_t b = 0x9e3779b9UL;
+  hash_mix(num, b, c);
+  return c;
+}
+
+inline uint64_t Hash64NumWithSeed(uint64_t num, uint64_t c) {
+  // More of the golden ratio.
+  uint64_t b = GG_ULONGLONG(0xe08c1d668b756f82);
+  hash_mix(num, b, c);
+  return c;
+}
+
+// Hasher for STL pairs. Requires hashers for both members to be defined.
+struct pair_hash {
+ public:
+  template <typename T>
+  std::size_t operator()(const std::pair<T, T>& p) const {
+    const std::size_t h1 = std::hash<T>()(p.first);
+    const std::size_t h2 = std::hash<T>()(p.second);
+    // The decision below is at compile time
+    return (sizeof(h1) <= sizeof(uint32_t)) ? Hash32NumWithSeed(h1, h2)
+                                            : Hash64NumWithSeed(h1, h2);
+  }
+};
+
+}  // namespace internal
+}  // namespace ceres
+
+#endif  // CERES_INTERNAL_PAIR_HASH_H_