Benchmarks

regex benchmarks

The generated measurement tables for the regex module — every case, the harness that measured it, and how to reproduce it.

The generated benchmark tables for the regex module — a from-scratch lazy DFA with linear-time search — against std::regex, Boost.Regex and Google RE2. How the race is set up (the standalone stdlib/regex/bench/ project, output verification across every engine that can finish the case before anything is timed, the rxdiff differential suite) is on the module page; this page holds the numbers, their stamps, and the commands that reproduce them.

Representative medians below; the full table follows and carries its own tally. Pinned P-core, medians over interleaved repetitions. Boost's single win is compiling a 64-byte pure literal: analysis Boost skips and match time repays.

Two 16 MB literal scans — run_padded_literal_16M and sweep_16M — score as parity with RE2 in the table below. They are memcmp-bound rather than automaton-bound, so the comparison is between two prefilters doing almost identical work, and the margin is thin enough that RXBENCH_ASSERT=1 can go red on them; the response is to read the margin, not to widen the threshold.

Representative cases

Measured by stdlib/regex/bench/rxbench.cpp; reproduce with RXBENCH_REP_TABLE=docs/bench/regex-representative.md RXBENCH_ROWS='pat_literal_present=status=200 on a 4 MB log;pat_digits=[0-9]+ (search);pat_anchor_end=1274$ (end-anchored, 4 MB);findall_digits=find-all [0-9]+ (256 KB);hugescan=64 MB absent-pattern scan;compile_class_email=compile [a-z]+[a-z.]+;redos2_alt2_N28=**ReDoS** (a|aa)+$, N=28;xl_redos_altstar_16M=**ReDoS at 16 MB** (a|a)*c' ./build/regexbench/rxbench --benchmark_repetitions=7 --benchmark_enable_random_interleaving=true.

case	cheatah	std::regex	Boost	RE2	vs RE2
`status=200` on a 4 MB log	26.5 ns	649.9 ns	95.0 ns	46.6 ns	1.8×
`[0-9]+` (search)	6.8 ns	74.1 ns	44.5 ns	28.7 ns	4.3×
`1274$` (end-anchored, 4 MB)	6.0 ns	35.713 ms	107.9 ns	30.0 ns	5.0×
find-all `[0-9]+` (256 KB)	428.83 us	3.512 ms	3.304 ms	1.748 ms	4.1×
64 MB absent-pattern scan	3.391 ms	526.047 ms	35.253 ms	5.144 ms	1.5×
compile `[a-z]+@[a-z.]+`	218.8 ns	22.30 us	1.02 us	1.96 us	9.0×

| ReDoS (a|aa)+$, N=28 | 3.4 ns | — | — | 28.1 ns | 8.2× | | ReDoS at 16 MB (a|a)*c | 3.927 ms | — | — | 19.393 ms | 4.9× |

The complete comparison — every benchmarked case, all four engines

Measured by stdlib/regex/bench/rxbench.cpp; reproduce with RXBENCH_ASSERT=1 RXBENCH_TABLE=docs/bench/regex-vs-engines.md ./build/regexbench/rxbench --benchmark_repetitions=7 --benchmark_enable_random_interleaving=true --benchmark_report_aggregates_only=true.

case	cheatah	std::regex	boost	RE2	vs std	vs boost	vs RE2
compile_alternation	448.5 ns	645.2 ns	772.3 ns	2.46 us	1.44x ✅	1.72x ✅	5.48x ✅
compile_class_email	218.8 ns	22.30 us	1.02 us	1.96 us	101.96x ✅	4.65x ✅	8.97x ✅
compile_ip	308.7 ns	47.35 us	1.47 us	2.88 us	153.39x ✅	4.77x ✅	9.34x ✅
compile_literal	288.6 ns	438.4 ns	330.0 ns	1.74 us	1.52x ✅	1.14x ⚪	6.02x ✅
compile_repetition	289.9 ns	23.54 us	1.56 us	3.42 us	81.20x ✅	5.37x ✅	11.79x ✅
compilescale_alt50	9.18 us	17.77 us	12.15 us	11.45 us	1.94x ✅	1.32x ✅	1.25x ✅
compilescale_literal64	1.40 us	2.61 us	598.1 ns	6.50 us	1.87x ✅	0.43x ❌	4.65x ✅
compilescale_nest100	3.26 us	8.41 us	4.18 us	20.59 us	2.58x ✅	1.28x ✅	6.32x ✅
find_anchor_end	12.2 ns	35.799 ms	109.6 ns	33.3 ns	2944495.28x ✅	9.02x ✅	2.74x ✅
find_digits	12.9 ns	74.3 ns	49.5 ns	65.8 ns	5.74x ✅	3.82x ✅	5.09x ✅
find_email	108.9 ns	997.0 ns	140.4 ns	132.9 ns	9.16x ✅	1.29x ✅	1.22x ✅
find_ip_absent	4.457 ms	58.101 ms	9.978 ms	4.601 ms	13.04x ✅	2.24x ✅	1.03x ⚪
findall_alternation	193.18 us	3.826 ms	212.66 us	462.62 us	19.81x ✅	1.10x ⚪	2.39x ✅
findall_digits	428.83 us	3.512 ms	3.304 ms	1.748 ms	8.19x ✅	7.71x ✅	4.08x ✅
findall_key_value	172.80 us	2.613 ms	269.43 us	332.84 us	15.12x ✅	1.56x ✅	1.93x ✅
findall_word	433.75 us	3.569 ms	2.799 ms	1.721 ms	8.23x ✅	6.45x ✅	3.97x ✅
findlate_xmarker_4M	56.19 us	31.797 ms	1.198 ms	56.72 us	565.85x ✅	21.31x ✅	1.01x ⚪
full_digits_yes	6.1 ns	79.2 ns	66.1 ns	21.1 ns	12.97x ✅	10.82x ✅	3.46x ✅
full_email_no	5.5 ns	69.8 ns	52.2 ns	20.1 ns	12.73x ✅	9.53x ✅	3.66x ✅
full_email_yes	15.2 ns	231.3 ns	118.7 ns	32.0 ns	15.25x ✅	7.82x ✅	2.11x ✅
hugescan	3.391 ms	526.047 ms	35.253 ms	5.144 ms	155.15x ✅	10.40x ✅	1.52x ✅
pat_alt_absent	2.398 ms	61.334 ms	2.255 ms	4.554 ms	25.57x ✅	0.94x ⚪	1.90x ✅
pat_alternation	17.9 ns	377.2 ns	52.7 ns	45.2 ns	21.10x ✅	2.95x ✅	2.53x ✅
pat_anchor_end	6.0 ns	35.713 ms	107.9 ns	30.0 ns	5957941.81x ✅	18.01x ✅	5.00x ✅
pat_anchor_start	6.5 ns	60.6 ns	45.9 ns	29.4 ns	9.26x ✅	7.01x ✅	4.49x ✅
pat_class_quant	16.0 ns	231.9 ns	52.1 ns	42.3 ns	14.53x ✅	3.26x ✅	2.65x ✅
pat_digits	6.8 ns	74.1 ns	44.5 ns	28.7 ns	10.96x ✅	6.58x ✅	4.25x ✅
pat_dotstar	94.2 ns	1.40 us	100.9 ns	105.9 ns	14.87x ✅	1.07x ⚪	1.12x ⚪
pat_email_absent	5.019 ms	79.415 ms	31.412 ms	4.545 ms	15.82x ✅	6.26x ✅	0.91x ⚪
pat_email	59.8 ns	987.7 ns	321.3 ns	89.0 ns	16.52x ✅	5.38x ✅	1.49x ✅
pat_escapes	29.4 ns	254.4 ns	174.6 ns	33.3 ns	8.64x ✅	5.93x ✅	1.13x ⚪
pat_ip_absent	4.344 ms	58.363 ms	22.530 ms	4.602 ms	13.43x ✅	5.19x ✅	1.06x ⚪
pat_key_value	20.0 ns	657.8 ns	77.2 ns	37.0 ns	32.87x ✅	3.86x ✅	1.85x ✅
pat_literal_absent	660.41 us	36.971 ms	4.085 ms	926.98 us	55.98x ✅	6.19x ✅	1.40x ✅
pat_literal_present	26.5 ns	649.9 ns	95.0 ns	46.6 ns	24.56x ✅	3.59x ✅	1.76x ✅
pat_nested_groups	27.4 ns	683.8 ns	106.3 ns	74.2 ns	24.96x ✅	3.88x ✅	2.71x ✅
pat_prefix_class	13.5 ns	388.7 ns	59.0 ns	31.0 ns	28.79x ✅	4.37x ✅	2.30x ✅
pat_repetition	37.7 ns	1.83 us	775.1 ns	73.6 ns	48.56x ✅	20.55x ✅	1.95x ✅
pat_word	16.6 ns	246.0 ns	298.9 ns	42.9 ns	14.80x ✅	17.98x ✅	2.58x ✅
real_find_hex	31.1 ns	661.8 ns	111.2 ns	76.5 ns	21.30x ✅	3.58x ✅	2.46x ✅
real_findall_ts	306.47 us	3.153 ms	618.55 us	411.05 us	10.29x ✅	2.02x ✅	1.34x ✅
real_hex_absent	92.24 us	33.788 ms	3.148 ms	672.72 us	366.30x ✅	34.12x ✅	7.29x ✅
real_hex	18.9 ns	666.9 ns	103.6 ns	37.3 ns	35.31x ✅	5.48x ✅	1.97x ✅
real_keylist	212.2 ns	4.03 us	3.44 us	204.9 ns	18.98x ✅	16.23x ✅	0.97x ⚪
real_quoted	23.8 ns	145.5 ns	59.5 ns	36.2 ns	6.12x ✅	2.50x ✅	1.52x ✅
real_timestamp	38.9 ns	589.7 ns	240.0 ns	85.5 ns	15.15x ✅	6.16x ✅	2.20x ✅
real_uuid	151.3 ns	1.75 us	638.3 ns	151.6 ns	11.58x ✅	4.22x ✅	1.00x ⚪
redos2_alt2_N16	3.4 ns	—	—	27.9 ns	—	—	8.22x ✅
redos2_alt2_N28	3.4 ns	—	—	28.1 ns	—	—	8.19x ✅
redos2_dotstar3_4M	1.542 ms	—	—	4.551 ms	—	—	2.95x ✅
redos_altstar_N16	7.8 ns	—	—	35.4 ns	—	—	4.54x ✅
redos_altstar_N20	8.7 ns	—	—	41.2 ns	—	—	4.71x ✅
redos_altstar_N24	9.5 ns	—	—	45.7 ns	—	—	4.83x ✅
redos_altstar_N28	10.5 ns	—	—	50.3 ns	—	—	4.78x ✅
redos_nested_N16	3.4 ns	—	—	27.8 ns	—	—	8.11x ✅
redos_nested_N20	3.4 ns	—	—	28.0 ns	—	—	8.20x ✅
redos_nested_N24	3.4 ns	—	—	28.0 ns	—	—	8.22x ✅
redos_nested_N28	3.4 ns	—	—	28.0 ns	—	—	8.32x ✅
run_class_absent_16M	647.76 us	—	—	19.510 ms	—	—	30.12x ✅
run_class_present_16M	633.67 us	—	—	19.298 ms	—	—	30.45x ✅
run_padded_literal_16M	281.32 us	125.707 ms	4.846 ms	281.31 us	446.85x ✅	17.23x ✅	1.00x ⚪
run_spaces_16M	7.762 ms	133.966 ms	198.959 ms	19.435 ms	17.26x ✅	25.63x ✅	2.50x ✅
run_tailclass_16M	3.873 ms	—	—	19.305 ms	—	—	4.98x ✅
shape_absent	56.53 us	32.284 ms	1.258 ms	56.86 us	571.05x ✅	22.25x ✅	1.01x ⚪
shape_end	56.52 us	32.772 ms	1.213 ms	56.54 us	579.85x ✅	21.47x ✅	1.00x ⚪
shape_everywhere	19.8 ns	468.1 ns	77.9 ns	36.9 ns	23.64x ✅	3.93x ✅	1.86x ✅
shape_start	16.6 ns	83.2 ns	51.5 ns	32.5 ns	5.01x ✅	3.10x ✅	1.95x ✅
sweep_16K	116.6 ns	130.88 us	5.16 us	136.5 ns	1122.14x ✅	44.27x ✅	1.17x ✅
sweep_16M	300.90 us	133.809 ms	5.212 ms	301.48 us	444.69x ✅	17.32x ✅	1.00x ⚪
sweep_1K	13.7 ns	8.27 us	357.0 ns	32.6 ns	605.26x ✅	26.13x ✅	2.38x ✅
sweep_1M	10.35 us	8.369 ms	317.06 us	10.42 us	808.69x ✅	30.64x ✅	1.01x ⚪
sweep_256K	2.32 us	2.125 ms	79.58 us	2.32 us	916.55x ✅	34.32x ✅	1.00x ⚪
tiny_digit_hit	6.7 ns	57.1 ns	44.4 ns	28.8 ns	8.48x ✅	6.60x ✅	4.27x ✅
tiny_digit_miss	6.3 ns	53.8 ns	51.8 ns	27.8 ns	8.58x ✅	8.25x ✅	4.43x ✅
tiny_email_hit	9.1 ns	66.3 ns	54.5 ns	28.7 ns	7.27x ✅	5.98x ✅	3.15x ✅
tiny_email_miss	13.2 ns	81.2 ns	62.2 ns	28.4 ns	6.16x ✅	4.72x ✅	2.15x ✅
tiny_full_tok16	14.7 ns	189.6 ns	84.6 ns	32.3 ns	12.92x ✅	5.76x ✅	2.20x ✅
xl_email_absent_16M	20.989 ms	—	—	19.460 ms	—	—	0.93x ⚪
xl_find_budget_16M	661.76 us	187.178 ms	224.054 ms	23.313 ms	282.85x ✅	338.57x ✅	35.23x ✅
xl_literal_storm_16M	2.846 ms	—	—	3.959 ms	—	—	1.39x ✅
xl_redos_altstar_16M	3.927 ms	—	—	19.393 ms	—	—	4.94x ✅
xl_redos_nested_16M	3.5 ns	—	—	27.8 ns	—	—	8.02x ✅
xl_reverse_alive_16M	651.06 us	—	—	19.429 ms	—	—	29.84x ✅

Tally — vs std: 64 faster / 0 parity / 0 slower; vs boost: 59 faster / 4 parity / 1 slower; vs re2: 68 faster / 15 parity / 0 slower.

cheatah ties or beats RE2 on every case.

Honest reading

RE2 is timed in its out-of-box configuration (UTF-8, leftmost-first) — the configuration real RE2 users get; offsets are cross-checked against RE2's longest-match + Latin-1 mode, which matches cheatah's documented leftmost-longest byte semantics. Rows where both engines sit at memory bandwidth (large absent scans that reduce to memchr) cannot separate meaningfully and score as parity — that is physics, not engine quality. On the pathological inputs, std::regex runs exponentially (seconds at N=28; unrunnable at 16 MB — those rows exclude it) and Boost aborts with a "complexity exceeded" exception; cheatah and RE2 both stay linear, and cheatah answers faster. Because it is a DFA, no input can ever make cheatah backtrack.

Reproduce

cmake -S stdlib/regex/bench -B build/regexbench -DCMAKE_BUILD_TYPE=Release
cmake --build build/regexbench -j
./build/regexbench/rxdiff                       # differential tests vs RE2-as-oracle
taskset -c 4 env RXBENCH_ASSERT=1 RXBENCH_TABLE=/tmp/rxtable.md \
    ./build/regexbench/rxbench --benchmark_repetitions=7 \
    --benchmark_enable_random_interleaving=true \
    --benchmark_report_aggregates_only=true     # exit 0 = no case slower than RE2

(taskset pins to one performance core on hybrid CPUs; RXBENCH_ASSERT=1 makes the run fail if cheatah is slower than RE2 anywhere; RXBENCH_TABLE writes the full Markdown table.)

--benchmark_enable_random_interleaving matters more here than the repetition count. All four engines are registered per case, so without it cheatah's seven repetitions run as one block, then std::regex's, then Boost's, then RE2's — and any clock or thermal drift over that window lands on whichever engine ran last rather than cancelling out of the ratio. Interleaved, the repetitions of all four are scattered through the run, which is what makes a per-case rival / cheatah figure a property of the engines rather than of the ordering.

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