Build into dist/, list primes to 1,000,000 with timing, add wiki

docs/wiki/Build-and-Run.md

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+# Build and run
+
+**English**
+
+The `Makefile` is in the repository root and puts the executable in `dist/`.
+It needs `gcc` (Linux, or MinGW-w64 / MSYS2 on Windows) and a CPU with AVX2.
+
+```bash
+make
+```
+
+```bash
+make run
+```
+
+```bash
+make clean
+```
+
+To save the primes and still see the time, redirect only standard output:
+
+```bash
+./dist/prime_avx2 > primes.txt
+```

docs/wiki/Description.md

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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.

docs/wiki/Home.md

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+# prime-numbers-c
+
+**English**
+
+A small C program that lists every prime number from 0 to 1,000,000 and
+reports how long it took.
+
+- [Description](Description): what the program is for
+- [Results](Results): measured times on real hardware
+- [Build and run](Build-and-Run): `make`, `make run`

docs/wiki/Results.md

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+# Results
+
+**English**
+
+Time to find all primes from 0 to 1,000,000. Only the search is timed.
+
+| CPU | Result |
+| --- | --- |
+| 13th Gen Intel(R) Core(TM) i5-13600K | Found 78498 primes from 0 to 1000000 in 20.977 ms |
+
+A result is only comparable with another when the code, compiler and flags
+are the same. To add a result, run the program on your machine (see
+[Build and run](Build-and-Run)) and add a row with your CPU name and the
+summary line.

docs/wiki/_Sidebar.md

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+- [Home](Home)
+- [Description](Description)
+- [Results](Results)
+- [Build and run](Build-and-Run)