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