hash based motion estimation for screen data

Change-Id: Iec7969ffd8f53ca2f4eefd1d757cfec7b3bde131

av1/av1.cmake

@@ -476,6 +476,15 @@ if (CONFIG_WARPED_MOTION OR CONFIG_GLOBAL_MOTION)
   endif ()
 endif ()
 
+if (CONFIG_HASH_ME)
+  set(AOM_AV1_ENCODER_SOURCES
+      ${AOM_AV1_ENCODER_SOURCES}
+      "${AOM_ROOT}/av1/encoder/hash_motion.h"
+      "${AOM_ROOT}/av1/encoder/hash_motion.c"
+      "${AOM_ROOT}/third_party/vector/vector.h"
+      "${AOM_ROOT}/third_party/vector/vector.c")
+endif ()
+
 # Setup AV1 common/decoder/encoder targets. The libaom target must exist before
 # this function is called.
 function (setup_av1_targets)

av1/av1_cx.mk

@@ -108,6 +108,12 @@ AV1_CX_SRCS-yes += encoder/temporal_filter.c
 AV1_CX_SRCS-yes += encoder/temporal_filter.h
 AV1_CX_SRCS-yes += encoder/mbgraph.c
 AV1_CX_SRCS-yes += encoder/mbgraph.h
+ifeq ($(CONFIG_HASH_ME),yes)
+AV1_CX_SRCS-yes += ../third_party/vector/vector.h
+AV1_CX_SRCS-yes += ../third_party/vector/vector.c
+AV1_CX_SRCS-yes += encoder/hash_motion.c
+AV1_CX_SRCS-yes += encoder/hash_motion.h
+endif
 ifeq ($(CONFIG_CDEF),yes)
 AV1_CX_SRCS-yes += encoder/pickcdef.c
 endif

av1/common/alloccommon.c

@@ -86,6 +86,9 @@ void av1_free_ref_frame_buffers(BufferPool *pool) {
     aom_free(pool->frame_bufs[i].mvs);
     pool->frame_bufs[i].mvs = NULL;
     aom_free_frame_buffer(&pool->frame_bufs[i].buf);
+#if CONFIG_HASH_ME
+    av1_hash_table_destroy(&pool->frame_bufs[i].hash_table);
+#endif
   }
 }
 

av1/common/onyxc_int.h

@@ -38,6 +38,10 @@
 #if CONFIG_CFL
 #include "av1/common/cfl.h"
 #endif
+#if CONFIG_HASH_ME
+// TODO(youzhou@microsoft.com): Encoder only. Move it out of common
+#include "av1/encoder/hash_motion.h"
+#endif
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -127,6 +131,9 @@ typedef struct {
 #endif  // CONFIG_GLOBAL_MOTION
   aom_codec_frame_buffer_t raw_frame_buffer;
   YV12_BUFFER_CONFIG buf;
+#if CONFIG_HASH_ME
+  hash_table hash_table;
+#endif
 #if CONFIG_TEMPMV_SIGNALING
   uint8_t intra_only;
 #endif

av1/encoder/encoder.c

@@ -45,6 +45,9 @@
 #endif
 #include "av1/encoder/ethread.h"
 #include "av1/encoder/firstpass.h"
+#if CONFIG_HASH_ME
+#include "av1/encoder/hash_motion.h"
+#endif
 #include "av1/encoder/mbgraph.h"
 #include "av1/encoder/picklpf.h"
 #if CONFIG_LOOP_RESTORATION
@@ -5362,6 +5365,11 @@ static void init_ref_frame_bufs(AV1_COMMON *cm) {
     cm->ref_frame_map[i] = INVALID_IDX;
     pool->frame_bufs[i].ref_count = 0;
   }
+#if CONFIG_HASH_ME
+  for (i = 0; i < FRAME_BUFFERS; ++i) {
+    av1_hash_table_init(&pool->frame_bufs[i].hash_table);
+  }
+#endif
 }
 
 static void check_initial_width(AV1_COMP *cpi,
@@ -6085,6 +6093,71 @@ int av1_get_compressed_data(AV1_COMP *cpi, unsigned int *frame_flags,
     Pass0Encode(cpi, size, dest, 0, frame_flags);
   }
 #endif
+#if CONFIG_HASH_ME
+  if (oxcf->pass != 1 && cpi->common.allow_screen_content_tools) {
+    // add to hash table
+    const int pic_width = cpi->source->y_crop_width;
+    const int pic_height = cpi->source->y_crop_height;
+    uint32_t *block_hash_values[2][2];
+    int8_t *is_block_same[2][3];
+    int k, j;
+
+    for (k = 0; k < 2; k++) {
+      for (j = 0; j < 2; j++) {
+        CHECK_MEM_ERROR(cm, block_hash_values[k][j],
+                        aom_malloc(sizeof(uint32_t) * pic_width * pic_height));
+      }
+
+      for (j = 0; j < 3; j++) {
+        CHECK_MEM_ERROR(cm, is_block_same[k][j],
+                        aom_malloc(sizeof(int8_t) * pic_width * pic_height));
+      }
+    }
+
+    av1_hash_table_create(&cm->cur_frame->hash_table);
+    av1_generate_block_2x2_hash_value(cpi->source, block_hash_values[0],
+                                      is_block_same[0]);
+    av1_generate_block_hash_value(cpi->source, 4, block_hash_values[0],
+                                  block_hash_values[1], is_block_same[0],
+                                  is_block_same[1]);
+    av1_generate_block_hash_value(cpi->source, 8, block_hash_values[1],
+                                  block_hash_values[0], is_block_same[1],
+                                  is_block_same[0]);
+    av1_add_to_hash_map_by_row_with_precal_data(
+        &cm->cur_frame->hash_table, block_hash_values[0], is_block_same[0][2],
+        pic_width, pic_height, 8);
+    av1_generate_block_hash_value(cpi->source, 16, block_hash_values[0],
+                                  block_hash_values[1], is_block_same[0],
+                                  is_block_same[1]);
+    av1_add_to_hash_map_by_row_with_precal_data(
+        &cm->cur_frame->hash_table, block_hash_values[1], is_block_same[1][2],
+        pic_width, pic_height, 16);
+    av1_generate_block_hash_value(cpi->source, 32, block_hash_values[1],
+                                  block_hash_values[0], is_block_same[1],
+                                  is_block_same[0]);
+    av1_add_to_hash_map_by_row_with_precal_data(
+        &cm->cur_frame->hash_table, block_hash_values[0], is_block_same[0][2],
+        pic_width, pic_height, 32);
+    av1_generate_block_hash_value(cpi->source, 64, block_hash_values[0],
+                                  block_hash_values[1], is_block_same[0],
+                                  is_block_same[1]);
+    av1_add_to_hash_map_by_row_with_precal_data(
+        &cm->cur_frame->hash_table, block_hash_values[1], is_block_same[1][2],
+        pic_width, pic_height, 64);
+
+    for (k = 0; k < 2; k++) {
+      for (j = 0; j < 2; j++) {
+        aom_free(block_hash_values[k][j]);
+      }
+
+      for (j = 0; j < 3; j++) {
+        aom_free(is_block_same[k][j]);
+      }
+    }
+  }
+
+#endif
+
 #if CONFIG_NO_FRAME_CONTEXT_SIGNALING
   cm->frame_contexts[cm->new_fb_idx] = *cm->fc;
 #else

av1/encoder/encoder.h

@@ -692,6 +692,17 @@ static INLINE int get_ref_frame_buf_idx(const AV1_COMP *cpi,
   return (map_idx != INVALID_IDX) ? cm->ref_frame_map[map_idx] : INVALID_IDX;
 }
 
+#if CONFIG_HASH_ME
+static INLINE hash_table *get_ref_frame_hash_map(const AV1_COMP *cpi,
+                                                 MV_REFERENCE_FRAME ref_frame) {
+  const AV1_COMMON *const cm = &cpi->common;
+  const int buf_idx = get_ref_frame_buf_idx(cpi, ref_frame);
+  return buf_idx != INVALID_IDX
+             ? &cm->buffer_pool->frame_bufs[buf_idx].hash_table
+             : NULL;
+}
+#endif
+
 static INLINE YV12_BUFFER_CONFIG *get_ref_frame_buffer(
     const AV1_COMP *cpi, MV_REFERENCE_FRAME ref_frame) {
   const AV1_COMMON *const cm = &cpi->common;

av1/encoder/hash_motion.c

+#include <assert.h>
+#include "av1/encoder/hash_motion.h"
+#include "./av1_rtcd.h"
+
+typedef struct _crc_calculator {
+  uint32_t remainder;
+  uint32_t trunc_poly;
+  uint32_t bits;
+  uint32_t table[256];
+  uint32_t final_result_mask;
+} crc_calculator;
+
+static void crc_calculator_process_data(crc_calculator *p_crc_calculator,
+                                        uint8_t *pData, uint32_t dataLength) {
+  for (uint32_t i = 0; i < dataLength; i++) {
+    const uint8_t index =
+        (p_crc_calculator->remainder >> (p_crc_calculator->bits - 8)) ^
+        pData[i];
+    p_crc_calculator->remainder <<= 8;
+    p_crc_calculator->remainder ^= p_crc_calculator->table[index];
+  }
+}
+
+static void crc_calculator_reset(crc_calculator *p_crc_calculator) {
+  p_crc_calculator->remainder = 0;
+}
+
+static uint32_t crc_calculator_get_crc(crc_calculator *p_crc_calculator) {
+  return p_crc_calculator->remainder & p_crc_calculator->final_result_mask;
+}
+
+static void crc_calculator_init_table(crc_calculator *p_crc_calculator) {
+  const uint32_t high_bit = 1 << (p_crc_calculator->bits - 1);
+  const uint32_t byte_high_bit = 1 << (8 - 1);
+
+  for (uint32_t value = 0; value < 256; value++) {
+    uint32_t remainder = 0;
+    for (uint8_t mask = byte_high_bit; mask != 0; mask >>= 1) {
+      if (value & mask) {
+        remainder ^= high_bit;
+      }
+
+      if (remainder & high_bit) {
+        remainder <<= 1;
+        remainder ^= p_crc_calculator->trunc_poly;
+      } else {
+        remainder <<= 1;
+      }
+    }
+    p_crc_calculator->table[value] = remainder;
+  }
+}
+
+static void crc_calculator_init(crc_calculator *p_crc_calculator, uint32_t bits,
+                                uint32_t truncPoly) {
+  p_crc_calculator->remainder = 0;
+  p_crc_calculator->bits = bits;
+  p_crc_calculator->trunc_poly = truncPoly;
+  p_crc_calculator->final_result_mask = (1 << bits) - 1;
+  crc_calculator_init_table(p_crc_calculator);
+}
+
+static const int crc_bits = 16;
+static const int block_size_bits = 2;
+
+static crc_calculator crc_calculator1;
+static crc_calculator crc_calculator2;
+static int g_crc_initialized = 0;
+
+static void hash_table_clear_all(hash_table *p_hash_table) {
+  if (p_hash_table->p_lookup_table == NULL) {
+    return;
+  }
+  int max_addr = 1 << (crc_bits + block_size_bits);
+  for (int i = 0; i < max_addr; i++) {
+    if (p_hash_table->p_lookup_table[i] != NULL) {
+      vector_destroy(p_hash_table->p_lookup_table[i]);
+      aom_free(p_hash_table->p_lookup_table[i]);
+      p_hash_table->p_lookup_table[i] = NULL;
+    }
+  }
+}
+
+static uint32_t get_crc_value1(uint8_t *p, int length) {
+  crc_calculator_reset(&crc_calculator1);
+  crc_calculator_process_data(&crc_calculator1, p, length);
+  return crc_calculator_get_crc(&crc_calculator1);
+}
+
+static uint32_t get_crc_value2(uint8_t *p, int length) {
+  crc_calculator_reset(&crc_calculator2);
+  crc_calculator_process_data(&crc_calculator2, p, length);
+  return crc_calculator_get_crc(&crc_calculator2);
+}
+
+// TODO(youzhou@microsoft.com): is higher than 8 bits screen content supported?
+// If yes, fix this function
+static void get_pixels_in_1D_char_array_by_block_2x2(uint8_t *y_src, int stride,
+                                                     uint8_t *p_pixels_in1D) {
+  uint8_t *p_pel = y_src;
+  int index = 0;
+  for (int i = 0; i < 2; i++) {
+    for (int j = 0; j < 2; j++) {
+      p_pixels_in1D[index++] = p_pel[j];
+    }
+    p_pel += stride;
+  }
+}
+
+static int is_block_2x2_row_same_value(uint8_t *p) {
+  if (p[0] != p[1] || p[2] != p[3]) {
+    return 0;
+  }
+
+  return 1;
+}
+
+static int is_block_2x2_col_same_value(uint8_t *p) {
+  if ((p[0] != p[2]) || (p[1] != p[3])) {
+    return 0;
+  }
+
+  return 1;
+}
+
+// the hash value (hash_value1 consists two parts, the first 2 bits relate to
+// the block size and the remaining 16 bits are the crc values. This fuction
+// is used to get the first 2 bits.
+static int hash_block_size_to_index(int block_size) {
+  switch (block_size) {
+    case 8: return 0;
+    case 16: return 1;
+    case 32: return 2;
+    case 64: return 3;
+    default: return -1;
+  }
+}
+
+void av1_hash_table_init(hash_table *p_hash_table) {
+  if (g_crc_initialized == 0) {
+    crc_calculator_init(&crc_calculator1, 24, 0x5D6DCB);
+    crc_calculator_init(&crc_calculator2, 24, 0x864CFB);
+    g_crc_initialized = 1;
+  }
+  p_hash_table->p_lookup_table = NULL;
+}
+
+void av1_hash_table_destroy(hash_table *p_hash_table) {
+  hash_table_clear_all(p_hash_table);
+  aom_free(p_hash_table->p_lookup_table);
+  p_hash_table->p_lookup_table = NULL;
+}
+
+void av1_hash_table_create(hash_table *p_hash_table) {
+  if (p_hash_table->p_lookup_table != NULL) {
+    hash_table_clear_all(p_hash_table);
+    return;
+  }
+  const int max_addr = 1 << (crc_bits + block_size_bits);
+  p_hash_table->p_lookup_table =
+      (Vector **)aom_malloc(sizeof(p_hash_table->p_lookup_table[0]) * max_addr);
+  memset(p_hash_table->p_lookup_table, 0,
+         sizeof(p_hash_table->p_lookup_table[0]) * max_addr);
+}
+
+static void hash_table_add_to_table(hash_table *p_hash_table,
+                                    uint32_t hash_value,
+                                    block_hash *curr_block_hash) {
+  if (p_hash_table->p_lookup_table[hash_value] == NULL) {
+    p_hash_table->p_lookup_table[hash_value] =
+        aom_malloc(sizeof(p_hash_table->p_lookup_table[0][0]));
+    vector_setup(p_hash_table->p_lookup_table[hash_value], 10,
+                 sizeof(curr_block_hash[0]));
+    vector_push_back(p_hash_table->p_lookup_table[hash_value], curr_block_hash);
+  } else {
+    vector_push_back(p_hash_table->p_lookup_table[hash_value], curr_block_hash);
+  }
+}
+
+int32_t av1_hash_table_count(hash_table *p_hash_table, uint32_t hash_value) {
+  if (p_hash_table->p_lookup_table[hash_value] == NULL) {
+    return 0;
+  } else {
+    return (int32_t)(p_hash_table->p_lookup_table[hash_value]->size);
+  }
+}
+
+Iterator av1_hash_get_first_iterator(hash_table *p_hash_table,
+                                     uint32_t hash_value) {
+  assert(av1_hash_table_count(p_hash_table, hash_value) > 0);
+  return vector_begin(p_hash_table->p_lookup_table[hash_value]);
+}
+
+int32_t av1_has_exact_match(hash_table *p_hash_table, uint32_t hash_value1,
+                            uint32_t hash_value2) {
+  if (p_hash_table->p_lookup_table[hash_value1] == NULL) {
+    return 0;
+  }
+  Iterator iterator = vector_begin(p_hash_table->p_lookup_table[hash_value1]);
+  Iterator last = vector_end(p_hash_table->p_lookup_table[hash_value1]);
+  for (; !iterator_equals(&iterator, &last); iterator_increment(&iterator)) {
+    if ((*(block_hash *)iterator_get(&iterator)).hash_value2 == hash_value2) {
+      return 1;
+    }
+  }
+  return 0;
+}
+
+void av1_generate_block_2x2_hash_value(const YV12_BUFFER_CONFIG *picture,
+                                       uint32_t *pic_block_hash[2],
+                                       int8_t *pic_block_same_info[3]) {
+  const int width = 2;
+  const int height = 2;
+  const int x_end = picture->y_crop_width - width + 1;
+  const int y_end = picture->y_crop_height - height + 1;
+
+  const int length = width * 2;
+  uint8_t p[4];
+
+  int pos = 0;
+  for (int y_pos = 0; y_pos < y_end; y_pos++) {
+    for (int x_pos = 0; x_pos < x_end; x_pos++) {
+      get_pixels_in_1D_char_array_by_block_2x2(
+          picture->y_buffer + y_pos * picture->y_stride + x_pos,
+          picture->y_stride, p);
+      pic_block_same_info[0][pos] = is_block_2x2_row_same_value(p);
+      pic_block_same_info[1][pos] = is_block_2x2_col_same_value(p);
+
+      pic_block_hash[0][pos] = get_crc_value1(p, length * sizeof(p[0]));
+      pic_block_hash[1][pos] = get_crc_value2(p, length * sizeof(p[0]));
+
+      pos++;
+    }
+    pos += width - 1;
+  }
+}
+
+void av1_generate_block_hash_value(const YV12_BUFFER_CONFIG *picture,
+                                   int block_size,
+                                   uint32_t *src_pic_block_hash[2],
+                                   uint32_t *dst_pic_block_hash[2],
+                                   int8_t *src_pic_block_same_info[3],
+                                   int8_t *dst_pic_block_same_info[3]) {
+  const int pic_width = picture->y_crop_width;
+  const int x_end = picture->y_crop_width - block_size + 1;
+  const int y_end = picture->y_crop_height - block_size + 1;
+
+  const int src_size = block_size >> 1;
+  const int quad_size = block_size >> 2;
+
+  uint32_t p[4];
+  const int length = sizeof(p);
+
+  int pos = 0;
+  for (int y_pos = 0; y_pos < y_end; y_pos++) {
+    for (int x_pos = 0; x_pos < x_end; x_pos++) {
+      p[0] = src_pic_block_hash[0][pos];
+      p[1] = src_pic_block_hash[0][pos + src_size];
+      p[2] = src_pic_block_hash[0][pos + src_size * pic_width];
+      p[3] = src_pic_block_hash[0][pos + src_size * pic_width + src_size];
+      dst_pic_block_hash[0][pos] = get_crc_value1((uint8_t *)p, length);
+
+      p[0] = src_pic_block_hash[1][pos];
+      p[1] = src_pic_block_hash[1][pos + src_size];
+      p[2] = src_pic_block_hash[1][pos + src_size * pic_width];
+      p[3] = src_pic_block_hash[1][pos + src_size * pic_width + src_size];
+      dst_pic_block_hash[1][pos] = get_crc_value2((uint8_t *)p, length);
+
+      dst_pic_block_same_info[0][pos] =
+          src_pic_block_same_info[0][pos] &&
+          src_pic_block_same_info[0][pos + quad_size] &&
+          src_pic_block_same_info[0][pos + src_size] &&
+          src_pic_block_same_info[0][pos + src_size * pic_width] &&
+          src_pic_block_same_info[0][pos + src_size * pic_width + quad_size] &&
+          src_pic_block_same_info[0][pos + src_size * pic_width + src_size];
+
+      dst_pic_block_same_info[1][pos] =
+          src_pic_block_same_info[1][pos] &&
+          src_pic_block_same_info[1][pos + src_size] &&
+          src_pic_block_same_info[1][pos + quad_size * pic_width] &&
+          src_pic_block_same_info[1][pos + quad_size * pic_width + src_size] &&
+          src_pic_block_same_info[1][pos + src_size * pic_width] &&
+          src_pic_block_same_info[1][pos + src_size * pic_width + src_size];
+      pos++;
+    }
+    pos += block_size - 1;
+  }
+
+  if (block_size >= 8) {
+    const int size_minus1 = block_size - 1;
+    pos = 0;
+    for (int y_pos = 0; y_pos < y_end; y_pos++) {
+      for (int x_pos = 0; x_pos < x_end; x_pos++) {
+        dst_pic_block_same_info[2][pos] =
+            (!dst_pic_block_same_info[0][pos] &&
+             !dst_pic_block_same_info[1][pos]) ||
+            (((x_pos & size_minus1) == 0) && ((y_pos & size_minus1) == 0));
+        pos++;
+      }
+      pos += block_size - 1;
+    }
+  }
+}
+
+void av1_add_to_hash_map_by_row_with_precal_data(hash_table *p_hash_table,
+                                                 uint32_t *pic_hash[2],
+                                                 int8_t *pic_is_same,
+                                                 int pic_width, int pic_height,
+                                                 int block_size) {
+  const int x_end = pic_width - block_size + 1;
+  const int y_end = pic_height - block_size + 1;
+
+  const int8_t *src_is_added = pic_is_same;
+  const uint32_t *src_hash[2] = { pic_hash[0], pic_hash[1] };
+
+  int add_value = hash_block_size_to_index(block_size);
+  assert(add_value >= 0);
+  add_value <<= crc_bits;
+  const int crc_mask = (1 << crc_bits) - 1;
+
+  for (int x_pos = 0; x_pos < x_end; x_pos++) {
+    for (int y_pos = 0; y_pos < y_end; y_pos++) {
+      const int pos = y_pos * pic_width + x_pos;
+      // valid data
+      if (src_is_added[pos]) {
+        block_hash curr_block_hash;
+        curr_block_hash.x = x_pos;
+        curr_block_hash.y = y_pos;
+
+        const uint32_t hash_value1 = (src_hash[0][pos] & crc_mask) + add_value;
+        curr_block_hash.hash_value2 = src_hash[1][pos];
+
+        hash_table_add_to_table(p_hash_table, hash_value1, &curr_block_hash);
+      }
+    }
+  }
+}
+
+int av1_hash_is_horizontal_perfect(const YV12_BUFFER_CONFIG *picture,
+                                   int block_size, int x_start, int y_start) {
+  const int stride = picture->y_stride;
+  const uint8_t *p = picture->y_buffer + y_start * stride + x_start;
+
+  for (int i = 0; i < block_size; i++) {
+    for (int j = 1; j < block_size; j++) {
+      if (p[j] != p[0]) {
+        return 0;
+      }
+    }
+    p += stride;
+  }
+
+  return 1;
+}
+
+int av1_hash_is_vertical_perfect(const YV12_BUFFER_CONFIG *picture,
+                                 int block_size, int x_start, int y_start) {
+  const int stride = picture->y_stride;
+  const uint8_t *p = picture->y_buffer + y_start * stride + x_start;
+
+  for (int i = 0; i < block_size; i++) {
+    for (int j = 1; j < block_size; j++) {
+      if (p[j * stride + i] != p[i]) {
+        return 0;
+      }
+    }
+  }
+
+  return 1;
+}
+
+// global buffer for hash value calculation of a block
+// used only in av1_get_block_hash_value()
+static uint32_t hash_value_buffer[2][2][1024];  // [first hash/second hash]
+                                                // [two buffers used ping-pong]
+                                                // [num of 2x2 blocks in 64x64]
+
+void av1_get_block_hash_value(uint8_t *y_src, int stride, int block_size,
+                              uint32_t *hash_value1, uint32_t *hash_value2) {
+  uint8_t pixel_to_hash[4];
+  uint32_t to_hash[4];
+  const int add_value = hash_block_size_to_index(block_size) << crc_bits;
+  assert(add_value >= 0);
+  const int crc_mask = (1 << crc_bits) - 1;
+
+  // 2x2 subblock hash values in current CU
+  int sub_block_in_width = (block_size >> 1);
+  for (int y_pos = 0; y_pos < block_size; y_pos += 2) {
+    for (int x_pos = 0; x_pos < block_size; x_pos += 2) {
+      int pos = (y_pos >> 1) * sub_block_in_width + (x_pos >> 1);
+      get_pixels_in_1D_char_array_by_block_2x2(y_src + y_pos * stride + x_pos,
+                                               stride, pixel_to_hash);
+
+      hash_value_buffer[0][0][pos] =
+          get_crc_value1(pixel_to_hash, sizeof(pixel_to_hash));
+      hash_value_buffer[1][0][pos] =
+          get_crc_value2(pixel_to_hash, sizeof(pixel_to_hash));
+    }
+  }
+
+  int src_sub_block_in_width = sub_block_in_width;
+  sub_block_in_width >>= 1;
+
+  int src_idx = 1;
+  int dst_idx = 0;
+
+  // 4x4 subblock hash values to current block hash values
+  for (int sub_width = 4; sub_width <= block_size; sub_width *= 2) {
+    src_idx = 1 - src_idx;
+    dst_idx = 1 - dst_idx;
+
+    int dst_pos = 0;
+    for (int y_pos = 0; y_pos < sub_block_in_width; y_pos++) {
+      for (int x_pos = 0; x_pos < sub_block_in_width; x_pos++) {
+        int srcPos = (y_pos << 1) * src_sub_block_in_width + (x_pos << 1);
+
+        to_hash[0] = hash_value_buffer[0][src_idx][srcPos];
+        to_hash[1] = hash_value_buffer[0][src_idx][srcPos + 1];
+        to_hash[2] =
+            hash_value_buffer[0][src_idx][srcPos + src_sub_block_in_width];
+        to_hash[3] =
+            hash_value_buffer[0][src_idx][srcPos + src_sub_block_in_width + 1];
+
+        hash_value_buffer[0][dst_idx][dst_pos] =