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  1.  
  2. #include <stdlib.h>
  3. #include <time.h>
  4. #include <stdio.h>
  5.  
  6. #define TIMES 200000000
  7.  
  8. int main(){
  9.     volatile int a;
  10.     volatile int b;
  11.     volatile int c;
  12.     int i;
  13.     clock_t t1 = clock();
  14.  
  15.     srand(time(NULL));
  16.     a = rand();
  17.     b = rand();
  18.  
  19. 	// # on x86_64 gcc 4.8.1
  20.  
  21.     for( i = 0; i < TIMES; i++ ){
  22.         c = a;
  23.         // movl    -36(%rbp), %eax
  24. 		// movl    %eax, -44(%rbp)
  25.  
  26.         a = b;
  27. 	    // movl    -40(%rbp), %eax
  28. 	    // movl    %eax, -36(%rbp)
  29.  
  30.         b = c;
  31. 	    // movl    -44(%rbp), %eax
  32. 	    // movl    %eax, -40(%rbp)
  33.     }
  34.  
  35.     clock_t t2 = clock();
  36.     for( i = 0; i < TIMES; i++ ){
  37.         a ^= b;
  38.         // movl    -36(%rbp), %edx
  39.         // movl    -40(%rbp), %eax
  40.         // xorl    %edx, %eax
  41.         // movl    %eax, -36(%rbp)
  42.         b ^= a;
  43. 	    // movl    -40(%rbp), %edx
  44.     	// movl    -36(%rbp), %eax
  45.     	// xorl    %edx, %eax
  46.     	// movl    %eax, -40(%rbp)
  47.         a ^= b;
  48.     	// movl    -36(%rbp), %edx
  49.     	// movl    -40(%rbp), %eax
  50.     	// xorl    %edx, %eax
  51.     	// movl    %eax, -36(%rbp)
  52.     }
  53.     clock_t t3 = clock();
  54.     double s_var = (double)(t2-t1)/CLOCKS_PER_SEC;
  55.     double s_xor = (double)(t3-t2)/CLOCKS_PER_SEC;
  56.     double s_all = (double)(t3-t1)/CLOCKS_PER_SEC;
  57.  
  58.     printf("swap by var: %.2fs\n",s_var);
  59.     printf("swap by xor: %.2fs\n",s_xor);
  60.     printf("ratio%% var: %d\n",(int)((s_var/s_all)*100));
  61.     printf("ratio%% xor: %d\n",(int)((s_xor/s_all)*100));
  62.     printf("xor/var: %.2f\n",(s_xor/s_var));
  63. 	return 0;
  64. }
Success #stdin #stdout 2.45s 2248KB
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stdin
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Standard input is empty
stdout
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swap by var: 0.72s
swap by xor: 1.73s
ratio% var: 29
ratio% xor: 70
xor/var: 2.40
https://ideone.com/wvrCRn
language:
C (gcc 8.3)
created:
10 years ago
visibility:
public

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