cell_stats.c

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/*!
 * \file lib/raster/cell_stats.c
 *
 * \brief Raster Library - Raster cell statistics
 *
 * SPDX-FileCopyrightText: 2001-2009 GRASS Development Team
 * SPDX-License-Identifier: GPL-2.0-or-later
 *
 * \author Original author CERL
 */
 
#include <stdlib.h>
 
#include <grass/gis.h>
#include <grass/raster.h>
 
#define INCR  10
#define SHIFT 6
 
static const int NCATS = 1 << SHIFT;
 
#define NODE struct Cell_stats_node
 
static int next_node(struct Cell_stats *);
static void init_node(NODE *, int, int);
 
/*!
 * \brief Initialize cell stats
 *
 * This routine, which must be called first, initializes the
 * Cell_stats structure.
 *
 * Set the count for NULL-values to zero.
 *
 * \param s pointer to Cell_stats structure
 */
void Rast_init_cell_stats(struct Cell_stats *s)
{
    s->N = 0;
    s->tlen = INCR;
    s->node = (NODE *)G_malloc(s->tlen * sizeof(NODE));
    s->null_data_count = 0;
}
 
/*!
 * \brief Add data to cell stats
 *
 * The <i>n</i> CELL values in the <i>data</i> array are inserted (and
 * counted) in the Cell_stats structure.
 *
 * Look for NULLs and update the NULL-value count.
 *
 * \param cell raster values
 * \param n number of values
 * \param s pointer to Cell_stats structure which holds cell stats info
 *
 * \return 1 on failure
 * \return 0 on success
 */
int Rast_update_cell_stats(const CELL *cell, int n, struct Cell_stats *s)
{
    CELL cat;
    int p, q;
    int idx, offset;
    int N;
    NODE *node, *pnode;
    NODE *new_node;
 
    if (n <= 0)
        return 1;
 
    node = s->node;
 
    /* first non-null node is special case */
    if ((N = s->N) == 0) {
        cat = *cell++;
        while (Rast_is_c_null_value(&cat)) {
            s->null_data_count++;
            cat = *cell++;
            n--;
        }
        if (n > 0) { /* if there are some non-null cells */
            N = 1;
            if (cat < 0) {
                idx = -((-cat) >> SHIFT) - 1;
                offset = cat + ((-idx) << SHIFT) - 1;
            }
            else {
                idx = cat >> SHIFT;
                offset = cat - (idx << SHIFT);
            }
            fflush(stderr);
            init_node(&node[1], idx, offset);
            node[1].right = 0;
            n--;
        }
    }
    while (n-- > 0) {
        cat = *cell++;
        if (Rast_is_c_null_value(&cat)) {
            s->null_data_count++;
            continue;
        }
        if (cat < 0) {
            idx = -((-cat) >> SHIFT) - 1;
            offset = cat + ((-idx) << SHIFT) - 1;
        }
        else {
            idx = cat >> SHIFT;
            offset = cat - (idx << SHIFT);
        }
 
        q = 1;
        while (q > 0) {
            pnode = &node[p = q];
            if (pnode->idx == idx) {
                pnode->count[offset]++;
                break;
            }
            if (pnode->idx > idx)
                q = pnode->left; /* go left */
            else
                q = pnode->right; /* go right */
        }
        if (q > 0)
            continue; /* found */
 
        /* new node */
        N++;
 
        /* grow the tree? */
        if (N >= s->tlen) {
            node = (NODE *)G_realloc((char *)node,
                                     sizeof(NODE) * (s->tlen += INCR));
            pnode = &node[p]; /* realloc moves node, must reassign pnode */
        }
 
        /* add node to tree */
        init_node(new_node = &node[N], idx, offset);
 
        if (pnode->idx > idx) {
            new_node->right = -p; /* create thread */
            pnode->left = N;      /* insert left */
        }
        else {
            new_node->right = pnode->right; /* copy right link/thread */
            pnode->right = N;               /* add right */
        }
    } /* while n-- > 0 */
    s->N = N;
    s->node = node;
 
    return 0;
}
 
static void init_node(NODE *node, int idx, int offset)
{
    long *count;
    int i;
 
    count = node->count = (long *)G_calloc(i = NCATS, sizeof(long));
    while (i--)
        *count++ = 0;
    node->idx = idx;
    node->count[offset] = 1;
    node->left = 0;
}
 
/*!
 * \brief Random query of cell stats
 *
 * This routine allows a random query of the Cell_stats structure. The
 * \p count associated with the raster value \p cat is
 * set. The routine returns 1 if \p cat was found in the
 * structure, 0 otherwise.
 *
 * Allow finding the count for the NULL-value.
 *
 * \param cat raster value
 * \param[out] count count
 * \param s pointer to Cell_stats structure which holds cell stats info
 *
 * \return 1 if found
 * \return 0 if not found
 */
int Rast_find_cell_stat(CELL cat, long *count, const struct Cell_stats *s)
{
    int q;
    int idx;
    int offset;
 
    *count = 0;
    if (Rast_is_c_null_value(&cat)) {
        *count = s->null_data_count;
        return (*count != 0);
    }
 
    if (s->N <= 0)
        return 0;
 
    /*
       if (cat < 0)
       {
       idx = -(-cat/NCATS) - 1;
       offset = cat - idx*NCATS - 1;
       }
       else
       {
       idx = cat/NCATS;
       offset = cat - idx*NCATS;
       }
     */
    if (cat < 0) {
        idx = -((-cat) >> SHIFT) - 1;
        offset = cat + ((-idx) << SHIFT) - 1;
    }
    else {
        idx = cat >> SHIFT;
        offset = cat - (idx << SHIFT);
    }
 
    q = 1;
    while (q > 0) {
        if (s->node[q].idx == idx) {
            *count = s->node[q].count[offset];
            return (*count != 0);
        }
        if (s->node[q].idx > idx)
            q = s->node[q].left; /* go left */
        else
            q = s->node[q].right; /* go right */
    }
    return 0;
}
 
/*!
 * \brief Reset/rewind cell stats
 *
 * The structure <i>s</i> is rewound (i.e., positioned at the first
 * raster category) so that sorted sequential retrieval can begin.
 *
 * \param s pointer to Cell_stats structure which holds cell stats info
 *
 * \return 0
 */
int Rast_rewind_cell_stats(struct Cell_stats *s)
{
    int q;
 
    if (s->N <= 0)
        return 1;
    /* start at root and go all the way to the left */
    s->curp = 1;
    while ((q = s->node[s->curp].left))
        s->curp = q;
    s->curoffset = -1;
 
    return 0;
}
 
static int next_node(struct Cell_stats *s)
{
    int q;
 
    /* go to the right */
    s->curp = s->node[s->curp].right;
 
    if (s->curp == 0) /* no more */
        return 0;
 
    if (s->curp < 0) { /* thread. stop here */
        s->curp = -(s->curp);
        return 1;
    }
 
    while ((q = s->node[s->curp].left)) /* now go all the way left */
        s->curp = q;
 
    return 1;
}
 
/*!
 * \brief Retrieve sorted cell stats
 *
 * Retrieves the next <i>cat, count</i> combination from the
 * structure. Returns 0 if there are no more items, non-zero if there
 * are more. For example:
 *
 \code
 struct Cell_stats s;
 CELL cat;
 long count;
 
 // updating <b>s</b> occurs here
 
 Rast_rewind_cell_stats(&s);
 while (Rast_next_cell_stat(&cat,&count,&s)
 fprintf(stdout, "%ld %ld\n", (long) cat, count);
 \endcode
 *
 * Do not return a record for the NULL-value
 *
 * \param cat raster value
 * \param[out] count
 * \param s pointer to Cell_stats structure which holds cell stats info
 *
 * \return 0 if there are no more items
 * \return non-zero if there are more
 */
int Rast_next_cell_stat(CELL *cat, long *count, struct Cell_stats *s)
{
    int idx;
 
    /* first time report stats for null */
    /* decided not to return stats for null in this function
       static int null_reported = 0;
       if(!null_reported && s->null_data_count > 0)
       {
       *count = s->null_data_count;
       Rast_set_c_null_value(&cat,1);
       null_reported = 1;
       return 1;
       }
     */
    if (s->N <= 0)
        return 0;
    for (;;) {
        s->curoffset++;
        if (s->curoffset >= NCATS) {
            if (!next_node(s))
                return 0;
            s->curoffset = -1;
            continue;
        }
        if ((*count = s->node[s->curp].count[s->curoffset])) {
            idx = s->node[s->curp].idx;
 
            /*
               if (idx < 0)
               *cat = idx*NCATS + s->curoffset+1;
               else
               *cat = idx*NCATS + s->curoffset;
             */
            if (idx < 0)
                *cat = -((-idx) << SHIFT) + s->curoffset + 1;
            else
                *cat = (idx << SHIFT) + s->curoffset;
 
            return 1;
        }
    }
}
 
/*!
 * \brief Get number of null values.
 *
 * Get a number of null values from stats structure.
 *
 * Note: when reporting values which appear in a map using
 * Rast_next_cell_stats(), to get stats for null, call
 * Rast_get_stats_for_null_value() first, since Rast_next_cell_stats() does
 * not report stats for null.
 *
 * \param count count
 * \param s pointer to Cell_stats structure which holds cell stats info
 */
void Rast_get_stats_for_null_value(long *count, const struct Cell_stats *s)
{
    *count = s->null_data_count;
}
 
/*!
 * \brief Free cell stats structure
 *
 * The memory associated with structure <i>s</i> is freed. This
 * routine may be called any time after calling Rast_init_cell_stats().
 *
 * \param s pointer to Cell_stats structure
 */
void Rast_free_cell_stats(struct Cell_stats *s)
{
    int i;
 
    for (i = 1; i <= s->N; i++)
        G_free(s->node[i].count);
    G_free(s->node);
}