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  1. #include <stdlib.h>
  2. #include <stdio.h>
  3. #include <time.h>
  4.  
  5. #define MAX_COUNT (1 << 29)
  6. size_t counter = 0;
  7.  
  8. size_t testSwitch()
  9. {
  10.     clock_t start = clock();
  11.     size_t i;
  12.     for (i = 0; i < MAX_COUNT; i++)
  13.     {
  14.         switch (counter % 4 + 1)
  15.         {
  16.             case 1: counter += 4; break;
  17.             case 2: counter += 3; break;
  18.             case 3: counter += 2; break;
  19.             case 4: counter += 1; break;
  20.         }
  21.     }
  22.     return 1000 * (clock() - start) / CLOCKS_PER_SEC;
  23. }
  24.  
  25. size_t testIf()
  26. {
  27.     clock_t start = clock();
  28.     size_t i;
  29.     for (i = 0; i < MAX_COUNT; i++)
  30.     {
  31.         // Теперь вычисления идут прямо в условиях, без промежуточной константы
  32.         if (counter % 4 + 1 == 1) { counter += 4; }
  33.         else if (counter % 4 + 1 == 2) { counter += 3; }
  34.         else if (counter % 4 + 1 == 3) { counter += 2; }
  35.         else if (counter % 4 + 1 == 4) { counter += 1; }
  36.     }
  37.     return 1000 * (clock() - start) / CLOCKS_PER_SEC;
  38. }
  39.  
  40.  
  41. int main()
  42. {
  43.     printf("Starting...\n");
  44.     printf("Switch statement: %u ms\n", testSwitch());
  45.     printf("If     statement: %u ms\n", testIf());
  46. }
Success #stdin #stdout 1.29s 5312KB
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Standard input is empty
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Starting...
Switch statement: 1004 ms
If     statement: 279 ms
https://ideone.com/WvY7g9
language:
C (gcc 8.3)
created:
2 days ago
visibility:
public

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