Each new program under examples/ isolates one distinct feature rather
than being a general purpose tool like the existing rxgrep.c:
binary_scan.c (raw byte-range classes including an embedded NUL and
an embedded 0x0A), utf8_scripts.c (\w across Latin/Greek/Cyrillic/CJK
text, code point versus byte offsets), ascii_logparse.c (named groups
against structured log text), redos_atomic.c (atomic groups and
possessive quantifiers timed directly against the unprotected form of
the textbook (a+)+b ReDoS shape), empty_match_rule.c (CPython's
undocumented empty-match retry rule, verified: \d*? against
"123abc456" gives 16 matches, not 9), and large_file_search.c
(Input_from_file's mmap-backed reading on a generated 100MB file,
with elapsed time and peak RSS printed). Every example was compiled
and run while writing it; the claims in each file's top comment are
checked against its own output, not written by hand and left
unverified.
Also adds examples/bench_vs_posix.c, a direct, honestly reported
comparison against the C standard library's own <regex.h>
(regcomp/regexec) on six scenarios at multi-megabyte or
multi-hundred-thousand-line scale, using only pattern syntax valid
for both engines so they run the identical pattern text. glibc's
DFA-backed engine wins five of six scenarios by 2x-35x, which is the
expected outcome of a roughly 2000-line backtracking interpreter
built for Python `re` compatibility competing against a mature,
heavily optimized engine with a much smaller feature set; the sixth
scenario has no POSIX equivalent at all (an atomic group). Every
scenario's match count is cross-checked between the two engines as an
independent correctness signal beyond the existing CPython-derived
test suite.
Two real issues were found and fixed while building this benchmark,
not left in: iterating regexec() over an advancing string pointer is
quadratic in practice (no way to bound the search without an implicit
NUL-scan on every call), fixed by using REG_STARTEND instead; and a
signed integer overflow (undefined behavior, caught by UBSan) in the
benchmark's own pseudo-random text generator, fixed by using an
unsigned accumulator.
README.md and USAGE.md gain pointers to examples/README.md (the new
per-example index) and a "Benchmarks" section summarizing the
POSIX comparison honestly, including where it loses. The Makefile
gains a `make examples` target building all seven programs.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EjuMk8kY9SDus1wWe2K9xY
