mirror of https://github.com/XEphem/XEphem.git
208 lines
6.0 KiB
C
208 lines
6.0 KiB
C
/* VSOP87 planetary theory
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*
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* currently uses version VSOP87D:
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* heliocentric spherical, mean ecliptic of date.
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*
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* calculation of rates (daily changes) is optional;
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* see header file for the necessary #define's
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*
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* rough orientation on calculation time, miliseconds
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* on an HP 715/75, all planets Mercury to Neptune, prec=0.0:
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*
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* terms with rates without rates
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* 3598 11 7.1
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* 31577 51 44
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*
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* with secular terms for JD 2232395.0 19/12/1399 0h TDB:
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*
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* FULL PRECISION code (31577 terms), milliseconds
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* prec terms rates no rates
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* 1e-8 15086 62 36
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* 1e-7 10105 44 25
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* 1e-6 3725 20 13
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* 1e-5 1324 11 7.8
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* 1e-4 443 7.0 6.0
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* 1e-3 139 6.0 5.0
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*
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* REDUCED PRECISION code (3598 terms), milliseconds
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* prec terms rates no rates
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* 1e-7 2463 9.9 5.5
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* 1e-6 1939 8.0 4.5
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* 1e-5 1131 4.9 2.9
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* 1e-4 443 2.2 1.5
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* 1e-3 139 1.0 0.9
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*/
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#include <math.h>
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#include "astro.h"
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#include "vsop87.h"
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#define VSOP_A1000 365250.0 /* days per millenium */
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#define VSOP_MAXALPHA 5 /* max degree of time */
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/******************************************************************
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* adapted from BdL FORTRAN Code; stern
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*
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* Reference : Bureau des Longitudes - PBGF9502
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*
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* Object : calculate a VSOP87 position for a given time.
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*
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* Input :
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*
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* mj modified julian date, counted from J1900.0
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* time scale : dynamical time TDB.
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*
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* obj object number as in astro.h, NB: not for pluto
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*
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* prec relative precision
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*
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* if prec is equal to 0 then the precision is the precision
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* p0 of the complete solution VSOP87.
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* Mercury p0 = 0.6 10**-8
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* Venus p0 = 2.5 10**-8
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* Earth p0 = 2.5 10**-8
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* Mars p0 = 10.0 10**-8
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* Jupiter p0 = 35.0 10**-8
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* Saturn p0 = 70.0 10**-8
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* Uranus p0 = 8.0 10**-8
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* Neptune p0 = 42.0 10**-8
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*
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* if prec is not equal to 0, let us say in between p0 and
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* 10**-3, the precision is :
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* for the positions :
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* - prec*a0 au for the distances.
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* - prec rad for the other variables.
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* for the velocities :
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* - prec*a0 au/day for the distances.
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* - prec rad/day for the other variables.
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* a0 is the semi-major axis of the body.
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*
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* Output :
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*
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* ret[6] array of the results (double).
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*
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* for spherical coordinates :
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* 1: longitude (rd)
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* 2: latitude (rd)
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* 3: radius (au)
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* #if VSOP_GETRATE:
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* 4: longitude velocity (rad/day)
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* 5: latitude velocity (rad/day)
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* 6: radius velocity (au/day)
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*
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* return: error index (int)
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* 0: no error.
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* 2: object out of range [MERCURY .. NEPTUNE, SUN]
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* 3: precision out of range [0.0 .. 1e-3]
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******************************************************************/
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int
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vsop87 (double mj, int obj, double prec, double *ret)
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{
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static double (*vx_map[])[3] = { /* data tables */
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vx_mercury, vx_venus, vx_mars, vx_jupiter,
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vx_saturn, vx_uranus, vx_neptune, 0, vx_earth,
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};
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static int (*vn_map[])[3] = { /* indexes */
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vn_mercury, vn_venus, vn_mars, vn_jupiter,
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vn_saturn, vn_uranus, vn_neptune, 0, vn_earth,
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};
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static double a0[] = { /* semimajor axes; for precision ctrl only */
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0.39, 0.72, 1.5, 5.2, 9.6, 19.2, 30.1, 39.5, 1.0,
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};
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double (*vx_obj)[3] = vx_map[obj]; /* VSOP87 data and indexes */
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int (*vn_obj)[3] = vn_map[obj];
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double t[VSOP_MAXALPHA+1]; /* powers of time */
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double t_abs[VSOP_MAXALPHA+1]; /* powers of abs(time) */
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double q; /* aux for precision control */
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int i, cooidx, alpha; /* misc indexes */
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if (obj == PLUTO || obj > SUN)
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return (2);
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if (prec < 0.0 || prec > 1e-3)
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return(3);
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/* zero result array */
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for (i = 0; i < 6; ++i) ret[i] = 0.0;
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/* time and its powers */
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t[0] = 1.0;
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t[1] = (mj - J2000)/VSOP_A1000;
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for (i = 2; i <= VSOP_MAXALPHA; ++i) t[i] = t[i-1] * t[1];
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t_abs[0] = 1.0;
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for (i = 1; i <= VSOP_MAXALPHA; ++i) t_abs[i] = fabs(t[i]);
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/* precision control */
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q = -log10(prec + 1e-35) - 2; /* decades below 1e-2 */
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q = VSOP_ASCALE * prec / 10.0 / q; /* reduce threshold progressively
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* for higher precision */
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/* do the term summation; first the spatial dimensions */
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for (cooidx = 0; cooidx < 3; ++cooidx) {
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/* then the powers of time */
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for (alpha = 0; vn_obj[alpha+1][cooidx] ; ++alpha) {
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double p, term, termdot;
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/* precision threshold */
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p= alpha ? q/(t_abs[alpha] + alpha*t_abs[alpha-1]*1e-4 + 1e-35) : q;
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#if VSOP_SPHERICAL
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if (cooidx == 2) /* scale by semimajor axis for radius */
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#endif
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p *= a0[obj];
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term = termdot = 0.0;
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for (i = vn_obj[alpha][cooidx]; i < vn_obj[alpha+1][cooidx]; ++i) {
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double a, b, c, arg;
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a = vx_obj[i][0];
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if (a < p) continue; /* ignore small terms */
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b = vx_obj[i][1];
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c = vx_obj[i][2];
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arg = b + c * t[1];
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term += a * cos(arg);
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#if VSOP_GETRATE
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termdot += -c * a * sin(arg);
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#endif
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}
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ret[cooidx] += t[alpha] * term;
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#if VSOP_GETRATE
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ret[cooidx + 3] += t[alpha] * termdot +
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((alpha > 0) ? alpha * t[alpha - 1] * term : 0.0);
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#endif
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} /* alpha */
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} /* cooidx */
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for (i = 0; i < 6; ++i) ret[i] /= VSOP_ASCALE;
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#if VSOP_SPHERICAL
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/* reduce longitude to 0..2pi */
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ret[0] -= floor(ret[0]/(2.*PI)) * (2.*PI);
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#endif
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#if VSOP_GETRATE
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/* convert millenium rate to day rate */
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for (i = 3; i < 6; ++i) ret[i] /= VSOP_A1000;
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#endif
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#if VSOP_SPHERICAL
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/* reduction from dynamical equinox of VSOP87 to FK5;
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*/
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if (prec < 5e-7) { /* 5e-7 rad = 0.1 arc seconds */
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double L1, c1, s1;
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L1 = ret[0] - degrad(13.97 * t[1] - 0.031 * t[2]);
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c1 = cos(L1); s1 = sin(L1);
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ret[0] += degrad(-0.09033 + 0.03916 * (c1 + s1) * tan(ret[1]))/3600.0;
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ret[1] += degrad(0.03916 * (c1 - s1))/3600.0;
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}
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#endif
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return (0);
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}
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