C
Summary - Performance
Combine profiling, cache and loop optimization to write a copy function.
Summary - Performance
In this group you learned profiling, cache effects, loop optimization, inline and memory alignment. Now you'll combine them into an aligned and unrolled copy function.
The copy_block function copies an int array with 4-way unroll; each iteration copies 4 elements. It copies the {1,2,3,4} array to a destination and prints the destination. All output is deterministic: kopya 1 2 3 4.
Exercise copy_block function
Write void copy_block(const int *src, int *dst, int n): int i;, 4-way unroll for (i = 0; i + 3 < n; i += 4) { dst[i] = src[i]; dst[i+1] = src[i+1]; dst[i+2] = src[i+2]; dst[i+3] = src[i+3]; }, remainder for (; i < n; i++) dst[i] = src[i];. In main declare int src[] = {1,2,3,4};, int dst[4] = {0};, call copy_block(src, dst, 4); and print printf("kopya: %d %d %d %d\n", dst[0], dst[1], dst[2], dst[3]);.
Show example solution
#include <stdio.h>
void copy_block(const int *src, int *dst, int n) {
int i;
for (i = 0; i + 3 < n; i += 4) {
dst[i] = src[i];
dst[i+1] = src[i+1];
dst[i+2] = src[i+2];
dst[i+3] = src[i+3];
}
for (; i < n; i++) dst[i] = src[i];
}
int main(void) {
int src[] = {1,2,3,4};
int dst[4] = {0};
copy_block(src, dst, 4);
printf("kopya: %d %d %d %d\n", dst[0], dst[1], dst[2], dst[3]);
return 0;
}
Next steps
You learned the performance basics: profiling, cache, loop unrolling, inline and alignment. These are core tools of systems programming.
Next steps: CPU counters with perf stat, 8- or 16-element parallel processing with SIMD vector instructions, branch prediction with __builtin_expect, and multi-node memory management with numa. The patterns you learned are the foundation of these advanced techniques.
Test yourself
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How does copy_block get faster?
- Column-major
- 4-way unroll
- Slow loop
- Random access
Show answer
4-way unroll — 4-way unroll copies 4 elements per iteration; overhead drops.
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Match performance tools
- clock
- Measures time
- row-major
- Cache friendly
- unroll
- Cuts loop overhead
- _Alignof
- Gives alignment
Next lesson: Project design
