SSE4 added FRNDINT (x87) and ROUNDSS/SD (xmm) to do this task purely on hardware.

Further, if one is seriously determined, there are ways to perform bitwise on floating-point registers directly. On XMM, it's trivial: just take advantage of the integer (and non-integer, e.g. XORAPS) instruction available.

On x87, one can take advantage of the direct mapping between MMX and x87 registers to manipulate them using MMX's integer instructions. This has problems, but as I said -- seriously determined.