math.c 3.2 KB

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  1. #include <math.h>
  2. #include <stdbool.h>
  3. double floor(double x)
  4. {
  5. return (double) (x < 0.f ? ((int) x == x ? x : (((int) x) - 1)) : ((int) x));
  6. }
  7. #define MAXEXP 2031 /* (MAX_EXP * 16) - 1 */
  8. #define MINEXP -2047 /* (MIN_EXP * 16) - 1 */
  9. #define HUGE MAXFLOAT
  10. static const double a1[] =
  11. {
  12. 1.0,
  13. 0.95760328069857365,
  14. 0.91700404320467123,
  15. 0.87812608018664974,
  16. 0.84089641525371454,
  17. 0.80524516597462716,
  18. 0.77110541270397041,
  19. 0.73841307296974966,
  20. 0.70710678118654752,
  21. 0.67712777346844637,
  22. 0.64841977732550483,
  23. 0.62092890603674203,
  24. 0.59460355750136054,
  25. 0.56939431737834583,
  26. 0.54525386633262883,
  27. 0.52213689121370692,
  28. 0.50000000000000000
  29. };
  30. static const double a2[] =
  31. {
  32. 0.24114209503420288E-17,
  33. 0.92291566937243079E-18,
  34. -0.15241915231122319E-17,
  35. -0.35421849765286817E-17,
  36. -0.31286215245415074E-17,
  37. -0.44654376565694490E-17,
  38. 0.29306999570789681E-17,
  39. 0.11260851040933474E-17
  40. };
  41. static const double
  42. p1 = 0.833333333333332114e-1,
  43. p2 = 0.125000000005037992e-1,
  44. p3 = 0.223214212859242590e-2,
  45. p4 = 0.434457756721631196e-3,
  46. q1 = 0.693147180559945296e0,
  47. q2 = 0.240226506959095371e0,
  48. q3 = 0.555041086640855953e-1,
  49. q4 = 0.961812905951724170e-2,
  50. q5 = 0.133335413135857847e-2,
  51. q6 = 0.154002904409897646e-3,
  52. q7 = 0.149288526805956082e-4,
  53. k = 0.442695040888963407;
  54. double pow(double x, double y)
  55. {
  56. double frexp(), g, ldexp(), r, u1, u2, v, w, w1, w2, y1, y2, z;
  57. int iw1, m, p;
  58. bool flipsignal = false;
  59. if (y == 0.0)
  60. return (1.0);
  61. if (x <= 0.0)
  62. {
  63. if (x == 0.0)
  64. {
  65. if (y > 0.0)
  66. return 0.0;
  67. //cmemsg(FP_POWO, &y);
  68. //return(HUGE);
  69. }
  70. else
  71. {
  72. //cmemsg(FP_POWN, &x);
  73. x = -x;
  74. if (y != (int) y) { // if y is fractional, then this woud result in a complex number
  75. return NAN;
  76. }
  77. flipsignal = ((int) y) & 1;
  78. }
  79. }
  80. g = frexp(x, &m);
  81. p = 0;
  82. if (g <= a1[8])
  83. p = 8;
  84. if (g <= a1[p + 4])
  85. p += 4;
  86. if (g <= a1[p + 2])
  87. p += 2;
  88. p++;
  89. z = ((g - a1[p]) - a2[p / 2]) / (g + a1[p]);
  90. z += z;
  91. v = z * z;
  92. r = (((p4 * v + p3) * v + p2) * v + p1) * v * z;
  93. r += k * r;
  94. u2 = (r + z * k) + z;
  95. u1 = 0.0625 * (double)(16 * m - p);
  96. y1 = 0.0625 * (double)((int)(16.0 * y));
  97. y2 = y - y1;
  98. w = u2 * y + u1 * y2;
  99. w1 = 0.0625 * (double)((int)(16.0 * w));
  100. w2 = w - w1;
  101. w = w1 + u1 * y1;
  102. w1 = 0.0625 * (double)((int)(16.0 * w));
  103. w2 += (w - w1);
  104. w = 0.0625 * (double)((int)(16.0 * w2));
  105. iw1 = 16.0 * (w1 + w);
  106. w2 -= w;
  107. while (w2 > 0.0)
  108. {
  109. iw1++;
  110. w2 -= 0.0625;
  111. }
  112. if (iw1 > MAXEXP)
  113. {
  114. //cmemsg(FP_POWO, &y);
  115. return (HUGE);
  116. }
  117. if (iw1 < MINEXP)
  118. {
  119. //cmemsg(FP_POWU, &y);
  120. return (0.0);
  121. }
  122. m = iw1 / 16;
  123. if (iw1 >= 0)
  124. m++;
  125. p = 16 * m - iw1;
  126. z = ((((((q7 * w2 + q6) * w2 + q5) * w2 + q4) * w2 + q3) * w2 + q2) * w2 + q1) * w2;
  127. z = a1[p] + a1[p] * z;
  128. double res = ldexp(z, m);
  129. return flipsignal ? -res : res;
  130. }