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- #include <math.h>
- #include <stdbool.h>
- double floor(double x)
- {
- return (double) (x < 0.f ? ((int) x == x ? x : (((int) x) - 1)) : ((int) x));
- }
- #define MAXEXP 2031 /* (MAX_EXP * 16) - 1 */
- #define MINEXP -2047 /* (MIN_EXP * 16) - 1 */
- #define HUGE MAXFLOAT
- static const double a1[] =
- {
- 1.0,
- 0.95760328069857365,
- 0.91700404320467123,
- 0.87812608018664974,
- 0.84089641525371454,
- 0.80524516597462716,
- 0.77110541270397041,
- 0.73841307296974966,
- 0.70710678118654752,
- 0.67712777346844637,
- 0.64841977732550483,
- 0.62092890603674203,
- 0.59460355750136054,
- 0.56939431737834583,
- 0.54525386633262883,
- 0.52213689121370692,
- 0.50000000000000000
- };
- static const double a2[] =
- {
- 0.24114209503420288E-17,
- 0.92291566937243079E-18,
- -0.15241915231122319E-17,
- -0.35421849765286817E-17,
- -0.31286215245415074E-17,
- -0.44654376565694490E-17,
- 0.29306999570789681E-17,
- 0.11260851040933474E-17
- };
- static const double
- p1 = 0.833333333333332114e-1,
- p2 = 0.125000000005037992e-1,
- p3 = 0.223214212859242590e-2,
- p4 = 0.434457756721631196e-3,
- q1 = 0.693147180559945296e0,
- q2 = 0.240226506959095371e0,
- q3 = 0.555041086640855953e-1,
- q4 = 0.961812905951724170e-2,
- q5 = 0.133335413135857847e-2,
- q6 = 0.154002904409897646e-3,
- q7 = 0.149288526805956082e-4,
- k = 0.442695040888963407;
- double pow(double x, double y)
- {
- double frexp(), g, ldexp(), r, u1, u2, v, w, w1, w2, y1, y2, z;
- int iw1, m, p;
- bool flipsignal = false;
- if (y == 0.0)
- return (1.0);
- if (x <= 0.0)
- {
- if (x == 0.0)
- {
- if (y > 0.0)
- return 0.0;
- //cmemsg(FP_POWO, &y);
- //return(HUGE);
- }
- else
- {
- //cmemsg(FP_POWN, &x);
- x = -x;
- if (y != (int) y) { // if y is fractional, then this woud result in a complex number
- return NAN;
- }
- flipsignal = ((int) y) & 1;
- }
- }
- g = frexp(x, &m);
- p = 0;
- if (g <= a1[8])
- p = 8;
- if (g <= a1[p + 4])
- p += 4;
- if (g <= a1[p + 2])
- p += 2;
- p++;
- z = ((g - a1[p]) - a2[p / 2]) / (g + a1[p]);
- z += z;
- v = z * z;
- r = (((p4 * v + p3) * v + p2) * v + p1) * v * z;
- r += k * r;
- u2 = (r + z * k) + z;
- u1 = 0.0625 * (double)(16 * m - p);
- y1 = 0.0625 * (double)((int)(16.0 * y));
- y2 = y - y1;
- w = u2 * y + u1 * y2;
- w1 = 0.0625 * (double)((int)(16.0 * w));
- w2 = w - w1;
- w = w1 + u1 * y1;
- w1 = 0.0625 * (double)((int)(16.0 * w));
- w2 += (w - w1);
- w = 0.0625 * (double)((int)(16.0 * w2));
- iw1 = 16.0 * (w1 + w);
- w2 -= w;
- while (w2 > 0.0)
- {
- iw1++;
- w2 -= 0.0625;
- }
- if (iw1 > MAXEXP)
- {
- //cmemsg(FP_POWO, &y);
- return (HUGE);
- }
- if (iw1 < MINEXP)
- {
- //cmemsg(FP_POWU, &y);
- return (0.0);
- }
- m = iw1 / 16;
- if (iw1 >= 0)
- m++;
- p = 16 * m - iw1;
- z = ((((((q7 * w2 + q6) * w2 + q5) * w2 + q4) * w2 + q3) * w2 + q2) * w2 + q1) * w2;
- z = a1[p] + a1[p] * z;
- double res = ldexp(z, m);
- return flipsignal ? -res : res;
- }
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