Time taken for memcpy decreases after certain point
- by tss
I ve a code which increases the size of the memory(identified by a pointer) exponentially.
Instead of realloc, I use malloc followed by memcpy..
Something like this..
int size=5,newsize;
int *c = malloc(size*sizeof(int));
int *temp;
while(1)
{
newsize=2*size;
//begin time
temp=malloc(newsize*sizeof(int));
memcpy(temp,c,size*sizeof(int));
//end time
//print time in mili seconds
c=temp;
size=newsize;
}
Thus the number of bytes getting copied is increasing exponentially.
The time required for this task also increases almost linearly with the increase in size. However after certain point, the time taken abruptly reduces to a very small value and then remains constant.
I recorded time for similar code, copyin data(Of my own type)
5 -> 10 - 2 ms
10 -> 20 - 2 ms
.
.
2560 -> 5120 - 5 ms
.
.
20480 -> 40960 - 30 ms
40960 -> 91920 - 58 ms
367680 -> 735360 - 2 ms
735360 -> 1470720 - 2 ms
1470720 -> 2941440 - 2 ms
What is the reason for this drop in time ? Does a more optimal memcpy method get called when the size is large ?
