What's the main reason ripgrep is fast?

According to the repository, ripgrep's speed comes from multiple factors outlined in [README.md:L183-L210]:

1. Rust's regex engine - It uses finite automata, SIMD, and aggressive literal optimizations to make searching very fast. PCRE2 support is also available via the -P/--pcre2 flag.

2. Unicode support with performance - Rust's regex library maintains performance while supporting full Unicode by building UTF-8 decoding directly into its deterministic finite automaton engine.

3. Smart search strategy selection - It supports searching with either memory maps (better for single files) or incremental buffering (better for large directories), and automatically chooses the best strategy for you.

4. Efficient ignore pattern matching - It applies .gitignore patterns using a RegexSet, allowing a single file path to be matched against multiple glob patterns simultaneously.

5. Parallel directory iteration - It uses a lock-free parallel recursive directory iterator via crossbeam and ignore libraries.

In essence, ripgrep combines highly optimized regex matching algorithms with smart architectural decisions about how to search files and directories efficiently.

FOLLOW_UPS:

• How does ripgrep handle Unicode text compared to grep?
• What file types does ripgrep automatically skip by default?
• Can ripgrep use PCRE2 instead of its default regex engine?