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+# Description
+
+**English**
+
+## 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.