internal/pack_neon.h - platform/external/gemmlowp - Git at Google

 // Copyright 2015 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 // pack_neon.h: optimized NEON specializations of the templates in pack.h.

 #ifndef GEMMLOWP_INTERNAL_PACK_NEON_H_
 #define GEMMLOWP_INTERNAL_PACK_NEON_H_

 #include "pack.h"

 #include <arm_neon.h>

 namespace gemmlowp {

 // Variant of PseudoRandomNonzeroBytesGenerator that produces
 // random NEON 128-bit vectors.
 class NEONPseudoRandomNonzeroBytesGenerator {
  public:
   NEONPseudoRandomNonzeroBytesGenerator() {
     uint8_t s = 1;
     std::uint8_t a[16];
     for (int i = 0; i < 16; i++) {
       a[i] = s;
       // Xorshift8(7,7,1). Very important to choose a different
       // xorshift than we do in get(), otherwise lanes would contain
       // the same values!
       s ^= s << 7;
       s ^= s >> 7;
       s ^= s << 1;
     }
     x_ = vld1q_u8(a);
   }

   uint8x16_t get() {
     // Xorshift8(7,5,3)
     x_ = veorq_u8(x_, vshlq_n_u8(x_, 7));
     x_ = veorq_u8(x_, vshrq_n_u8(x_, 5));
     x_ = veorq_u8(x_, vshlq_n_u8(x_, 3));
     return x_;
   }

  private:
   // State
   uint8x16_t x_;
 };

 // Requantizes source uint8 values in [0..255] range
 // to the range specified by BitDepth, [0..((2^bits)-1)].
 // Bias must be avoided. Currently this is achieved
 // by probabilistic rounding.
 template <typename BitDepth, RoundingMode Rounding>
 uint8x16_t Requantize(uint8x16_t raw_src_data,
                       NEONPseudoRandomNonzeroBytesGenerator* prng) {
   static const int kBits = BitDepth::kBits;
   static const std::uint8_t kMaxVal = (1 << kBits) - 1;

   if (kBits == 8) {
     return raw_src_data;
   }

   // We will need to temporarily work in 16 bit precision.
   uint16x8_t x[2];

   // Multiply source values by 2^kBits.
   x[0] = vshll_n_u8(vget_low_u8(raw_src_data), kBits);
   x[1] = vshll_n_u8(vget_high_u8(raw_src_data), kBits);

   // Subtract source values, so we effectively have them
   // multiplied by (2^kBits) - 1.
   x[0] = vsubw_u8(x[0], vget_low_u8(raw_src_data));
   x[1] = vsubw_u8(x[1], vget_high_u8(raw_src_data));

   // Compute the rounding offset.
   uint8x16_t rounding_offset;
   switch (Rounding) {
     case RoundingMode::Nearest:
       // 128 is the midpoint in [1..255], and [1..255] is the interval
       // that we use for offsets here, see the comment below on
       // the Probabilistic case.
       rounding_offset = vdupq_n_u8(128);
       break;
     case RoundingMode::Probabilistic:
       // Take nonzero bytes in [1..255].
       // In principle we want a value in [0..254], but:
       //   1) Below we will be multiplying by 257/256 instead of 256/255,
       //      which is slightly too low, and this helps compensate for that.
       //      (One checks this on paper and this also gives better results
       //      on TestWithRealData).
       //   1 bis) Note also that this 257/256 != 256/255 helps ensure
       //      that no overflow can happen, even with offset=255.
       //   2) Our PRNG, xorshift, inherently wants to generate values
       //      in [1..255] so this saves a couple of instructions.
       rounding_offset = prng->get();
       break;
     default:
       assert(false);
       rounding_offset = vdupq_n_u8(0);
   }

   // Add the rounding offset.
   x[0] = vaddw_u8(x[0], vget_low_u8(rounding_offset));
   x[1] = vaddw_u8(x[1], vget_high_u8(rounding_offset));

   // Multiply by 257/256, which is close enough to 256/255.
   x[0] = vaddq_u16(x[0], vshrq_n_u16(x[0], 8));
   x[1] = vaddq_u16(x[1], vshrq_n_u16(x[1], 8));

   uint8x8_t y[2];
   // Divide again by 256.
   y[0] = vshrn_n_u16(x[0], 8);
   y[1] = vshrn_n_u16(x[1], 8);

   return vcombine_u8(y[0], y[1]);
 }

 typedef SideMap<const std::uint8_t, SideMapOrder::WidthMajor>
     WidthMajorUint8SideMap;

 template <int Cells>
 using DepthMajorSideFormatNCells4x2 = KernelSideFormat<CellFormat<4, 2>, Cells>;

 template <int Cells>
 class PackingRegisterBlock<
     WidthMajorUint8SideMap,
     PackedSideBlock<DepthMajorSideFormatNCells4x2<Cells> > >
     : public PackingRegisterBlockBase<
           WidthMajorUint8SideMap,
           PackedSideBlock<DepthMajorSideFormatNCells4x2<Cells> > > {
  public:
   typedef DepthMajorSideFormatNCells4x2<Cells> KernelSideFormat;
   typedef typename KernelSideFormat::Cell CellFormat;
   static const int kCells = KernelSideFormat::kCells;
   static const int kCellWidth = CellFormat::kWidth;
   static const int kKernelWidth = CellFormat::kWidth * kCells;
   static const int kCellDepth = CellFormat::kDepth;
   static const int kCellSize = CellFormat::kSize;

   typedef NEONPseudoRandomNonzeroBytesGenerator
       PseudoRandomNonzeroBytesGenerator;

   template <typename BitDepth, RoundingMode Rounding>
   void Pack(PackedSideBlock<KernelSideFormat>* dst, int start_width,
             PseudoRandomNonzeroBytesGenerator* prng) {
     static const int kBits = BitDepth::kBits;
     static const std::uint16_t kMaxVal = (1 << kBits) - 1;
     std::uint8_t* dst_ptr = dst->current_data();
     const std::uint8_t* const src_ptr = this->complete_src_.data();
     const int stride = this->complete_src_.stride();
     // Load and requantize source WidthMajor data
     uint8x16_t src_lines[4 * kCells];
     for (int i = 0; i < 4 * kCells; i++) {
       src_lines[i] = Requantize<BitDepth, Rounding>(
         vld1q_u8(src_ptr + i * stride), prng);
     }
     // Reorder the data within registers to make DepthMajor 4x2 cells
     uint8x16x2_t src_lines_intertwined_2x[2 * kCells];
     for (int i = 0; i < kCells; i++) {
       src_lines_intertwined_2x[2 * i] =
           vzipq_u8(src_lines[4 * i], src_lines[4 * i + 2]);
       src_lines_intertwined_2x[2 * i + 1] =
           vzipq_u8(src_lines[4 * i + 1], src_lines[4 * i + 3]);
     }
     uint8x16x2_t src_lines_intertwined_4x[2 * kCells];
     for (int i = 0; i < kCells; i++) {
       src_lines_intertwined_4x[2 * i] =
           vzipq_u8(src_lines_intertwined_2x[2 * i].val[0],
                    src_lines_intertwined_2x[2 * i + 1].val[0]);
       src_lines_intertwined_4x[2 * i + 1] =
           vzipq_u8(src_lines_intertwined_2x[2 * i].val[1],
                    src_lines_intertwined_2x[2 * i + 1].val[1]);
     }
     // Store the resulting DepthMajor 4x2 cells in the destination packed block
     for (int outer = 0; outer < 2; outer++) {
       for (int inner = 0; inner < 2; inner++) {
         for (int cell = 0; cell < kCells; cell++) {
           uint8x8_t value = vget_low_u8(
               src_lines_intertwined_4x[2 * cell + outer].val[inner]);
           vst1_u8(dst_ptr, value);
           dst_ptr += 8;
         }
         for (int cell = 0; cell < kCells; cell++) {
           uint8x8_t value = vget_high_u8(
               src_lines_intertwined_4x[2 * cell + outer].val[inner]);
           vst1_u8(dst_ptr, value);
           dst_ptr += 8;
         }
       }
     }
     // Compute sums across the depth dimension
     uint16x8_t sums_of_2_cells[kCells][4];
     for (int outer = 0; outer < 2; outer++) {
       for (int inner = 0; inner < 2; inner++) {
         int i = 2 * outer + inner;
         for (int cell = 0; cell < kCells; cell++) {
           sums_of_2_cells[cell][i] = vaddl_u8(
               vget_low_u8(
                   src_lines_intertwined_4x[2 * cell + outer].val[inner]),
               vget_high_u8(
                   src_lines_intertwined_4x[2 * cell + outer].val[inner]));
         }
       }
     }
     int32x4_t sums_of_4_cells[kCells][4];
     for (int i = 0; i < 4; i++) {
       for (int cell = 0; cell < kCells; cell++) {
         sums_of_4_cells[cell][i] = vreinterpretq_s32_u32(
             vaddl_u16(vget_low_u16(sums_of_2_cells[cell][i]),
                       vget_high_u16(sums_of_2_cells[cell][i])));
       }
     }
     // Update the rank_one_update vector
     for (int cell = 0; cell < kCells; cell++) {
       int32x4_t s01 =
           vaddq_s32(sums_of_4_cells[cell][0], sums_of_4_cells[cell][1]);
       int32x4_t s23 =
           vaddq_s32(sums_of_4_cells[cell][2], sums_of_4_cells[cell][3]);
       int32x4_t s = vaddq_s32(s01, s23);
       int32x4_t u = vmulq_n_s32(s, dst->rank_one_update_multiplier());
       std::int32_t* rank_one_update_ptr =
           dst->rank_one_update() + start_width + 4 * cell;
       vst1q_s32(rank_one_update_ptr,
                 vaddq_s32(u, vld1q_s32(rank_one_update_ptr)));
     }
     dst->seek_forward_n_cells(kCells * kRegisterSize / kCellDepth);
   }
 };

 template <int Cells>
 using WidthMajorSideFormatNCells4x2 =
     KernelSideFormat<CellFormat<4, 2, CellOrder::WidthMajor>, Cells>;

 template <int Cells>
 class PackingRegisterBlock<
     WidthMajorUint8SideMap,
     PackedSideBlock<WidthMajorSideFormatNCells4x2<Cells> > >
     : public PackingRegisterBlockBase<
           WidthMajorUint8SideMap,
           PackedSideBlock<WidthMajorSideFormatNCells4x2<Cells> > > {
  public:
   typedef WidthMajorSideFormatNCells4x2<Cells> KernelSideFormat;
   typedef typename KernelSideFormat::Cell CellFormat;
   static const int kCells = KernelSideFormat::kCells;
   static const int kCellWidth = CellFormat::kWidth;
   static const int kKernelWidth = CellFormat::kWidth * kCells;
   static const int kCellDepth = CellFormat::kDepth;
   static const int kCellSize = CellFormat::kSize;

   typedef NEONPseudoRandomNonzeroBytesGenerator
       PseudoRandomNonzeroBytesGenerator;

   template <typename BitDepth, RoundingMode Rounding>
   void Pack(PackedSideBlock<KernelSideFormat>* dst, int start_width,
             PseudoRandomNonzeroBytesGenerator* prng) {
     static const int kBits = BitDepth::kBits;
     static const std::uint16_t kMaxVal = (1 << kBits) - 1;
     std::uint8_t* dst_ptr = dst->current_data();
     const std::uint8_t* src_ptr = this->complete_src_.data();
     const int stride = this->complete_src_.stride();
     // Load and requantize source WidthMajor data
     uint16x8_t src_lines[kCells * 4];
     for (int i = 0; i < kCells; i++) {
 // This packing path is used with our current
 // less-than-8-bit kernel, and the partial unrolling of this loop
 // results in substantially faster code (thanks to better
 // register allocation) on Nexus 5.

 #define GEMMLOWP_UNROLLED_LOOP_ITER(k)                     \
   src_lines[4 * i + k] =                                   \
       vreinterpretq_u16_u8(Requantize<BitDepth, Rounding>( \
         vld1q_u8(src_ptr), prng));                         \
   src_ptr += stride;

       GEMMLOWP_UNROLLED_LOOP_ITER(0)
       GEMMLOWP_UNROLLED_LOOP_ITER(1)
       GEMMLOWP_UNROLLED_LOOP_ITER(2)
       GEMMLOWP_UNROLLED_LOOP_ITER(3)

 #undef GEMMLOWP_UNROLLED_LOOP_ITER
     }
     // Reorder the data within registers to make WidthMajor 4x2 cells
     uint16x8x2_t src_lines_intertwined_2x[2 * kCells];
     for (int i = 0; i < kCells; i++) {
       src_lines_intertwined_2x[2 * i] =
           vzipq_u16(src_lines[4 * i], src_lines[4 * i + 2]);
       src_lines_intertwined_2x[2 * i + 1] =
           vzipq_u16(src_lines[4 * i + 1], src_lines[4 * i + 3]);
     }
     uint16x8x2_t src_lines_intertwined_4x[2 * kCells];
     for (int i = 0; i < kCells; i++) {
       src_lines_intertwined_4x[2 * i] =
           vzipq_u16(src_lines_intertwined_2x[2 * i].val[0],
                     src_lines_intertwined_2x[2 * i + 1].val[0]);
       src_lines_intertwined_4x[2 * i + 1] =
           vzipq_u16(src_lines_intertwined_2x[2 * i].val[1],
                     src_lines_intertwined_2x[2 * i + 1].val[1]);
     }
     // Store the resulting WidthMajor 4x2 cells in the destination packed block
     for (int outer = 0; outer < 2; outer++) {
       for (int inner = 0; inner < 2; inner++) {
         for (int cell = 0; cell < kCells; cell++) {
           uint8x8_t value = vreinterpret_u8_u16(vget_low_u16(
               src_lines_intertwined_4x[2 * cell + outer].val[inner]));
           vst1_u8(dst_ptr, value);
           dst_ptr += 8;
         }
         for (int cell = 0; cell < kCells; cell++) {
           uint8x8_t value = vreinterpret_u8_u16(vget_high_u16(
               src_lines_intertwined_4x[2 * cell + outer].val[inner]));
           vst1_u8(dst_ptr, value);
           dst_ptr += 8;
         }
       }
     }
     // Compute sums across the depth dimension
     uint16x8_t sums_of_2[kCells][4];
     for (int outer = 0; outer < 2; outer++) {
       for (int inner = 0; inner < 2; inner++) {
         int i = 2 * outer + inner;
         for (int cell = 0; cell < kCells; cell++) {
           sums_of_2[cell][i] = vpaddlq_u8(vreinterpretq_u8_u16(
               src_lines_intertwined_4x[2 * cell + outer].val[inner]));
         }
       }
     }
     uint16x8_t sums_of_4[kCells][2];
     for (int i = 0; i < 2; i++) {
       for (int cell = 0; cell < kCells; cell++) {
         sums_of_4[cell][i] =
             vaddq_u16(sums_of_2[cell][2 * i], sums_of_2[cell][2 * i + 1]);
       }
     }
     uint16x8_t sums_of_8[kCells];
     for (int cell = 0; cell < kCells; cell++) {
       sums_of_8[cell] = vaddq_u16(sums_of_4[cell][0], sums_of_4[cell][1]);
     }

     uint16x4_t sums_of_16[kCells];
     for (int cell = 0; cell < kCells; cell++) {
       sums_of_16[cell] = vadd_u16(vget_low_u16(sums_of_8[cell]),
                                   vget_high_u16(sums_of_8[cell]));
     }
     // Update the rank_one_update vector
     for (int cell = 0; cell < kCells; cell++) {
       int32x4_t s = vreinterpretq_s32_u32(vmovl_u16(sums_of_16[cell]));
       int32x4_t u = vmulq_n_s32(s, dst->rank_one_update_multiplier());
       std::int32_t* rank_one_update_ptr =
           dst->rank_one_update() + start_width + 4 * cell;
       vst1q_s32(rank_one_update_ptr,
                 vaddq_s32(u, vld1q_s32(rank_one_update_ptr)));
     }
     dst->seek_forward_n_cells(kCells * kRegisterSize / kCellDepth);
   }
 };

 }  // namespace gemmlowp

 #endif  // GEMMLOWP_INTERNAL_PACK_NEON_H_
	// Copyright 2015 Google Inc. All Rights Reserved.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	// pack_neon.h: optimized NEON specializations of the templates in pack.h.

	#ifndef GEMMLOWP_INTERNAL_PACK_NEON_H_
	#define GEMMLOWP_INTERNAL_PACK_NEON_H_

	#include "pack.h"

	#include <arm_neon.h>

	namespace gemmlowp {

	// Variant of PseudoRandomNonzeroBytesGenerator that produces
	// random NEON 128-bit vectors.
	class NEONPseudoRandomNonzeroBytesGenerator {
	public:
	NEONPseudoRandomNonzeroBytesGenerator() {
	uint8_t s = 1;
	std::uint8_t a[16];
	for (int i = 0; i < 16; i++) {
	a[i] = s;
	// Xorshift8(7,7,1). Very important to choose a different
	// xorshift than we do in get(), otherwise lanes would contain
	// the same values!
	s ^= s << 7;
	s ^= s >> 7;
	s ^= s << 1;
	}
	x_ = vld1q_u8(a);
	}

	uint8x16_t get() {
	// Xorshift8(7,5,3)
	x_ = veorq_u8(x_, vshlq_n_u8(x_, 7));
	x_ = veorq_u8(x_, vshrq_n_u8(x_, 5));
	x_ = veorq_u8(x_, vshlq_n_u8(x_, 3));
	return x_;
	}

	private:
	// State
	uint8x16_t x_;
	};

	// Requantizes source uint8 values in [0..255] range
	// to the range specified by BitDepth, [0..((2^bits)-1)].
	// Bias must be avoided. Currently this is achieved
	// by probabilistic rounding.
	template <typename BitDepth, RoundingMode Rounding>
	uint8x16_t Requantize(uint8x16_t raw_src_data,
	NEONPseudoRandomNonzeroBytesGenerator* prng) {
	static const int kBits = BitDepth::kBits;
	static const std::uint8_t kMaxVal = (1 << kBits) - 1;

	if (kBits == 8) {
	return raw_src_data;
	}

	// We will need to temporarily work in 16 bit precision.
	uint16x8_t x[2];

	// Multiply source values by 2^kBits.
	x[0] = vshll_n_u8(vget_low_u8(raw_src_data), kBits);
	x[1] = vshll_n_u8(vget_high_u8(raw_src_data), kBits);

	// Subtract source values, so we effectively have them
	// multiplied by (2^kBits) - 1.
	x[0] = vsubw_u8(x[0], vget_low_u8(raw_src_data));
	x[1] = vsubw_u8(x[1], vget_high_u8(raw_src_data));

	// Compute the rounding offset.
	uint8x16_t rounding_offset;
	switch (Rounding) {
	case RoundingMode::Nearest:
	// 128 is the midpoint in [1..255], and [1..255] is the interval
	// that we use for offsets here, see the comment below on
	// the Probabilistic case.
	rounding_offset = vdupq_n_u8(128);
	break;
	case RoundingMode::Probabilistic:
	// Take nonzero bytes in [1..255].
	// In principle we want a value in [0..254], but:
	// 1) Below we will be multiplying by 257/256 instead of 256/255,
	// which is slightly too low, and this helps compensate for that.
	// (One checks this on paper and this also gives better results
	// on TestWithRealData).
	// 1 bis) Note also that this 257/256 != 256/255 helps ensure
	// that no overflow can happen, even with offset=255.
	// 2) Our PRNG, xorshift, inherently wants to generate values
	// in [1..255] so this saves a couple of instructions.
	rounding_offset = prng->get();
	break;
	default:
	assert(false);
	rounding_offset = vdupq_n_u8(0);
	}

	// Add the rounding offset.
	x[0] = vaddw_u8(x[0], vget_low_u8(rounding_offset));
	x[1] = vaddw_u8(x[1], vget_high_u8(rounding_offset));

	// Multiply by 257/256, which is close enough to 256/255.
	x[0] = vaddq_u16(x[0], vshrq_n_u16(x[0], 8));
	x[1] = vaddq_u16(x[1], vshrq_n_u16(x[1], 8));

	uint8x8_t y[2];
	// Divide again by 256.
	y[0] = vshrn_n_u16(x[0], 8);
	y[1] = vshrn_n_u16(x[1], 8);

	return vcombine_u8(y[0], y[1]);
	}

	typedef SideMap<const std::uint8_t, SideMapOrder::WidthMajor>
	WidthMajorUint8SideMap;

	template <int Cells>
	using DepthMajorSideFormatNCells4x2 = KernelSideFormat<CellFormat<4, 2>, Cells>;

	template <int Cells>
	class PackingRegisterBlock<
	WidthMajorUint8SideMap,
	PackedSideBlock<DepthMajorSideFormatNCells4x2<Cells> > >
	: public PackingRegisterBlockBase<
	WidthMajorUint8SideMap,
	PackedSideBlock<DepthMajorSideFormatNCells4x2<Cells> > > {
	public:
	typedef DepthMajorSideFormatNCells4x2<Cells> KernelSideFormat;
	typedef typename KernelSideFormat::Cell CellFormat;
	static const int kCells = KernelSideFormat::kCells;
	static const int kCellWidth = CellFormat::kWidth;
	static const int kKernelWidth = CellFormat::kWidth * kCells;
	static const int kCellDepth = CellFormat::kDepth;
	static const int kCellSize = CellFormat::kSize;

	typedef NEONPseudoRandomNonzeroBytesGenerator
	PseudoRandomNonzeroBytesGenerator;

	template <typename BitDepth, RoundingMode Rounding>
	void Pack(PackedSideBlock<KernelSideFormat>* dst, int start_width,
	PseudoRandomNonzeroBytesGenerator* prng) {
	static const int kBits = BitDepth::kBits;
	static const std::uint16_t kMaxVal = (1 << kBits) - 1;
	std::uint8_t* dst_ptr = dst->current_data();
	const std::uint8_t* const src_ptr = this->complete_src_.data();
	const int stride = this->complete_src_.stride();
	// Load and requantize source WidthMajor data
	uint8x16_t src_lines[4 * kCells];
	for (int i = 0; i < 4 * kCells; i++) {
	src_lines[i] = Requantize<BitDepth, Rounding>(
	vld1q_u8(src_ptr + i * stride), prng);
	}
	// Reorder the data within registers to make DepthMajor 4x2 cells
	uint8x16x2_t src_lines_intertwined_2x[2 * kCells];
	for (int i = 0; i < kCells; i++) {
	src_lines_intertwined_2x[2 * i] =
	vzipq_u8(src_lines[4 * i], src_lines[4 * i + 2]);
	src_lines_intertwined_2x[2 * i + 1] =
	vzipq_u8(src_lines[4 * i + 1], src_lines[4 * i + 3]);
	}
	uint8x16x2_t src_lines_intertwined_4x[2 * kCells];
	for (int i = 0; i < kCells; i++) {
	src_lines_intertwined_4x[2 * i] =
	vzipq_u8(src_lines_intertwined_2x[2 * i].val[0],
	src_lines_intertwined_2x[2 * i + 1].val[0]);
	src_lines_intertwined_4x[2 * i + 1] =
	vzipq_u8(src_lines_intertwined_2x[2 * i].val[1],
	src_lines_intertwined_2x[2 * i + 1].val[1]);
	}
	// Store the resulting DepthMajor 4x2 cells in the destination packed block
	for (int outer = 0; outer < 2; outer++) {
	for (int inner = 0; inner < 2; inner++) {
	for (int cell = 0; cell < kCells; cell++) {
	uint8x8_t value = vget_low_u8(
	src_lines_intertwined_4x[2 * cell + outer].val[inner]);
	vst1_u8(dst_ptr, value);
	dst_ptr += 8;
	}
	for (int cell = 0; cell < kCells; cell++) {
	uint8x8_t value = vget_high_u8(
	src_lines_intertwined_4x[2 * cell + outer].val[inner]);
	vst1_u8(dst_ptr, value);
	dst_ptr += 8;
	}
	}
	}
	// Compute sums across the depth dimension
	uint16x8_t sums_of_2_cells[kCells][4];
	for (int outer = 0; outer < 2; outer++) {
	for (int inner = 0; inner < 2; inner++) {
	int i = 2 * outer + inner;
	for (int cell = 0; cell < kCells; cell++) {
	sums_of_2_cells[cell][i] = vaddl_u8(
	vget_low_u8(
	src_lines_intertwined_4x[2 * cell + outer].val[inner]),
	vget_high_u8(
	src_lines_intertwined_4x[2 * cell + outer].val[inner]));
	}
	}
	}
	int32x4_t sums_of_4_cells[kCells][4];
	for (int i = 0; i < 4; i++) {
	for (int cell = 0; cell < kCells; cell++) {
	sums_of_4_cells[cell][i] = vreinterpretq_s32_u32(
	vaddl_u16(vget_low_u16(sums_of_2_cells[cell][i]),
	vget_high_u16(sums_of_2_cells[cell][i])));
	}
	}
	// Update the rank_one_update vector
	for (int cell = 0; cell < kCells; cell++) {
	int32x4_t s01 =
	vaddq_s32(sums_of_4_cells[cell][0], sums_of_4_cells[cell][1]);
	int32x4_t s23 =
	vaddq_s32(sums_of_4_cells[cell][2], sums_of_4_cells[cell][3]);
	int32x4_t s = vaddq_s32(s01, s23);
	int32x4_t u = vmulq_n_s32(s, dst->rank_one_update_multiplier());
	std::int32_t* rank_one_update_ptr =
	dst->rank_one_update() + start_width + 4 * cell;
	vst1q_s32(rank_one_update_ptr,
	vaddq_s32(u, vld1q_s32(rank_one_update_ptr)));
	}
	dst->seek_forward_n_cells(kCells * kRegisterSize / kCellDepth);
	}
	};

	template <int Cells>
	using WidthMajorSideFormatNCells4x2 =
	KernelSideFormat<CellFormat<4, 2, CellOrder::WidthMajor>, Cells>;

	template <int Cells>
	class PackingRegisterBlock<
	WidthMajorUint8SideMap,
	PackedSideBlock<WidthMajorSideFormatNCells4x2<Cells> > >
	: public PackingRegisterBlockBase<
	WidthMajorUint8SideMap,
	PackedSideBlock<WidthMajorSideFormatNCells4x2<Cells> > > {
	public:
	typedef WidthMajorSideFormatNCells4x2<Cells> KernelSideFormat;
	typedef typename KernelSideFormat::Cell CellFormat;
	static const int kCells = KernelSideFormat::kCells;
	static const int kCellWidth = CellFormat::kWidth;
	static const int kKernelWidth = CellFormat::kWidth * kCells;
	static const int kCellDepth = CellFormat::kDepth;
	static const int kCellSize = CellFormat::kSize;

	typedef NEONPseudoRandomNonzeroBytesGenerator
	PseudoRandomNonzeroBytesGenerator;

	template <typename BitDepth, RoundingMode Rounding>
	void Pack(PackedSideBlock<KernelSideFormat>* dst, int start_width,
	PseudoRandomNonzeroBytesGenerator* prng) {
	static const int kBits = BitDepth::kBits;
	static const std::uint16_t kMaxVal = (1 << kBits) - 1;
	std::uint8_t* dst_ptr = dst->current_data();
	const std::uint8_t* src_ptr = this->complete_src_.data();
	const int stride = this->complete_src_.stride();
	// Load and requantize source WidthMajor data
	uint16x8_t src_lines[kCells * 4];
	for (int i = 0; i < kCells; i++) {
	// This packing path is used with our current
	// less-than-8-bit kernel, and the partial unrolling of this loop
	// results in substantially faster code (thanks to better
	// register allocation) on Nexus 5.

	#define GEMMLOWP_UNROLLED_LOOP_ITER(k) \
	src_lines[4 * i + k] = \
	vreinterpretq_u16_u8(Requantize<BitDepth, Rounding>( \
	vld1q_u8(src_ptr), prng)); \
	src_ptr += stride;

	GEMMLOWP_UNROLLED_LOOP_ITER(0)
	GEMMLOWP_UNROLLED_LOOP_ITER(1)
	GEMMLOWP_UNROLLED_LOOP_ITER(2)
	GEMMLOWP_UNROLLED_LOOP_ITER(3)

	#undef GEMMLOWP_UNROLLED_LOOP_ITER
	}
	// Reorder the data within registers to make WidthMajor 4x2 cells
	uint16x8x2_t src_lines_intertwined_2x[2 * kCells];
	for (int i = 0; i < kCells; i++) {
	src_lines_intertwined_2x[2 * i] =
	vzipq_u16(src_lines[4 * i], src_lines[4 * i + 2]);
	src_lines_intertwined_2x[2 * i + 1] =
	vzipq_u16(src_lines[4 * i + 1], src_lines[4 * i + 3]);
	}
	uint16x8x2_t src_lines_intertwined_4x[2 * kCells];
	for (int i = 0; i < kCells; i++) {
	src_lines_intertwined_4x[2 * i] =
	vzipq_u16(src_lines_intertwined_2x[2 * i].val[0],
	src_lines_intertwined_2x[2 * i + 1].val[0]);
	src_lines_intertwined_4x[2 * i + 1] =
	vzipq_u16(src_lines_intertwined_2x[2 * i].val[1],
	src_lines_intertwined_2x[2 * i + 1].val[1]);
	}
	// Store the resulting WidthMajor 4x2 cells in the destination packed block
	for (int outer = 0; outer < 2; outer++) {
	for (int inner = 0; inner < 2; inner++) {
	for (int cell = 0; cell < kCells; cell++) {
	uint8x8_t value = vreinterpret_u8_u16(vget_low_u16(
	src_lines_intertwined_4x[2 * cell + outer].val[inner]));
	vst1_u8(dst_ptr, value);
	dst_ptr += 8;
	}
	for (int cell = 0; cell < kCells; cell++) {
	uint8x8_t value = vreinterpret_u8_u16(vget_high_u16(
	src_lines_intertwined_4x[2 * cell + outer].val[inner]));
	vst1_u8(dst_ptr, value);
	dst_ptr += 8;
	}
	}
	}
	// Compute sums across the depth dimension
	uint16x8_t sums_of_2[kCells][4];
	for (int outer = 0; outer < 2; outer++) {
	for (int inner = 0; inner < 2; inner++) {
	int i = 2 * outer + inner;
	for (int cell = 0; cell < kCells; cell++) {
	sums_of_2[cell][i] = vpaddlq_u8(vreinterpretq_u8_u16(
	src_lines_intertwined_4x[2 * cell + outer].val[inner]));
	}
	}
	}
	uint16x8_t sums_of_4[kCells][2];
	for (int i = 0; i < 2; i++) {
	for (int cell = 0; cell < kCells; cell++) {
	sums_of_4[cell][i] =
	vaddq_u16(sums_of_2[cell][2 * i], sums_of_2[cell][2 * i + 1]);
	}
	}
	uint16x8_t sums_of_8[kCells];
	for (int cell = 0; cell < kCells; cell++) {
	sums_of_8[cell] = vaddq_u16(sums_of_4[cell][0], sums_of_4[cell][1]);
	}

	uint16x4_t sums_of_16[kCells];
	for (int cell = 0; cell < kCells; cell++) {
	sums_of_16[cell] = vadd_u16(vget_low_u16(sums_of_8[cell]),
	vget_high_u16(sums_of_8[cell]));
	}
	// Update the rank_one_update vector
	for (int cell = 0; cell < kCells; cell++) {
	int32x4_t s = vreinterpretq_s32_u32(vmovl_u16(sums_of_16[cell]));
	int32x4_t u = vmulq_n_s32(s, dst->rank_one_update_multiplier());
	std::int32_t* rank_one_update_ptr =
	dst->rank_one_update() + start_width + 4 * cell;
	vst1q_s32(rank_one_update_ptr,
	vaddq_s32(u, vld1q_s32(rank_one_update_ptr)));
	}
	dst->seek_forward_n_cells(kCells * kRegisterSize / kCellDepth);
	}
	};

	} // namespace gemmlowp

	#endif // GEMMLOWP_INTERNAL_PACK_NEON_H_