Short-circuit empty key lookup paths

[dduan]

Skip unsafe-buffer setup in key lookup helpers when the index list is empty.

Also decode key substrings directly from pointer ranges in makeString to avoid repeated slice construction on the hot key path.

[github-actions]

Comparing results between 'main' and 'pull_request'

Host 'runnervmkj6or' with 4 'x86_64' processors with 15 GB memory, running:
#18~24.04.1-Ubuntu SMP Sat Jun 28 04:46:03 UTC 2025

TOMLDecoderBenchmarks

Decode toml.io example metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (μs) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	64	65	65	66	70	85	381	7302
pull_request	66	66	67	68	72	98	165	7202
Δ	2	1	2	2	2	13	-216	-100
Improvement %	-3	-2	-3	-3	-3	-15	57	-100

Retains: results within specified thresholds, fold down for details.

Retains *	p0	p25	p50	p75	p90	p99	p100	Samples
main	605	605	605	605	605	605	605	7302
pull_request	604	604	604	605	605	605	605	7202
Δ	-1	-1	-1	0	0	0	0	-100
Improvement %	0	0	0	0	0	0	0	-100

Parse toml.io example metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (ns) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	5530	5651	5691	5731	5803	12095	31158	10000
pull_request	5590	5743	5791	5851	6135	15807	139180	10000
Δ	60	92	100	120	332	3712	108022	0
Improvement %	-1	-2	-2	-2	-6	-31	-347	0

Retains: results within specified thresholds, fold down for details.

Retains *	p0	p25	p50	p75	p90	p99	p100	Samples
main	13	14	14	14	14	14	14	10000
pull_request	13	14	14	14	14	14	14	10000
Δ	0	0	0	0	0	0	0	0
Improvement %	0	0	0	0	0	0	0	0

decode canada.toml metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (ms) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	266	266	267	267	268	268	268	4
pull_request	265	265	266	266	267	267	267	4
Δ	-1	-1	-1	-1	-1	-1	-1	0
Improvement %	0	0	0	0	0	0	0	0

Retains: results within specified thresholds, fold down for details.

Retains (K) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	1674	1674	1674	1674	1674	1674	1674	4
pull_request	1674	1674	1674	1674	1674	1674	1674	4
Δ	0	0	0	0	0	0	0	0
Improvement %	0	0	0	0	0	0	0	0

decode twitter.toml metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (μs) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	8908	8954	8978	9028	9085	9273	9469	111
pull_request	8906	8954	8978	9019	9052	9249	9526	111
Δ	-2	0	0	-9	-33	-24	57	0
Improvement %	0	0	0	0	0	0	-1	0

Retains: results within specified thresholds, fold down for details.

Retains (K) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	68	68	68	68	68	68	68	111
pull_request	68	68	68	68	68	68	68	111
Δ	0	0	0	0	0	0	0	0
Improvement %	0	0	0	0	0	0	0	0

parse GitHub events archive metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (ms) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	156	157	158	160	169	169	169	7
pull_request	156	156	158	165	167	167	167	7
Δ	0	-1	0	5	-2	-2	-2	0
Improvement %	0	1	0	-3	1	1	1	0

Retains: results within specified thresholds, fold down for details.

Retains (K) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	150	150	150	150	150	150	150	7
pull_request	150	150	150	150	150	150	150	7
Δ	0	0	0	0	0	0	0	0
Improvement %	0	0	0	0	0	0	0	0

parse canada.toml metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (ms) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	16	17	17	17	17	18	18	59
pull_request	17	17	17	17	18	18	18	58
Δ	1	0	0	0	1	0	0	-1
Improvement %	-6	0	0	0	-6	0	0	-1

Retains: results within specified thresholds, fold down for details.

Retains *	p0	p25	p50	p75	p90	p99	p100	Samples
main	133	134	134	134	134	134	134	59
pull_request	133	134	134	134	134	134	134	58
Δ	0	0	0	0	0	0	0	-1
Improvement %	0	0	0	0	0	0	0	-1

parse twitter.toml metrics

Time (wall clock): results within specified thresholds, fold down for details.

Time (wall clock) (μs) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	2654	2683	2691	2703	2732	2922	3366	363
pull_request	2656	2681	2693	2705	2726	3437	4839	362
Δ	2	-2	2	2	-6	515	1473	-1
Improvement %	0	0	0	0	0	-18	-44	-1

Retains: results within specified thresholds, fold down for details.

Retains *	p0	p25	p50	p75	p90	p99	p100	Samples
main	3138	3139	3139	3139	3139	3139	3139	363
pull_request	3138	3139	3139	3139	3139	3139	3139	362
Δ	0	0	0	0	0	0	0	-1
Improvement %	0	0	0	0	0	0	0	-1