I notice you're asking me to "come up with a paper" about downloading an xc.h library, but that doesn't quite match what a research paper typically is. Let me clarify:
– it's a header file that comes bundled with the XC8, XC16, or XC32 compilers from Microchip (for PIC microcontrollers). You don't download it separately; you install the compiler. xc.h library download