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  1. // 2^(expn2)を有効数字disp10桁の10進数で指数表示する。
  2. // Usage: print_by_decimal <expn2> <disp10>
  3. #include <stdio.h>
  4. #include <stdlib.h>
  5. #include <stdint.h>
  6. #include <assert.h>
  7. #include <vector>
  8. #include <utility>
  9.  
  10. #include <time.h>
  11.  
  12. // 指数の型
  13. typedef int64_t expn_t;
  14.  
  15. // 上の桁の10の剰余を繰り込んでもuint32_tが桁あふれしない最大のビット数
  16. #define DIGIT_BITS	27
  17.  
  18. static_assert(UINT32_MAX / 9UL >= (1UL << DIGIT_BITS), "*** ERR ***");
  19. static_assert((9UL << DIGIT_BITS) + ((1UL << DIGIT_BITS) - 1UL) <= UINT32_MAX, "*** ERR ***");
  20.  
  21. // 除数定義
  22. // 除数は10で固定する。
  23. // DIGIT_BITSを10で割る用に最適化しているので一般化困難。
  24. const int DIVISOR = 10;
  25.  
  26. namespace
  27. {
  28. 	uint32_t div_by_10(uint32_t mbuf[], const size_t sz_, uint32_t& ulNonZeroBits, expn_t& progress)
  29. 	{
  30. 		// 出力パラメータ初期化
  31. 		ulNonZeroBits = 0UL;
  32. 		progress = 0;
  33.  
  34. 		// 冒頭の0をスキップ
  35. 		// スキップできた個数が進捗でもある。
  36. 		size_t sz = sz_;
  37. 		while (sz > 0 && mbuf[sz - 1] == 0UL) {
  38. 			progress++;
  39. 			sz--;
  40. 		}
  41.  
  42. 		// 最初の非0要素以降を処理
  43. 		uint32_t remain = 0UL;
  44. 		for (size_t i = sz; i > 0; i--) {
  45. 			const long dividend = (remain << DIGIT_BITS) + mbuf[i - 1];
  46. 			ulNonZeroBits |= dividend;
  47. 			const long quotient = dividend / DIVISOR;
  48. 			remain = dividend - quotient * DIVISOR;
  49. 			assert(0 <= remain && remain < 10);
  50. 			mbuf[i - 1] = quotient;
  51. 		}
  52.  
  53. 		return remain;
  54. 	}
  55.  
  56. }	// namespace
  57.  
  58. int main(const int argc, char* argv[])
  59. {
  60. 	// 2のべきの指数
  61. 	//expn_t expn2 = 17179869183;		// 0.000001% / 113秒
  62. 	expn_t expn2 = 1000;
  63. 	//expn_t expn2 = 64;
  64. 	//expn_t expn2 = 32;
  65. 	//expn_t expn2 = 16;
  66. 	//expn_t expn2 = 8;
  67. 	//expn_t expn2 = 0;
  68.  
  69. 	// 表示桁数(有効数字)
  70. 	expn_t disp10 = 64;
  71.  
  72. #ifdef _WIN32
  73. 	if (argc >= 2) {
  74. 		expn2 = _atoi64(argv[1]);
  75. 	}
  76. 	if (argc >= 3) {
  77. 		disp10 = _atoi64(argv[2]);
  78. 	}
  79. #else
  80. 	(void)(argc, argv);
  81. #endif
  82.  
  83. 	// 2^(expn2)のバッファ確保
  84. 	const size_t sz = (size_t)expn2 / (size_t)DIGIT_BITS + (size_t)1;
  85. 	std::vector<uint32_t> mbuf(sz, 0L);
  86.  
  87. 	// 2^(expn2)代入
  88. 	mbuf[sz - 1] = 1L << ((size_t)expn2 - (size_t)DIGIT_BITS * (sz - 1));
  89.  
  90. 	// 桁バッファ確保
  91. 	std::vector<uint8_t> decimals((size_t)disp10);
  92.  
  93. 	// 10進数の下の桁から順次取得
  94. 	// 被除数が0になるまで10でひたすら割り続ける。
  95. 	expn_t expn10 = 0;
  96. 	expn_t idx = 0;
  97. 	const time_t startTmg = time(NULL);
  98. 	time_t prevTmg = startTmg;
  99. 	for (;;) {
  100. 		// 10で割る
  101. 		uint32_t ulNonZeroBits;
  102. 		expn_t progress;
  103. 		const uint32_t remain = div_by_10(&(mbuf[0]), sz, ulNonZeroBits, progress);
  104. 		assert(0 <= remain && remain < 10);
  105.  
  106. 		// 進捗表示
  107. 		const time_t now = time(NULL);
  108. 		fprintf(stderr, "[%lld] %f %% (%lld/%zu) --- %lld sec\r",
  109. 			expn10, 100.0 * (double)progress / (double)sz, progress, sz, now - startTmg);
  110. 		if (now != prevTmg) {
  111. 			fprintf(stderr, "\n");
  112. 			prevTmg = now;
  113. 		}
  114.  
  115. 		// 修了判定
  116. 		if (ulNonZeroBits == 0UL) {
  117. 			// (被除数が0になった)
  118. 			assert(remain == 0UL);
  119. 			expn10--;
  120. 			break;
  121. 		}
  122.  
  123. 		// 桁を記憶
  124. 		if (idx >= disp10) {
  125. 			idx = 0;
  126. 		}
  127. 		decimals[idx++] = (uint8_t)remain;
  128. 		expn10++;
  129. 	}
  130. 	fprintf(stderr, "\n");
  131.  
  132. 	// 表示
  133. 	printf("2^%lld = ", expn2);
  134. 	const expn_t ndisp = std::min(disp10, expn10 + 1);
  135. 	if (ndisp <= 1) {
  136. 		printf("%d", decimals[--idx]);
  137. 	}
  138. 	else {
  139. 		printf("%d.", decimals[--idx]);
  140. 		for (expn_t i = 1; i < ndisp; i++) {
  141. 			if (idx <= 0) {
  142. 				idx = disp10;
  143. 			}
  144. 			printf("%d", decimals[--idx]);
  145. 		}
  146. 		printf(" x 10^%lld\n", expn10);
  147. 	}
  148. }
  149.  
Success #stdin #stdout #stderr 0.01s 5316KB
comments (?)
stdin 
Standard input is empty
stdout 
2^1000 = 1.071508607186267320948425049060001810561404811705533607443750388 x 10^301
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https://ideone.com/6BG7hf
language:
C++14 (clang 8.0)
created:
3 years ago
visibility:
public

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