As the function documentation states, the expected value must be read
again after a call to atomic_cas_ptr. This is due to the fact that if the
values are not the same, the __atomic builtin version will store the
current value into the expected value.
The new value given to the atomic_cas_ptr function was the address of the
new value, not the new value itself. The behavior of the atomic_cas_ptr is
what caused the test to pass on systeems that implement the __atomic
builtins. On older systems that do not implement it, the expected value
was never modified which caused the test to hang.
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