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diff --git a/third_party/jpeg-xl/lib/jxl/enc_fast_lossless.h b/third_party/jpeg-xl/lib/jxl/enc_fast_lossless.h
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+++ b/third_party/jpeg-xl/lib/jxl/enc_fast_lossless.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.
+
+#ifndef LIB_JXL_ENC_FAST_LOSSLESS_H_
+#define LIB_JXL_ENC_FAST_LOSSLESS_H_
+#include <stdlib.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Simple encoding API.
+
+// A FJxlParallelRunner must call fun(opaque, i) for all i from 0 to count. It
+// may do so in parallel.
+typedef void(FJxlParallelRunner)(void* runner_opaque, void* opaque,
+                                 void fun(void*, size_t), size_t count);
+
+// You may pass `nullptr` as a runner: encoding will be sequential.
+size_t JxlFastLosslessEncode(const unsigned char* rgba, size_t width,
+                             size_t row_stride, size_t height, size_t nb_chans,
+                             size_t bitdepth, int big_endian, int effort,
+                             unsigned char** output, void* runner_opaque,
+                             FJxlParallelRunner runner);
+
+// More complex API for cases in which you may want to allocate your own buffer
+// and other advanced use cases.
+
+// Opaque struct that represents an intermediate state of the computation.
+struct JxlFastLosslessFrameState;
+
+// Returned JxlFastLosslessFrameState must be freed by calling
+// JxlFastLosslessFreeFrameState.
+JxlFastLosslessFrameState* JxlFastLosslessPrepareFrame(
+    const unsigned char* rgba, size_t width, size_t row_stride, size_t height,
+    size_t nb_chans, size_t bitdepth, int big_endian, int effort,
+    void* runner_opaque, FJxlParallelRunner runner);
+
+// Prepare the (image/frame) header. You may encode animations by concatenating
+// the output of multiple frames, of which the first one has add_image_header =
+// 1 and subsequent ones have add_image_header = 0, and all frames but the last
+// one have is_last = 0.
+void JxlFastLosslessPrepareHeader(JxlFastLosslessFrameState* frame,
+                                  int add_image_header, int is_last);
+
+// Upper bound on the required output size, including any padding that may be
+// required by JxlFastLosslessWriteOutput. Cannot be called before
+// JxlFastLosslessPrepareHeader.
+size_t JxlFastLosslessMaxRequiredOutput(const JxlFastLosslessFrameState* frame);
+
+// Actual size of the frame once it is encoded. This is not identical to
+// JxlFastLosslessMaxRequiredOutput because JxlFastLosslessWriteOutput may
+// require extra padding.
+size_t JxlFastLosslessOutputSize(const JxlFastLosslessFrameState* frame);
+
+// Writes the frame to the given output buffer. Returns the number of bytes that
+// were written, which is at least 1 unless the entire output has been written
+// already. It is required that `output_size >= 32` when calling this function.
+// This function must be called repeatedly until it returns 0.
+size_t JxlFastLosslessWriteOutput(JxlFastLosslessFrameState* frame,
+                                  unsigned char* output, size_t output_size);
+
+// Frees the provided frame state.
+void JxlFastLosslessFreeFrameState(JxlFastLosslessFrameState* frame);
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // LIB_JXL_ENC_FAST_LOSSLESS_H_