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  1.     #include <iostream>
  2.     #include <cstring>
  3.     #include <chrono>
  4.  
  5.     // 8Kb of space.
  6.     char smallSpace[8 * 1024];
  7.  
  8.     // 64Mb of space (larger than cache)
  9.     char bigSpace[64 * 1024 * 1024];
  10.  
  11.     void populateSpaces(char val)
  12.     {
  13.         memset(smallSpace, val, sizeof(smallSpace));
  14.         memset(bigSpace, val, sizeof(bigSpace));
  15.         std::cout << "Populated spaces" << std::endl;
  16.     }
  17.  
  18.     unsigned int doWork(char* ptr, size_t size)
  19.     {
  20.     	unsigned int total = 0;
  21.     	const char* end = ptr + size;
  22.     	while (ptr < end) {
  23.     		total += *(ptr++);
  24.     	}
  25.     	return total;
  26.     }
  27.  
  28.     unsigned int strideWork(char* ptr, size_t size)
  29.     {
  30.     	unsigned int total = 0;
  31.     	const char* end = ptr + size;
  32.     	const size_t StrideRate = 1024;
  33.     	for (size_t i = 0; i < StrideRate; ++i, ++ptr) {
  34.     		while (ptr < end) {
  35.     			total += (*ptr++);
  36.     		}
  37.     	}
  38.     	return total;
  39.     }
  40.  
  41. 	using namespace std;
  42. 	using namespace chrono;
  43.  
  44. 	void doTiming(unsigned int (*function)(char*, size_t), const char* label, char* ptr, size_t size)
  45. 	{
  46. 		cout << label << ": ";
  47. 		const high_resolution_clock::time_point start = high_resolution_clock::now();
  48. 		auto result = function(ptr, size);
  49. 		const high_resolution_clock::time_point stop = high_resolution_clock::now();
  50. 		auto delta = duration_cast<nanoseconds>(stop - start).count();
  51. 		cout << "took " << delta << "ns (result is " << result << ")" << endl;
  52. 	}
  53.  
  54.     int main()
  55.     {
  56. 		cout << "Timer resultion is " << 
  57. 			duration_cast<nanoseconds>(high_resolution_clock::duration(1)).count()
  58. 			<< "ns" << endl;
  59.  
  60. 		populateSpaces(1);
  61.  
  62. 		doTiming(doWork, "doWork/small", smallSpace, sizeof(smallSpace));
  63. 		doTiming(doWork, "doWork/small", smallSpace, sizeof(smallSpace));
  64. 		doTiming(doWork, "doWork/small", smallSpace, sizeof(smallSpace));
  65. 		doTiming(doWork, "doWork/big", bigSpace, sizeof(bigSpace));
  66. 		doTiming(doWork, "doWork/big", bigSpace, sizeof(bigSpace));
  67. 		doTiming(doWork, "doWork/small", smallSpace, sizeof(smallSpace));
  68. 		doTiming(doWork, "doWork/small", smallSpace, sizeof(smallSpace));
  69. 		doTiming(doWork, "doWork/small", smallSpace, sizeof(smallSpace));
  70.  
  71. 		populateSpaces(2);		
  72.  
  73. 		doTiming(strideWork, "strideWork/small", smallSpace, sizeof(smallSpace));
  74. 		doTiming(strideWork, "strideWork/small", smallSpace, sizeof(smallSpace));
  75. 		doTiming(strideWork, "strideWork/small", smallSpace, sizeof(smallSpace));
  76. 		doTiming(strideWork, "strideWork/big", bigSpace, sizeof(bigSpace));
  77. 		doTiming(strideWork, "strideWork/big", bigSpace, sizeof(bigSpace));
  78.     }
Success #stdin #stdout 0.33s 68864KB
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stdin
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Standard input is empty
stdout
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Timer resultion is 1ns
Populated spaces
doWork/small: took 8384ns (result is 8192)
doWork/small: took 7702ns (result is 8192)
doWork/small: took 7686ns (result is 8192)
doWork/big: took 64921206ns (result is 67108864)
doWork/big: took 65120677ns (result is 67108864)
doWork/small: took 8237ns (result is 8192)
doWork/small: took 7678ns (result is 8192)
doWork/small: took 7677ns (result is 8192)
Populated spaces
strideWork/small: took 10112ns (result is 16384)
strideWork/small: took 9570ns (result is 16384)
strideWork/small: took 9559ns (result is 16384)
strideWork/big: took 65512138ns (result is 134217728)
strideWork/big: took 65005505ns (result is 134217728)
https://ideone.com/9zOW5q
Comparison of memory access timings
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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