register as input in C

i found it while i was going through some solutions

inline void fastread(int *a) {

register char c;

while(c<33) c=getchar_unlocked();

*a=0;

while(c>=33) {

a=a*10+c-'0'; c=getchar_unlocked();

} }

can any one pls explain what are we trying to achieve with this how can it reduse the run time effectively !!