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diff --git a/lib/jxl/inverse_mtf-inl.h b/lib/jxl/inverse_mtf-inl.h
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+++ b/lib/jxl/inverse_mtf-inl.h
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+// Copyright (c) the JPEG XL Project Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// SIMDified inverse-move-to-front transform.
+
+#if defined(LIB_JXL_INVERSE_MTF_INL_H_) == defined(HWY_TARGET_TOGGLE)
+#ifdef LIB_JXL_INVERSE_MTF_INL_H_
+#undef LIB_JXL_INVERSE_MTF_INL_H_
+#else
+#define LIB_JXL_INVERSE_MTF_INL_H_
+#endif
+
+#include <hwy/highway.h>
+
+#include "lib/jxl/sanitizers.h"
+
+HWY_BEFORE_NAMESPACE();
+namespace jxl {
+namespace HWY_NAMESPACE {
+
+// These templates are not found via ADL.
+using hwy::HWY_NAMESPACE::FirstN;
+using hwy::HWY_NAMESPACE::IfThenElse;
+using hwy::HWY_NAMESPACE::Load;
+using hwy::HWY_NAMESPACE::LoadU;
+using hwy::HWY_NAMESPACE::StoreU;
+
+inline void MoveToFront(uint8_t* v, uint8_t index) {
+  uint8_t value = v[index];
+  uint8_t i = index;
+  if (i < 4) {
+    for (; i; --i) v[i] = v[i - 1];
+  } else {
+    const HWY_CAPPED(uint8_t, 64) d;
+    int tail = i & (Lanes(d) - 1);
+    if (tail) {
+      i -= tail;
+      const auto vec = Load(d, v + i);
+      const auto prev = LoadU(d, v + i + 1);
+      StoreU(IfThenElse(FirstN(d, tail), vec, prev), d, v + i + 1);
+    }
+    while (i) {
+      i -= Lanes(d);
+      const auto vec = Load(d, v + i);
+      StoreU(vec, d, v + i + 1);
+    }
+  }
+  v[0] = value;
+}
+
+inline void InverseMoveToFrontTransform(uint8_t* v, int v_len) {
+  HWY_ALIGN uint8_t mtf[256 + 64];
+  int i;
+  for (i = 0; i < 256; ++i) {
+    mtf[i] = static_cast<uint8_t>(i);
+  }
+#if JXL_MEMORY_SANITIZER
+  const HWY_CAPPED(uint8_t, 64) d;
+  for (size_t j = 0; j < Lanes(d); ++j) {
+    mtf[256 + j] = 0;
+  }
+#endif  // JXL_MEMORY_SANITIZER
+  for (i = 0; i < v_len; ++i) {
+    uint8_t index = v[i];
+    v[i] = mtf[index];
+    if (index) MoveToFront(mtf, index);
+  }
+}
+
+// NOLINTNEXTLINE(google-readability-namespace-comments)
+}  // namespace HWY_NAMESPACE
+}  // namespace jxl
+HWY_AFTER_NAMESPACE();
+
+#endif  // LIB_JXL_INVERSE_MTF_INL_H_
+
+#if HWY_ONCE
+#ifndef INVERSE_MTF_ONCE
+#define INVERSE_MTF_ONCE
+
+namespace jxl {
+inline void InverseMoveToFrontTransform(uint8_t* v, int v_len) {
+  return HWY_STATIC_DISPATCH(InverseMoveToFrontTransform)(v, v_len);
+}
+}  // namespace jxl
+
+#endif  // INVERSE_MTF_ONCE
+#endif  // HWY_ONCE