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  1. #include <iostream>
  2. #include <chrono>
  3. #include <unordered_map>
  4. #include <algorithm>
  5. #include <random>
  6.  
  7. using namespace std; 
  8.  
  9. int hextoint1 (char number)
  10. {
  11. 	if (number == '0') 
  12. 		return 0;
  13. 	if (number == '1')
  14. 		return 1;
  15. 	if (number == '2') 
  16. 		return 2;
  17. 	if (number == '3')
  18. 		return 3;
  19. 	if (number == '4')
  20. 		return 4;
  21. 	if (number == '5')
  22. 		return 5;
  23. 	if (number == '6')
  24. 		return 6;
  25. 	if (number == '7')
  26. 		return 7;
  27. 	if (number == '8')
  28. 		return 8;
  29. 	if (number == '9') 
  30. 		return 9;
  31. 	if (number == 'a') 
  32. 		return 10;
  33. 	if (number == 'b') 
  34. 		return 11;
  35. 	if (number == 'c') 
  36. 		return 12;
  37. 	if (number == 'd') 
  38. 		return 13;
  39. 	if (number == 'e') 
  40. 		return 14;
  41. 	if (number == 'f') 
  42. 		return 15;
  43. 	return -1;
  44. }
  45.  
  46. std::unordered_map<char, int> table{
  47. 	{ '0', 0 },{ '1', 1 },{ '2', 2 },
  48. 	{ '3', 3 },{ '4', 4 },{ '5', 5 },
  49. 	{ '6', 6 },{ '7', 7 },{ '8', 8 },
  50. 	{ '9', 9 },{ 'a', 10 },{ 'A', 10 },
  51. 	{ 'b', 11 },{ 'B', 11 },{ 'c', 12 },
  52. 	{ 'C', 12 },{ 'd', 13 },{ 'D', 13 },
  53. 	{ 'e', 14 },{ 'E', 14 },{ 'f', 15 },
  54. 	{ 'F', 15 },{ 'x', 0 },{ 'X', 0 } };
  55.  
  56. int hextoint2 (char number)
  57. {
  58. 	return table[(std::size_t)number];
  59. }
  60.  
  61.  
  62. int hextoint4(char number)
  63. {
  64. 	if (number >= '0' && number <= '9')
  65. 		return number - '0';
  66. 	else if (number >= 'a' && number <= 'f')
  67. 		return number - 'a' + 0x0a;
  68. 	else return -1;
  69. }
  70.  
  71. struct Mytable {
  72. 	int x[128];
  73. 	Mytable() : x{}
  74. 	{
  75. 		fill(begin(x), end(x), -1); 
  76. 		for (int i = '0'; i <= '9'; i++)
  77. 			x[i] = i - '0';  
  78. 		for (int i = 'A'; i <= 'F'; i++)
  79. 			x[i] = x[i-'A'+'a'] = i - 'A'+0xa;
  80. 	}
  81. };
  82.  
  83. int hextoint5(char number)
  84. {
  85. 	static Mytable mytable;
  86. 	return  (number < 0 || number>128) ? -1 : mytable.x[number];
  87. }
  88.  
  89. int hextoint6(char number)
  90. {
  91. 	switch (number) {
  92. 	case '0': return 0;
  93. 	case '1': return 1;
  94. 	case '2': return 2;
  95. 	case '3': return 3;
  96. 	case '4': return 4;
  97. 	case '5': return 5;
  98. 	case '6': return 6;
  99. 	case '7': return 7;
  100. 	case '8': return 8;
  101. 	case '9': return 9;
  102. 	case 'A': case 'a': return 0xa;
  103. 	case 'B': case 'b': return 0xb;
  104. 	case 'C': case 'c': return 0xc;
  105. 	case 'D': case 'd': return 0xd;
  106. 	case 'E': case 'e': return 0xe;
  107. 	case 'F': case 'f': return 0xf;
  108. 	default: return - 1;
  109. 	}
  110. }
  111.  
  112. const int variants = 5; 
  113. const long long maxloop = 10000000; 
  114. struct Bench {
  115. 	int(*f)(char); 
  116. 	char *s; 
  117. } bench[variants] = {
  118. 	hextoint1, "If chain                ",
  119. 	hextoint2, "Map(no error processing)",
  120. 	hextoint4, "Compact if              ",
  121. 	hextoint5, "Table based             ",
  122. 	hextoint6, "Switch                  ",
  123. };
  124.  
  125. int main()
  126. {
  127. 	mt19937 generator;
  128. 	std::uniform_int_distribution<int> myrandom(0, 16); 
  129. 	const char *s = "0123456789abcdef";
  130. 	volatile int x;
  131.  
  132. 	for (int i = 0; i < variants; i++) {
  133. 		cout << bench[i].s<<" "; 
  134. 		chrono::high_resolution_clock::time_point t1 = chrono::high_resolution_clock::now(); 
  135. 		for (long long j = 0; j < maxloop; j++) {
  136. 			char c = s[myrandom(generator)];
  137. 			x = bench[i].f(c); 
  138. 		}
  139. 		chrono::high_resolution_clock::time_point t2 = chrono::high_resolution_clock::now();
  140. 		long dt = chrono::duration_cast<chrono::milliseconds>(t2 - t1).count(); 
  141. 		cout << dt << " ms for " << maxloop << " iterations = " << dt * 1000000 / maxloop << " ns/it" << endl; 
  142. 	}
  143. 	cin.get(); 
  144. }
Success #stdin #stdout 1.61s 3464KB
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stdin
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Standard input is empty
stdout
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If chain                 353 ms for 10000000 iterations = 35 ns/it
Map(no error processing) 477 ms for 10000000 iterations = 47 ns/it
Compact if               284 ms for 10000000 iterations = 28 ns/it
Table based              241 ms for 10000000 iterations = 24 ns/it
Switch                   264 ms for 10000000 iterations = 26 ns/it
https://ideone.com/RrgKhd
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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