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Name magic numbers + minor cache performance #5

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54 changes: 33 additions & 21 deletions phash/phash.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13,24 +13,28 @@
const int WIDTH = 32;
const int HEIGHT = 32;
const int FRAME_SIZE = WIDTH * HEIGHT;
const int UCOUNT = 8;
const int VCOUNT = 8;
const int UVSIZE = UCOUNT * VCOUNT;

const float PI = 3.14159265358979323846f;
float cos_table_x[32][8];
float cos_table_y[32][8];
const float ISQRT_2 = 0.70710678118654752440f;
float cos_table_x[WIDTH][UCOUNT];
float cos_table_y[HEIGHT][VCOUNT];

// Compute 2D DCT on 32x32 input and return top-left 8x8 coefficients
void dct8x8(const uint8_t* input, float out[8][8]) {
for (int u = 0; u < 8; ++u) {
for (int v = 0; v < 8; ++v) {
void dct8x8(const uint8_t* input, float out[UCOUNT][VCOUNT]) {
for (int u = 0; u < UCOUNT; ++u) {
for (int v = 0; v < VCOUNT; ++v) {
float sum = 0.0f;
for (int x = 0; x < WIDTH; ++x) {
for (int y = 0; y < HEIGHT; ++y) {
for (int y = 0; y < HEIGHT; ++y) {
for (int x = 0; x < WIDTH; ++x) {
float pixel = static_cast<float>(input[y * WIDTH + x]);
sum += pixel * cos_table_x[x][u] * cos_table_y[y][v];
}
}
float cu = (u == 0) ? (1.0f / std::sqrt(2.0f)) : 1.0f;
float cv = (v == 0) ? (1.0f / std::sqrt(2.0f)) : 1.0f;
float cu = (u == 0) ? ISQRT_2 : 1.0f;
float cv = (v == 0) ? ISQRT_2 : 1.0f;
out[u][v] = 0.25f * cu * cv * sum;
}
}
Expand All @@ -43,17 +47,19 @@ uint64_t compute_phash(const uint8_t* frame) {

// Compute average of top-left 8x8 coefficients
float total = 0.0f;
for (int u = 0; u < 8; ++u)
for (int v = 0; v < 8; ++v)
for (int u = 0; u < UCOUNT; ++u) {
for (int v = 0; v < VCOUNT; ++v) {
total += dct[u][v];
float avg = total / 64.0f;
}
}
float avg = total / UVSIZE;

// Build 64-bit hash
uint64_t hash = 0;
for (int u = 0; u < 8; ++u) {
for (int v = 0; v < 8; ++v) {
for (int u = 0; u < UCOUNT; ++u) {
for (int v = 0; v < VCOUNT; ++v) {
hash <<= 1;
if (dct[u][v] > avg) hash |= 1;
hash |= dct[u][v] > avg;
}
}
return hash;
Expand Down Expand Up @@ -90,8 +96,9 @@ int main(int argc, char* argv[]) {

// Load all hashes
std::vector<uint64_t> target_hashes;
for (int i = 2; i < argc; ++i)
for (int i = 2; i < argc; ++i) {
target_hashes.push_back(parse_hex64(argv[i]));
}

FILE* f = fopen(input_file, "rb");
if (!f) {
Expand All @@ -100,13 +107,17 @@ int main(int argc, char* argv[]) {
}

// Precompute cosine tables
for (int x = 0; x < WIDTH; ++x)
for (int u = 0; u < 8; ++u)
for (int x = 0; x < WIDTH; ++x) {
for (int u = 0; u < UCOUNT; ++u) {
cos_table_x[x][u] = std::cos((2*x + 1) * u * PI / 64.0f);
}
}

for (int y = 0; y < HEIGHT; ++y)
for (int v = 0; v < 8; ++v)
for (int y = 0; y < HEIGHT; ++y) {
for (int v = 0; v < VCOUNT; ++v) {
cos_table_y[y][v] = std::cos((2*y + 1) * v * PI / 64.0f);
}
}

uint8_t frame[FRAME_SIZE];
int frame_num = 0;
Expand All @@ -116,9 +127,10 @@ int main(int argc, char* argv[]) {

for (size_t i = 0; i < target_hashes.size(); ++i) {
int dist = hamming(hash, target_hashes[i]);
if (dist <= 3 && target_hashes[i] != 0)
if (dist <= 3 && target_hashes[i] != 0) {
std::cout << std::hex << std::setw(16) << std::setfill('0') << target_hashes[i] << " "
<< std::hex << hash << " " << std::dec << dist << "\n";
}
}

frame_num++;
Expand Down