If you look at the map file that is generated from the code generation tools, it should indicate that floating point libraries are included when your arguments are float. Including these libraries would increase the code size in the .text section.
Regarding the issue you first observed, you are running into numerical overflow as you accumulate the 300 samples into a variable. When you the type int, this is referring to a signed int (16-bit value with range from -32768 to 32767). The data types of the MSP430 are described in the MSP430 Optimizing C/C++ Compiler User's Guide in Section 5.5.