35 lines
1.1 KiB
Markdown
35 lines
1.1 KiB
Markdown
# Description
|
|
|
|
🌐 **English** · [Dansk](Description-da) · [Bahasa Melayu](Description-ms)
|
|
|
|
## Purpose
|
|
|
|
The program shows how fast a CPU is. How fast it looks depends on how the
|
|
program is written, so the number is a measure of the CPU and the code
|
|
together, not of the CPU alone.
|
|
|
|
## What it does
|
|
|
|
It tests every number from 0 to 1,000,000 with `is_prime_avx2`, which uses
|
|
AVX2 trial division by 6k ± 1 (four divisors per step). It prints each prime
|
|
on its own line and writes a summary line to standard error:
|
|
|
|
```text
|
|
Found 78498 primes from 0 to 1000000 in 13.806 ms
|
|
```
|
|
|
|
78,498 is the known count of primes up to 1,000,000, so the summary line also
|
|
works as a correctness check.
|
|
|
|
## Why the time depends on the code
|
|
|
|
The same CPU gives very different times for different programs:
|
|
|
|
- the algorithm (trial division, a sieve, a segmented sieve),
|
|
- the instruction set used (scalar code, AVX2, AVX-512),
|
|
- compiler and flags (`-O3 -mavx2`, MSVC `/O2 /arch:AVX2`),
|
|
- what is measured (only the search, or also printing to a console).
|
|
|
|
Here only the search is timed. Output is collected first and printed
|
|
afterwards, so console speed does not change the number.
|