source: tags/ms_r18q1/TREEGEN/spreadin.c

#define  __MODUL__
#include "spreadin.h"
#include <stdlib.h>

Spreading newSpreading(double *value, int values) {
    Spreading s;
    int       v;
    double    val = 0.0,
              sum = 0.0;

    s = malloc(sizeof(struct S_Spreading));
    if (!s) outOfMemory();

    assert(values>0);

    s->values = values;
    s->border = malloc(sizeof(*(s->border))*values);
    if (!s->border) outOfMemory();

    for (v = 0; v<values; v++) sum += value[v];      // Summe bilden

    for (v = 0; v<values; v++) {
        val          += value[v];
        s->border[v]  = (val/sum)*RAND_MAX;
    }

    s->border[values-1] = RAND_MAX;

    return s;
}
void freeSpreading(Spreading s) {
    free(s->border);
    free(s);
}
int spreadRand(Spreading s) {
    int val = rand(),
        l   = 0,
        h   = s->values-1,
        m;

    while (1) {
        m = (l+h)/2;

        if (val<=s->border[m]) {
            if (m==0 || val>s->border[m-1]) break;
            h = m;
        }
        else {
            if (m==(h-1)) {
                if (val<=s->border[h]) {
                    m = h;
                    break;
                }
            }

            l = m;
        }
    }

    assert(m>=0 && m<s->values);
    assert(val<=s->border[m]);
    assert(m==0 || val>=s->border[m-1]);

    return m;
}