Silently remove duplicate consecutive prism vertices

[oskooi]

Fixes NanoComp/meep#1905.

[stevengj]

Note that a CHECK failure will call exit, which won't be that nice from e.g. Python.

[stevengj]

For example, to delete consecutive equal vertices, including the last point, you could do:

int i = 0; // last non-deleted vertex
for (j = 1; j < num_vertices; ++j) {
    if (!vector3_equal(vertices[i], vertices[j])) {
        i += 1;
        if (i < j) vertices[i] = vertices[j];
    }
}
num_vertices = i + 1 - vector3_equal(vertices[0], vertices[i]);
prsm->vertices.num_items = num_vertices;

[stevengj]

(In principle, you could then call realloc to save a bit of memory in vertices, but it's probably not worth it — realloc is potentially unsafe if the memory was not allocated with malloc.)

[oskooi]

Fixed. I included a realloc if the number of vertices has changed since the vertices array (via the items member of prsm->vertices) is allocated with malloc:

libctl/utils/ctl-io.scm

Lines 246 to 248 in 76deb2a

	(print c-var-name-str ".items = "
	(malloc (c-type-string type-name) c-var-name-str ".num_items")
	";\n")