Pointer question about Discrete2d

[Paul E Johnson]

There is a pointer usage in swarm, src/space/Discrete2d.m, that I don't
understand.

Discrete2d.h declares
long * offsets;

It is allocated in Discrete2d.m

- makeOffsets
{
  unsigned i;
  // precalculate offsets based on the y coordinate. This lets
  // us avoid arbitrary multiplication in array lookup.
  offsets = [getZone (self) alloc: ysize * sizeof (*offsets)];
  for (i = 0; i < ysize; i++)
    offsets[i] = xsize * i; // cache this multipliction
  return self;
}

I don't understand why the aloc is not 
offsets = [getZone (self) alloc: ysize * sizeof (long)];

I don't get what sizeof(*offsets) means.

Can someone explain for a poor, old country doctor?
-- 
Paul E. Johnson                       email: address@hidden
Dept. of Political Science            http://lark.cc.ukans.edu/~pauljohn
University of Kansas                  Office: (785) 864-9086
Lawrence, Kansas 66045                FAX: (785) 864-5700

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