// 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_QUANTIZER_H_

#define LIB_JXL_QUANTIZER_H_

#include <algorithm>

#include <cmath>

#include <cstddef>

#include <cstdint>

#include <cstdlib>

#include "lib/jxl/base/compiler_specific.h"

#include "lib/jxl/base/rect.h"

#include "lib/jxl/base/status.h"

#include "lib/jxl/dec_bit_reader.h"

#include "lib/jxl/field_encodings.h"

#include "lib/jxl/fields.h"

#include "lib/jxl/image.h"

#include "lib/jxl/quant_weights.h"

// Quantizes DC and AC coefficients, with separate quantization tables according

// to the quant_kind (which is currently computed from the AC strategy and the

// block index inside that strategy).

namespace jxl {

enum class AcStrategyType : uint32_t;

static constexpr int kGlobalScaleDenom = 1 << 16;

static constexpr int kGlobalScaleNumerator = 4096;

// zero-biases for quantizing channels X, Y, B

static constexpr float kZeroBiasDefault[3] = {0.5f, 0.5f, 0.5f};

// Returns adjusted version of a quantized integer, such that its value is

// closer to the expected value of the original.

// The residuals of AC coefficients that we quantize are not uniformly

// distributed. Numerical experiments show that they have a distribution with

// the "shape" of 1/(1+x^2) [up to some coefficients]. This means that the

// expected value of a coefficient that gets quantized to x will not be x

// itself, but (at least with reasonable approximation):

// - 0 if x is 0

// - x * biases[c] if x is 1 or -1

// - x - biases[3]/x otherwise

// This follows from computing the distribution of the quantization bias, which

// can be approximated fairly well by <constant>/x when |x| is at least two.

static constexpr float kBiasNumerator = 0.145f;

static constexpr float kDefaultQuantBias[4] = {

    1.0f - 0.05465007330715401f,

    1.0f - 0.07005449891748593f,

    1.0f - 0.049935103337343655f,

    0.145f,

};

struct QuantizerParams;

class Quantizer {

 public:

  explicit Quantizer(const DequantMatrices& dequant);

  Quantizer(const DequantMatrices& dequant, int quant_dc, int global_scale);

  static constexpr int32_t kQuantMax = 256;

  static JXL_INLINE int32_t ClampVal(float val) {

    return static_cast<int32_t>(

        std::max(1.0f, std::min<float>(val, kQuantMax)));

  }

  float ScaleGlobalScale(const float scale) {

    int new_global_scale = static_cast<int>(std::lround(global_scale_ * scale));

    float scale_out = new_global_scale * 1.0f / global_scale_;

    global_scale_ = new_global_scale;

    RecomputeFromGlobalScale();

    return scale_out;

  }

  // Recomputes other derived fields after global_scale_ has changed.

  void RecomputeFromGlobalScale() {

    global_scale_float_ = global_scale_ * (1.0 / kGlobalScaleDenom);

    inv_global_scale_ = 1.0 * kGlobalScaleDenom / global_scale_;

    inv_quant_dc_ = inv_global_scale_ / quant_dc_;

    for (size_t c = 0; c < 3; c++) {

      mul_dc_[c] = GetDcStep(c);

      inv_mul_dc_[c] = GetInvDcStep(c);

    }

  }

  // Returns scaling factor such that Scale() * (RawDC() or RawQuantField())

  // pixels yields the same float values returned by GetQuantField.

  JXL_INLINE float Scale() const { return global_scale_float_; }

  // Reciprocal of Scale().

  JXL_INLINE float InvGlobalScale() const { return inv_global_scale_; }

  void SetQuantFieldRect(const ImageF& qf, const Rect& rect,

                         ImageI* JXL_RESTRICT raw_quant_field) const;

  Status SetQuantField(float quant_dc, const ImageF& qf,

                       ImageI* JXL_RESTRICT raw_quant_field);

  void SetQuant(float quant_dc, float quant_ac,

                ImageI* JXL_RESTRICT raw_quant_field);

  // Returns the DC quantization base value, which is currently global (not

  // adaptive). The actual scale factor used to dequantize pixels in channel c

  // is: inv_quant_dc() * dequant_->DCQuant(c).

  float inv_quant_dc() const { return inv_quant_dc_; }

  // Dequantize by multiplying with this times dequant_matrix.

  float inv_quant_ac(int32_t quant) const { return inv_global_scale_ / quant; }

  QuantizerParams GetParams() const;

  Status Decode(BitReader* reader);

  void DumpQuantizationMap(const ImageI& raw_quant_field) const;

  JXL_INLINE const float* DequantMatrix(AcStrategyType quant_kind,

                                        size_t c) const {

    return dequant_->Matrix(quant_kind, c);

  }

  JXL_INLINE const float* InvDequantMatrix(AcStrategyType quant_kind,

                                           size_t c) const {

    return dequant_->InvMatrix(quant_kind, c);

  }

  // Calculates DC quantization step.

  JXL_INLINE float GetDcStep(size_t c) const {

    return inv_quant_dc_ * dequant_->DCQuant(c);

  }

  JXL_INLINE float GetInvDcStep(size_t c) const {

    return dequant_->InvDCQuant(c) * (global_scale_float_ * quant_dc_);

  }

  JXL_INLINE const float* MulDC() const { return mul_dc_; }

  JXL_INLINE const float* InvMulDC() const { return inv_mul_dc_; }

  JXL_INLINE void ClearDCMul() {

    std::fill(mul_dc_, mul_dc_ + 4, 1.f);

    std::fill(inv_mul_dc_, inv_mul_dc_ + 4, 1.f);

  }

  void ComputeGlobalScaleAndQuant(float quant_dc, float quant_median,

                                  float quant_median_absd);

 private:

  float mul_dc_[4];

  float inv_mul_dc_[4];

  // These are serialized:

  int global_scale_;

  int quant_dc_;

  // These are derived from global_scale_:

  float inv_global_scale_;

  float global_scale_float_;  // reciprocal of inv_global_scale_

  float inv_quant_dc_;

  float zero_bias_[3];

  const DequantMatrices* dequant_;

};

struct QuantizerParams : public Fields {

  QuantizerParams() { Bundle::Init(this); }

  JXL_FIELDS_NAME(QuantizerParams)

  Status VisitFields(Visitor* JXL_RESTRICT visitor) override;

  uint32_t global_scale;

  uint32_t quant_dc;

};

}  // namespace jxl

#endif  // LIB_JXL_QUANTIZER_H_