I agree with explicit parentheses but please be careful about assuming associativity! The risk when handling floating-point arithmetic in particular is that associativity breaks, and suddenly a + (b + c) does NOT equal (a + b) + c. Not only can these lead to unexpected and hard-to-trace failure patterns, but depending on the details, they also can introduce memory overflow/underflow vulnerabilities.
If you're going for bit-for-bit equivalence of float values, then even with a single operation you're relying on compiler flags, architecture, the phase of the moon... I'm hard-pressed to think of any memory safety issues though.