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  1. // This software is in the public domain. Where that dedication is not
  2. // recognized, you are granted a perpetual, irrevocable license to copy
  3. // and modify this file as you see fit.
  4.  
  5. #include <cstdio>
  6. #include <cstdint>
  7.  
  8. void gen_octaves_of_value_noise_linear(
  9.     uint32_t size,
  10.     uint32_t seed,
  11.     uint32_t octaves,
  12.     float a,
  13.     float *out)
  14. {
  15.     if(octaves==0) return;
  16.     if(octaves>31) octaves=31;
  17.     while(size&(size-1)) size&=size-1;
  18.     if(size==0) return;
  19.     float b;
  20.     uint32_t rnd=seed;
  21.     while((size>>(octaves-1))==0) --octaves;
  22.     for(uint32_t v=0;v<size;++v)
  23.         for(uint32_t u=0;u<size;++u)
  24.             out[v*size+u]=0.0f;
  25.     b=1.0f;
  26.     for(uint32_t i=0;i<octaves;++i)
  27.         b=1.0f+a*b;
  28.     b=1.0f/b;
  29.     for(uint32_t i=0;i<octaves;++i)
  30.     {
  31.         uint32_t cursize=size>>(octaves-i-1);
  32.         uint32_t step=1<<(octaves-i-1);
  33.         // upscale step
  34.         if(i>0)
  35.         {
  36.             uint32_t mask=cursize-1;
  37.             for(uint32_t v=0;v<cursize;v+=2)
  38.                 for(uint32_t u=1;u<cursize;u+=2)
  39.                     out[v*step*size+u*step]=0.5f*(
  40.                         out[v*step*size+((u-1)&mask)*step]+
  41.                         out[v*step*size+((u+1)&mask)*step]);
  42.             for(uint32_t v=1;v<cursize;v+=2)
  43.                 for(uint32_t u=0;u<cursize;++u)
  44.                     out[v*step*size+u*step]=0.5f*(
  45.                         out[((v-1)&mask)*step*size+u*step]+
  46.                         out[((v+1)&mask)*step*size+u*step]);
  47.         }
  48.         // white noise step
  49.         for(uint32_t v=0;v<cursize;++v)
  50.         {
  51.             uint32_t index=v*step*size;
  52.             for(uint32_t u=0;u<cursize;++u)
  53.             {
  54.                 float t=float(rnd)*2.32830644e-10; // 2^-32
  55.                 rnd=rnd*1103515245ul+12345ul; // glibc LCG
  56.                 out[index]+=b*t;
  57.                 index+=step;
  58.             }
  59.         }
  60.         b*=a;
  61.     }
  62. }
  63.  
  64. uint64_t rdtsc()
  65. {
  66.     uint64_t ret;
  67.     asm volatile
  68.     (
  69.         "rdtsc"
  70.         :"=A"(ret)
  71.     );
  72.     return ret;
  73. }
  74.  
  75. float image[1<<26];
  76.  
  77. int main()
  78. {
  79.     for(uint32_t N=32;N<=8192;N*=2)
  80.     {
  81.     	uint32_t octaves=7;
  82.         uint64_t tacts=rdtsc();
  83.         gen_octaves_of_value_noise_linear(N,0,7,0.73f,image);
  84.         tacts=rdtsc()-tacts;
  85.         printf("N=%d, time: %.0f tacts per texel.\n",N,double(tacts)/double(N*N));
  86.     }
  87.     for(uint32_t octaves=1;octaves<=16;++octaves)
  88.     {
  89.     	uint32_t N=256;
  90.         uint64_t tacts=rdtsc();
  91.         gen_octaves_of_value_noise_linear(N,0,octaves,0.73f,image);
  92.         tacts=rdtsc()-tacts;
  93.         printf("octaves=%d, time: %.0f tacts per texel.\n",octaves,double(tacts)/double(N*N));
  94.     }
  95.     return 0;
  96. }
  97.  
Success #stdin #stdout 3.31s 265280KB
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stdin
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Standard input is empty
stdout
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N=32, time: 80 tacts per texel.
N=64, time: 74 tacts per texel.
N=128, time: 75 tacts per texel.
N=256, time: 75 tacts per texel.
N=512, time: 78 tacts per texel.
N=1024, time: 79 tacts per texel.
N=2048, time: 80 tacts per texel.
N=4096, time: 82 tacts per texel.
N=8192, time: 86 tacts per texel.
octaves=1, time: 50 tacts per texel.
octaves=2, time: 65 tacts per texel.
octaves=3, time: 69 tacts per texel.
octaves=4, time: 70 tacts per texel.
octaves=5, time: 71 tacts per texel.
octaves=6, time: 71 tacts per texel.
octaves=7, time: 71 tacts per texel.
octaves=8, time: 71 tacts per texel.
octaves=9, time: 71 tacts per texel.
octaves=10, time: 71 tacts per texel.
octaves=11, time: 71 tacts per texel.
octaves=12, time: 71 tacts per texel.
octaves=13, time: 71 tacts per texel.
octaves=14, time: 71 tacts per texel.
octaves=15, time: 71 tacts per texel.
octaves=16, time: 71 tacts per texel.
https://ideone.com/2VP3jg
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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