1.1 KiB
1.1 KiB
Description
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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:
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.