eccodes/src/grib_iterator_class_gaussian.c

/*
 * (C) Copyright 2005- ECMWF.
 *
 * This software is licensed under the terms of the Apache Licence Version 2.0
 * which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
 *
 * In applying this licence, ECMWF does not waive the privileges and immunities granted to it by
 * virtue of its status as an intergovernmental organisation nor does it submit to any jurisdiction.
 */
/**************************************
 *  Enrico Fucile
 **************************************/


#include "grib_api_internal.h"
#include <math.h>

/*
   This is used by make_class.pl

   START_CLASS_DEF
   CLASS      = iterator
   SUPER      = grib_iterator_class_regular
   IMPLEMENTS = init
   END_CLASS_DEF

 */

/* START_CLASS_IMP */

/*

Don't edit anything between START_CLASS_IMP and END_CLASS_IMP
Instead edit values between START_CLASS_DEF and END_CLASS_DEF
or edit "iterator.class" and rerun ./make_class.pl

*/


static void init_class(grib_iterator_class*);

static int init(grib_iterator* i, grib_handle*, grib_arguments*);


typedef struct grib_iterator_gaussian
{
    grib_iterator it;
    /* Members defined in gen */
    long carg;
    const char* missingValue;
    /* Members defined in regular */
    double* las;
    double* los;
    long Ni;
    long Nj;
    long iScansNegatively;
    long isRotated;
    double angleOfRotation;
    double southPoleLat;
    double southPoleLon;
    long jPointsAreConsecutive;
    long disableUnrotate;
    /* Members defined in gaussian */
} grib_iterator_gaussian;

extern grib_iterator_class* grib_iterator_class_regular;

static grib_iterator_class _grib_iterator_class_gaussian = {
    &grib_iterator_class_regular,   /* super                     */
    "gaussian",                     /* name                      */
    sizeof(grib_iterator_gaussian), /* size of instance          */
    0,                              /* inited */
    &init_class,                    /* init_class */
    &init,                          /* constructor               */
    0,                              /* destructor                */
    0,                              /* Next Value                */
    0,                              /*  Previous Value           */
    0,                              /* Reset the counter         */
    0,                              /* has next values           */
};

grib_iterator_class* grib_iterator_class_gaussian = &_grib_iterator_class_gaussian;


static void init_class(grib_iterator_class* c)
{
    c->next     = (*(c->super))->next;
    c->previous = (*(c->super))->previous;
    c->reset    = (*(c->super))->reset;
    c->has_next = (*(c->super))->has_next;
}
/* END_CLASS_IMP */

static void binary_search(double xx[], const unsigned long n, double x, unsigned long* j);

static int init(grib_iterator* i, grib_handle* h, grib_arguments* args)
{
    grib_iterator_gaussian* self = (grib_iterator_gaussian*)i;

    double* lats;
    double laf; /* latitude of first point in degrees */
    double lal; /* latitude of last point in degrees */
    long trunc; /* number of parallels between a pole and the equator */
    long lai;
    long jScansPositively = 0;
    int size;
    double start;
    unsigned long istart = 0;
    int ret              = GRIB_SUCCESS;

    const char* latofirst          = grib_arguments_get_name(h, args, self->carg++);
    const char* latoflast          = grib_arguments_get_name(h, args, self->carg++);
    const char* numtrunc           = grib_arguments_get_name(h, args, self->carg++);
    const char* s_jScansPositively = grib_arguments_get_name(h, args, self->carg++);

    if ((ret = grib_get_double_internal(h, latofirst, &laf)))
        return ret;
    if ((ret = grib_get_double_internal(h, latoflast, &lal)))
        return ret;
    if ((ret = grib_get_long_internal(h, numtrunc, &trunc)))
        return ret;
    if ((ret = grib_get_long_internal(h, s_jScansPositively, &jScansPositively)))
        return ret;

    start = laf;

    size = trunc * 2;

    lats = (double*)grib_context_malloc(h->context, size * sizeof(double));

    ret = grib_get_gaussian_latitudes(trunc, lats);

    if (ret != GRIB_SUCCESS) {
        grib_context_log(h->context, GRIB_LOG_ERROR, "error %d calculating gaussian points", ret);
        return ret;
    }
    /*
  for(loi=(trunc*2)-1;loi>=0;loi--)
    if(fabs(lats[loi] - lal) < glatPrecision) break;
  for(j=(trunc*2)-1;j>0;j--) {
    if(fabs(lats[j] - laf) < glatPrecision) break;
  }
     */

    binary_search(lats, size - 1, start, &istart);
    Assert(istart < size);

    if (jScansPositively) {
        for (lai = 0; lai < self->Nj; lai++) {
            self->las[lai] = lats[istart--];
            /*if (istart<0) istart=size-1;  this condition is always FALSE -- 'istart' is unsigned long */
        }
    }
    else {
        for (lai = 0; lai < self->Nj; lai++) {
            self->las[lai] = lats[istart++];
            if (istart > size - 1)
                istart = 0;
        }
    }

    grib_context_free(h->context, lats);

    return ret;
}

static void binary_search(double xx[], const unsigned long n, double x, unsigned long* j)
{
    /*This routine works only on descending ordered arrays*/
#define EPSILON 1e-3

    unsigned long ju, jm, jl;
    jl = 0;
    ju = n;
    while (ju - jl > 1) {
        jm = (ju + jl) >> 1;
        if (fabs(x - xx[jm]) < EPSILON) {
            /* found something close enough. We're done */
            *j = jm;
            return;
        }
        if (x < xx[jm])
            jl = jm;
        else
            ju = jm;
    }
    *j = jl;
}