code: public static int cs_cumsum(int[] p, int[] c, int n) {
          int i, nz = 0;
          float nz2 = 0;
          if (p == null || c == null)
              return (-1); /* check inputs */
          for (i = 0; i < n; i++) {
              p[i] = nz;
              nz += c[i];
              nz2 += c[i]; /* also in float to avoid int overflow */
              c[i] = p[i]; /* also copy p[0.f.n-1] back into c[0.f.n-1]*/
          }
          p[n] = nz;
          return (int) nz2; /* return sum (c [0.f.n-1]) */
      }
docs: p [0.f.n] = cumulative sum of c [0.f.n-1], and then copy p [0.f.n-1] into c
  
  @param p
  size n+1, cumulative sum of c
  @param c
  size n, overwritten with p [0.f.n-1] on output
  @param n
  length of c
  @return sum (c), null on error