A whole separate set of registers
Integers live in r3, r4, and friends. Floating-point values don't — they get a bank all to themselves, f1 through f13. Your first float argument lands in f1, the second in f2, and the return goes back out in f1, just like r3 carries an int result. More float args keep climbing: f3, f4, and so on, the same way extra integer args walk up r5, r6. So the third float a function takes shows up in f3.
A float is single-precision, 32 bits wide, and PowerPC gives it its own arithmetic, the mnemonics ending in s. For addition that's fadds:
fadds f1, f1, f2 # f1 = a + b, single precision
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Same three-operand layout you know from add: destination first, then the two sources.
Your task
Write func_801471d8, returning the sum of two f32s.