What is TH_API, and where is THFloatTensor_data?

What is the meaning of TH_API ? Where does it defined ?
And, in the following code, how to explain the THTensor_(storage) part ?

/**** access methods ****/
TH_API THStorage* THTensor_(storage)(const THTensor *self);

By the way, where is THFloatTensor_data and THCudaIntTensor_data something like that ?