Generate 3 uniform random variables that sum to 0

gistfile1.txt

See the question in http://stackoverflow.com/questions/13008383/generate-3-uniform-random-variables-that-sum-to-0

The following pseudo code output a, b, and c. Function rand() returns real number uniformly distributed in (0,1).

s = rand() * 3;
r = rand();
if (s < 1) {
  a = r;
  b = 1 - 2*r;
  c = r - 1;
} else if (s < 2) {
  a = 1 - 2*r;
  b = r - 1;
  c = r;
} else {
  a = r - 1;
  b = r;
  c = 1 - 2*r;
}