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/* Determine nad table correction value */
#define PJ_LIB__
#include <projects.h>
LP
nad_intr(LP t, struct CTABLE *ct) {
LP val, frct;
ILP indx;
double m00, m10, m01, m11;
FLP *f00, *f10, *f01, *f11;
long index;
int in;
indx.lam = floor(t.lam /= ct->del.lam);
indx.phi = floor(t.phi /= ct->del.phi);
frct.lam = t.lam - indx.lam;
frct.phi = t.phi - indx.phi;
val.lam = val.phi = HUGE_VAL;
if (indx.lam < 0) {
if (indx.lam == -1 && frct.lam > 0.99999999999) {
++indx.lam;
frct.lam = 0.;
} else
return val;
} else if ((in = indx.lam + 1) >= ct->lim.lam) {
if (in == ct->lim.lam && frct.lam < 1e-11) {
--indx.lam;
frct.lam = 1.;
} else
return val;
}
if (indx.phi < 0) {
if (indx.phi == -1 && frct.phi > 0.99999999999) {
++indx.phi;
frct.phi = 0.;
} else
return val;
} else if ((in = indx.phi + 1) >= ct->lim.phi) {
if (in == ct->lim.phi && frct.phi < 1e-11) {
--indx.phi;
frct.phi = 1.;
} else
return val;
}
index = indx.phi * ct->lim.lam + indx.lam;
f00 = ct->cvs + index++;
f10 = ct->cvs + index;
index += ct->lim.lam;
f11 = ct->cvs + index--;
f01 = ct->cvs + index;
m11 = m10 = frct.lam;
m00 = m01 = 1. - frct.lam;
m11 *= frct.phi;
m01 *= frct.phi;
frct.phi = 1. - frct.phi;
m00 *= frct.phi;
m10 *= frct.phi;
val.lam = m00 * f00->lam + m10 * f10->lam +
m01 * f01->lam + m11 * f11->lam;
val.phi = m00 * f00->phi + m10 * f10->phi +
m01 * f01->phi + m11 * f11->phi;
return val;
}
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