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  1. #include <iostream>
  2. #include <iomanip>
  3. #include <vector>
  4. #include <cmath>
  5. using namespace std;
  6.  
  7. typedef unsigned char uchar;
  8. struct float3 {
  9.     float x, y, z;
  10. };
  11. ostream &operator<<(ostream &out, float3 v) {
  12.     return out << fixed << setprecision(2) << "float3( "
  13.         << setw(5) << v.x << ","
  14.         << setw(5) << v.y << ","
  15.         << setw(5) << v.z << " )";
  16. }
  17. struct uchar4 {
  18.     uchar x, y, z, w;
  19. };
  20. ostream &operator<<(ostream &out, uchar4 v) {
  21.     return out << "uchar4( "
  22.         << setw(3) << (int)v.x << ","
  23.         << setw(3) << (int)v.y << ","
  24.         << setw(3) << (int)v.z << ","
  25.         << setw(3) << (int)v.w << " )";
  26. }
  27.  
  28.  
  29. float3 unpackCompactVector(uchar4 packed) {
  30.     float exp = (float)(packed.w & 0x1F) - 16.0;
  31.     float factor = exp2(exp) / 256.0;
  32.     float x = (float)(packed.x) * factor * (packed.w & 0x20 ? -1.0 : 1.0);
  33.     float y = (float)(packed.y) * factor * (packed.w & 0x40 ? -1.0 : 1.0);
  34.     float z = (float)(packed.z) * factor * (packed.w & 0x80 ? -1.0 : 1.0);
  35.     float3 result = { x, y, z };
  36.     return result;
  37. }
  38.  
  39. uchar4 packCompactVector(float3 vec) {
  40.     float xAbs = abs(vec.x);   uchar xSign = vec.x < 0.0 ? 0x20 : 0;
  41.     float yAbs = abs(vec.y);   uchar ySign = vec.y < 0.0 ? 0x40 : 0;
  42.     float zAbs = abs(vec.z);   uchar zSign = vec.z < 0.0 ? 0x80 : 0;
  43.     float maxAbs = max(max(xAbs, yAbs), zAbs);
  44.     int exp = floor(log2(maxAbs)) + 1;
  45.     float factor = exp2(exp);
  46.     uchar xMant = floor(xAbs / factor * 256);
  47.     uchar yMant = floor(yAbs / factor * 256);
  48.     uchar zMant = floor(zAbs / factor * 256);
  49.     uchar w = ((exp + 16) & 0x1F) + xSign + ySign + zSign;
  50.     uchar4 result = { xMant, yMant, zMant, w };
  51.     return result;
  52. }
  53.  
  54.  
  55.  
  56. int main() {
  57.     vector<float3> testCases = {
  58.         { 1.0, 3.0, 7.95 },
  59.         { 1.0, 3.0, 7.98 },
  60.         { 1.0,-3.0, 8.00 },
  61.         {-1.0, 3.0, 8.05 },
  62.         {-1.0,-3.0, 8.10 },
  63.     };
  64.     for (float3 v : testCases) {
  65.         uchar4 packed = packCompactVector(v);
  66.         float3 unpacked = unpackCompactVector(packed);
  67.         cout << v << " -> " << packed << " -> " << unpacked << endl;
  68.     }
  69. }
Success #stdin #stdout 0s 3032KB
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stdin
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Standard input is empty
stdout
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float3(  1.00, 3.00, 7.95 ) -> uchar4(  32, 96,254, 19 ) -> float3(  1.00, 3.00, 7.94 )
float3(  1.00, 3.00, 7.98 ) -> uchar4(  32, 96,255, 19 ) -> float3(  1.00, 3.00, 7.97 )
float3(  1.00,-3.00, 8.00 ) -> uchar4(  16, 48,128, 84 ) -> float3(  1.00,-3.00, 8.00 )
float3( -1.00, 3.00, 8.05 ) -> uchar4(  16, 48,128, 52 ) -> float3( -1.00, 3.00, 8.00 )
float3( -1.00,-3.00, 8.10 ) -> uchar4(  16, 48,129,116 ) -> float3( -1.00,-3.00, 8.06 )
https://ideone.com/FvOXOV
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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