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This is my attempt to convert the blazingly fast assembler routine for calculating parity into a C function. The original comes from here: https://www.microchip.com/forums/m4762.aspx Unfortunately Microchip have killed off the board where the original discussion took place at http://asp.microchip.com/webboard/wbpx.dll/~DevTools/read?21443,5 #include <xc.h> //returns 0x00 (even parity) or 0x80 (odd parity) unsigned char parity(volatile unsigned char dat) //("volatile" is required because no C code reads the parameter) { asm("swapf parity@dat,w"); //assume correct bank is still selected asm("xorwf parity@dat,w"); //W has 8 bits reduced to 4 with same parity asm("addlw 41h"); // bit 1 becomes B0^B1 and bit 7 becomes B6^B7 asm("iorlw 7Ch"); // for carry propagation from bit 1 to bit 7 asm("addlw 2"); // Done! the parity bit is bit 7 of W asm("andlw 80h"); // set NZ if odd parity, and leave 00 or 80 in W asm("return"); return 1; //dummy instruction to defeat "no return value" error } void main(void) { unsigned char idx=0; while(1) { PORTA = parity(idx); idx++; } } I'm not sure if there's a cleaner way to suppress the "no return value" error, without generating extra code.