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--show-default-cparams was refused as unknown. It now prints, before compressing, the parameters the level selects for each input, in the reference command's layout (zstdcli.c, printDefaultCParams): name and size, then windowLog .. strategy with upstream's strategy names. It is refused when decompressing and ignored by -b, --train and -l, as there. The selection needed a public entry point: LevelParameters::for_level, the equivalent of ZSTD_getCParams, is the same port the encoder resolves a dictionary-less frame with. The bench-internals facade now goes through it, and the separate zero-means-unknown wrapper is gone. Checked against the system zstd v1.5.7: 216 cases (nine file sizes including an empty file, twelve levels from --fast=5 to -22, with and without a dictionary) print byte-identical output. Part of #128
The post-split block pass ran on Level(16..=22) with a window of at
least 128 KiB, keyed on the level number. Upstream decides it from the
effective cParams (zstd_compress.c, ZSTD_resolveBlockSplitterMode:
strategy >= btopt && windowLog >= 17), so two frames were compressed
worse than they should be:
- a parameter set whose knobs move a lower level onto the optimal band
(level 3 carrying every level-22 knob came out 2.5% larger than
level 22 with the same knobs; zstd --max at the default level lost
1.8% against its own level 22 on z000033);
- levels 13-15 wherever the source size or a dictionary's CDict tier
selects btopt / btultra with a window of 2^17 or more.
The gate now reads the strategy the frame runs. Compressed bytes against
the previous build (identical at every other level on all three shapes):
z000033[..200000] L13 90378 -> 85017 (upstream 85167)
L14 90341 -> 85110 (upstream 83172)
L15 90272 -> 85061 (upstream 82986)
z000033 + dict_tests/dictionary
L13 457425 -> 446171 (upstream 462835)
L14 455233 -> 444172 (upstream 438399)
L15 454769 -> 443924 (upstream 437877)
z000033 (1 MB, no dict) unchanged at L1-L22
The pass is not free. runner1 (x86, no PMU: task-clock), prebuilt
bench-profile binaries interleaved with zstd 1.5.7, three rounds of
perf stat -r 5, ranges not overlapping:
case before after upstream
L13 z000033[..200000] 26.3-26.7 34.3-34.7 26.8-27.8 ms
L15 z000033[..200000] 28.7-29.0 36.6-37.5 34.6-35.7 ms
L13 1 MB + dict 117.4-119.4 149.1-150.9 99.4-102.5 ms
L12 (control, never splits) 19.1-20.0 19.1-19.8 18.8-19.9 ms
The matcher costs the same in both builds; the added time is the split
itself (sub-block size estimates and trial Huffman / FSE table builds),
which levels 16-22 already pay. That cost is its own target.
Carries the regression test a_fully_specified_parameter_set_ignores_the_
base_level (fails before, passes after). The sequence-capture tool, which
cannot follow a post-split frame, now also counts the frame's blocks
against its matcher calls, since a level below 16 can post-split.
Part of #128
The reference command's --max (zstdcli.c, setMaxCompression) replaces the compression parameters wholesale: the largest window, chain, hash and search logs, the smallest minMatch, the longest targetLength, btultra2, and the long-distance matcher at its widest with its hash rate derived. It also unlocks the ultra levels and long-distance matching. A --zstd= list before it is overwritten, one after it adjusts the maximum, as there. Refused on a 32-bit target, as there. One departure: the window stops at 27, the widest this build decodes, where the reference goes to 31; a larger one would write frames this tool cannot open. z000033, against zstd 1.5.7 on the M1: input ours upstream file 426636 B, 2.06 s 426527 B, 4.31 s stdin 426632 B, 1.52 s, 11.5 GB 426527 B, 5.71 s, 17.2 GB peak Part of #128
-B was parsed and dropped. The reference's benchmark (benchzstd.c, BMK_benchMemAdvancedNoAlloc) builds a block table: every input is a frame of its own, cut into -B pieces when the size is at least 32, each compressed independently. Ours compressed all inputs as one stream, so a multi-file benchmark measured a different thing and -B did nothing. - The benchmark now compresses that same block table, one frame per piece, and checks the round trip after measuring. - Frames carry no content checksum, as the reference's benchmark sets none (BMK_initCCtx); the command's --check default does not apply. - The -q header reports the block size asked for, as the reference's. - -B is read like readU32FromChar (a count with K / M); -B0 is none. - The -M accounting sizes the frames buffer as the bound of each piece and the encoder by the widest piece. z000033, -b1 -e5 -B16K -i1, M1, bytes (ours / zstd 1.5.7): L1 512442 / 512274, L2 497291 / 497176, L3 507883 / 491220, L4 476138 / 476388, L5 475162 / 475423. Part of #128
--train-legacy was refused: the reference's original trainer (zdict.c, ZDICT_trainFromBuffer_legacy) had no counterpart here. Library (dict-builder): - dictionary::suffix_array: SA-IS suffix-array construction over u32 positions, alloc only. A suffix array is unique for its text, so it is the array the reference gets from divsufsort. - dictionary::legacy: the trainer itself, following zdict.c: the per-position suffix neighbourhood walk (ZDICT_analyzePos), candidate merging (ZDICT_tryMerge / insertDictItem), selectivity as samples >> s with a floor of 4, the 2000 MiB corpus cap applied a whole sample at a time, and the best-last content layout. - create_legacy_dict_from_slice(samples, sample_sizes, ...) trains and finalizes. It takes the sample sizes because the trainer counts them. CLI: - --train-legacy, --train-legacy=s=# / selectivity=#, and -s#. - The legacy trainer's samples are loaded as dibio.c loads them: files in DiB_shuffle order, each one sample of at most 128 KiB, or cut whole into -B# samples; empty files left out; fewer than five refused; at most 2 GiB, or -M when smaller. Verified against libzstd 1.5.7: - ffi-bench/tests/legacy_trainer_ffi.rs: log lines, the dict_tests unit files and z000033 in 4 KiB samples, selectivity 0/4/9/12, sizes 4 KiB, 16 KiB and 112640 B: the content equals the reference dictionary's, byte for byte, in all 36 cases (only the entropy header differs). - CLI against zstd 1.5.7 on the same file list: identical content with and without -B#, -s#, =s=# and --maxdict. With -r the two walk a directory in different orders (readdir versus sorted), so the shuffle starts from a different list. Training the 16 MB decodecorpus set with -B4096 takes 2.05 s against the reference's 1.24 s on the M1. Part of #128
The legacy trainer spent its time where the reference's does, in the suffix-neighbourhood walk and the suffix-array induction, but paid more for each step: - The shared-prefix count compared a byte at a time; it now compares a word at a time and locates the first differing byte from the XOR, as ZDICT_count does. - Covered runs are marked with one fill rather than a bounds-checked write per position. - The SA-IS induction sweeps index by the bucket layout's invariants instead of checking every access, and reject an empty slot and position 0 with one compare of v - 1 against n. Each invariant is a debug_assert, so the debug suite checks it on every construction. The dictionaries are byte-identical to the previous build's. Part of #128
The induction sweeps follow Yuta Mori's sais.c induceSA: the predecessor's type is decided when a suffix is written, from the neighbouring symbol, and kept in the top bit of the entry, so a sweep no longer reads a separate type array at a random position per suffix; the bucket cursor stays in a register while the symbol does not change. runner1 (x86, task-clock), --train-legacy -B4096 over the 16 MB decodecorpus set, prebuilt bench-profile binaries interleaved with zstd 1.5.7, three rounds of perf stat -r 3: before 3804-3855 ms after 3503-3507 ms zstd 1.5.7 2318-2326 ms Dictionaries byte-identical to the previous build's. Positions now need 31 bits, well above the trainer's 2000 MiB corpus cap. Part of #128
The LMS naming follows sais.c. The sorted LMS positions are compacted to the front of the array, told apart by the type array rather than a rank map; each substring's end is found by a short forward scan; names go to m + p / 2 and are gathered in text order at the back. The per-position rank map (four bytes a position, read at random twice per substring) is gone. A substring reaching the end of the text is taken to be unique, which keeps the comparison inside the text by construction. runner1 (x86, task-clock), --train-legacy -B4096 over the 16 MB decodecorpus set, interleaved with zstd 1.5.7, three rounds of perf stat -r 3: before 3464-3561 ms after 3283-3320 ms zstd 1.5.7 2324-2373 ms Dictionaries byte-identical. The new test sorts 2000 short texts over two and three symbols against the definition; the previous build passes it as well. Part of #128
The trainer copied the whole suffix array into a vector one slot longer at each end, for the two ranks that lead into the noise band. Those ranks are now answered by one compare instead: a negative rank wraps past every real one. The merge scan also reads the eight bytes after the new segment's start once rather than once per table entry, and walks the table as a slice. runner1 (x86, task-clock), --train-legacy -B4096 over the 16 MB decodecorpus set, interleaved with zstd 1.5.7, three rounds of perf stat -r 3: before 3280-3336 ms after 3080-3149 ms zstd 1.5.7 2323-2378 ms Dictionaries byte-identical. Part of #128
Each post-split probe copied its range of sequences, resolved their offsets into the copy, computed every length and offset code, and then had the three table selections compute the codes and count them again: six passes over the range per probe. Upstream codes the block once (ZSTD_seqToCodes) and a probe only counts. - The literal- and match-length codes and a prefix sum of their extra bits are derived once per block beside the existing prefix sums; a probe histograms its slices and reads its extra bits in O(1). - Offsets, the one part that depends on the probe's entry history, are resolved in a single pass without a copy. - The table selection takes the histograms already built. Byte-identical at L1-L22 on z000033[..200000], z000033 and z000033 with dict_tests/dictionary. Also records at the post-split gate that turning the pass off is not a speed lever. runner1 (x86, task-clock), encode_loop_z000033 against ffi_encode_loop_z000033, 50 frames of z000033[..200000], interleaved, three rounds of perf stat -r 3, ms: level before after libzstd L12 (control) 481.6-483.8 481.2-482.3 412.0-413.4 L13 1191-1205 1173-1177 876-880 L15 1288-1300 1263-1280 1187-1202 L16 1982-1987 1948-1954 1626-1637 L19 2919-2947 2867-2874 2358-2377 The probe's own time fell from 7.9% to 3.6% of the L13 profile. Part of #128
Each post-split probe copied the Huffman table it could repeat into a scratch state, let the pricing rewrite that copy, and copied the result again as the state the next probe starts from: two table copies per probe, plus one per block to seed the entry state. The table is never changed in place; a section only keeps it, drops it, or builds a new one. Pricing now reads the previous table by reference and reports which of the three it did. A probe state names its table instead of holding it: the block's entry table borrowed from the compressor, or one a probe built, kept once in the estimator and returned to the weight builder when the block is done. The FSE repeat handles move out of the scratch state rather than being cloned. Byte-identical at L1-L22 on z000033[..200000], z000033 and z000033 with dict_tests/dictionary. Fewer operations, no measurable time change: runner1 (x86, task-clock), 50 frames of z000033[..200000], interleaved with the previous build, three rounds of perf stat -r 3, the ranges overlap at every level (L13 1168-1173 ms against 1169-1175; L12, L15, L16, L19 likewise). Part of #128
Three copies of an FSE encoder table (about 13 KiB each) sat on the entropy path, most visibly under the post-split probes: - every table build cleared all 256 per-symbol entries past the new alphabet, although only what an earlier build wrote there can be non-default; the table now tracks that extent and clears only it - each Huffman weight description built its FSE table by value and moved it into the encoder; the encoder now borrows the table, and the weight builder's scratch keeps one to build into - each probe dropped its build slots and so built every new table on the stack and moved it into a fresh shared handle; handles no probe state holds any more now go to a pool in the estimator workspace, and a probe takes its build slots from it A rebuild into a used table also left an absent symbol's start state and bit width from the earlier build; they are now reset, with a regression test comparing a reused build against a fresh one. Part of #128
The weight description now builds into caller storage, which left the owning builders with no caller in a build without tests, fuzz exports or the dictionary builder, and a dead-code warning on the no-std target.
The weight a price is taken in (integer bit weight, or the fractional one upstream uses from optLevel 1) is a property of the strategy, but it reached the parser as a field of the cost profile. The profile is passed into the per-segment DP by value, so there the field is a runtime bool, and every literal, literal-length and match-length price carried a test on it plus both weight forms. Offset prices already took the mode as the DP's `ACCURATE_PRICE` const. The literal, literal-length and match-length prices, their cached forms and the price-set range kernels now take the mode as a const as well, and the profile no longer carries it. The per-block base-price derivation takes the strategy's constant directly. Byte-identical at L1-L22 on z000033[..200000], z000033 and z000033 with dict_tests/dictionary. runner1 (x86, task-clock), 50 frames of z000033[..200000], interleaved with the previous build and libzstd, three rounds of perf stat -r 3: L13 1121-1127 -> 1096-1101 ms (-2.3%; libzstd 876-880) L19 2820-2827 -> 2752-2760 ms (-2.4%; libzstd 2378-2392) L16 1879-1888 -> 1866-1877 ms (-0.7%, at the noise floor) Controls that never enter the optimal parser: L3 flat, L12 +0.8% (layout), which bounds what the build alone moves. Part of #128
Under the integer weight (btopt) a literal, literal-length or match-length price is one bit scan on a frequency. The per-call price caches stood in for it with a stamp probe, a branch and, on a miss, two stores, which costs as much as the price itself. Upstream computes these prices in place at optLevel 0. The caches now serve only the fractional weight of the btultra strategies. Byte-identical at L1-L22 on z000033[..200000], z000033 and z000033 with dict_tests/dictionary. runner1 (x86, task-clock), 50 frames of z000033[..200000], interleaved with the previous build and libzstd, three rounds of perf stat -r 3: L13 1096-1102 -> 1083-1087 ms (-1.2%; libzstd 875-881) L15 1184-1187 -> 1179-1183 ms (-0.4%; libzstd 1194-1198) Controls: L12 (no optimal parser) and L19 (fractional weight, which this does not touch) flat. Part of #128
The tree insertion walk decoded every node's stored index into an absolute position through four tests (empty slot, below the shift, below the window, past the position) and re-read the table's position base, shift and history start on each node. The collect walk over the same tree already carries the stored index alone: one unsigned range test bounds the window and ends on an empty slot, and the position, history index and pair slot are each one add of a bias taken before the walk. The insertion walk now has the same shape. A slot below the shift cannot reach the range test in an armed block, since a rebase rewrites every slot; that is now a debug assertion rather than a release test. Byte-identical at L1-L22 on z000033[..200000], z000033 and z000033 with dict_tests/dictionary. Fewer operations, no measurable time change: callgrind at L13 (3 frames of z000033[..200000]) puts the insertion function at 48,148,515 -> 47,889,189 instructions; runner1 task-clock, interleaved, three rounds: L13 1080.6-1081.9 -> 1081.1-1082.0 ms, L19 2746-2762 -> 2734-2742 ms, control L12 flat. Part of #128
The optimal parser entered its DP function once per segment, about 16 thousand times per 200 KB frame at level 13, and after each segment walked the segment's plan a second time to replay it into the statistics, re-deriving every offset base through the repeat history. Upstream runs a block as one loop (ZSTD_compressBlock_opt_generic) and records each sequence into the statistics from its traceback. The parser now has the same shape: - one function per kernel runs the whole block: the segment loop around the forward pass and traceback, with the frame, the buffer set-up and the const dispatch paid once per block - the traceback records each settled sequence into the statistics (ZSTD_updateStats) and refreshes the base prices once per segment, so the replay pass is gone; the btultra2 seed pass no longer builds a plan at all - what the pass carries between segments (cursor, pending literals, repeat history, the statistics' literal cursor) lives in the plan buffers rather than in locals, so none of it is live across the segment body. Held as locals it cost the btultra DP about 4.5% more instructions in spills and reloads and measured 1.6% slower at level 16 Byte-identical at L1-L22 on z000033[..200000], z000033 and z000033 with dict_tests/dictionary. callgrind, 3 frames of z000033[..200000]: L13 398,671,808 -> 396,245,242 (-0.61%) L16 635,870,845 -> 636,903,867 (+0.16%) L19 948,388,977 -> 946,328,078 (-0.22%) runner1 task-clock, 50 frames, interleaved with the previous build and libzstd, every arm pinned to one core, two runs: L19 2748-2767 -> 2714-2734 ms (-1.3%, both runs), L13 and L16 unchanged, control L12 flat. Under the 1.5% floor, so not claimed as a speed change. Part of #128
The optimal parser handed its per-position search a query struct: the three repeat offsets, the pending literal count and an optional long-distance candidate, 48 bytes marshalled through memory on every position, and the search merged that candidate into its own result at three exits. Upstream's opt loop calls ZSTD_btGetAllMatches with a pointer to opt[cur].rep and an ll0 flag, and adds the long-distance candidate afterwards (ZSTD_optLdm_processMatchCandidate). The parser now has the same shape: - the search takes `&[u32; 3]` pointing at the node's own repeat history and `ll0: bool`, so nothing is copied per position - the long-distance candidate joins after the search in the parser, through `BtMatcher::push_ldm_candidate` (ZSTD_optLdm_maybeAddMatch); `HcCandidateQuery` survives only as the test entry's argument - the unused `bt_insert_and_collect_matches` dispatcher and its five kernel wrappers are gone (the search body is expanded inside collect), and with them the cost profile's `max_chain_depth` field, which only they read Output changes only with long-distance matching. The search returns early when a repeat or hash3 match reaches the sufficient length or the block end, and the candidate merged inside it was dropped on every such exit; upstream adds it whatever the search did. A regression test covers that case (red on the previous code, green now). --long=27 on 8 MiB of source text, frame bytes before -> after (libzstd), every frame round-trips through libzstd: L16 2,119,499 -> 2,119,471 (2,090,198) L17 2,099,752 -> 2,099,612 (2,065,913) L18 2,087,944 -> 2,087,718 (2,050,924) L19 2,083,481 -> 2,083,409 (2,046,434) L21 2,082,749 -> 2,082,733 (2,045,763) L22 unchanged Byte-identical at L1-L22 on z000033[..200000], z000033 and z000033 with dict_tests/dictionary. callgrind, 3 frames of z000033[..200000]: L13 396,245,242 -> 387,035,914 (-2.32%) L16 636,903,867 -> 625,216,188 (-1.84%) L19 946,328,078 -> 929,011,865 (-1.83%) runner1 task-clock, 50 frames, interleaved with the previous build and libzstd, every arm pinned to one core, three rounds, ranges disjoint: L16 1837-1848 -> 1796-1799 ms (-2.3%), L19 2724-2743 -> 2686-2698 ms (-1.5%), L13 1082-1091 -> 1072-1079 ms (-1.1%, under the 1.5% floor), control L12 flat (483-490 -> 483-484). Part of #128
Before each search the optimal parser inserts the positions it skipped into the binary tree, and it did so with one call per position. Each call re-derived everything that does not depend on the position: the live history slice, the hash and pair table bases with their bounds checks, the pair mask from the chain log, the window floor for the run's target and the coordinate biases, then spilled most of them to the stack before walking a node. At level 13 that prologue was about 170 of the 366 instructions per inserted position, and a catch-up run averages 2.4 positions (130,713 insertions in 53,922 runs over 3 frames of z000033[..200000]). Upstream runs the whole catch-up in ZSTD_updateTree_internal with ZSTD_insertBt1 inlined into its loop, so those values are resolved once per run. The insertion now takes a range, `bt_insert_range(from, stop, end, target)`, and returns the cursor after the last insertion (a long match still carries it past the target, as upstream's `idx += ZSTD_insertBt1(...)` does). Everything position-independent is resolved once per run. Every caller moved over: - the parser's catch-up makes one call per run - `bt_update_tree_until` is one function over the dispatcher instead of five per-kernel copies that existed only to inline the per-position step; a run that may need a rebase still goes one position at a time - the rebase replay inserts its prefix in one call - the sparse incompressible path inserts one position per call, as before Byte-identical at L1-L22 on z000033[..200000], z000033 and z000033 with dict_tests/dictionary, and with --long=27 at L16-L22 on 8 MiB of source text. callgrind, 3 frames of z000033[..200000]: L13 387,035,914 -> 378,521,611 (-2.20%) L16 625,216,188 -> 625,866,312 (+0.10%) L19 929,011,865 -> 929,718,179 (+0.08%) At level 13 the insertion falls 47.9M -> 44.8M and the search 130.6M -> 125.2M. btultra searches nearly every position, so it has almost nothing to catch up (the insertion is 2.2M -> 1.8M at level 16), and its search moves +1.0M from code generation around the call. runner1 task-clock, 50 frames, interleaved with the previous build and libzstd, every arm pinned to one core, two runs of three rounds: L13 1068-1086 -> 1049-1058 ms (-2.0%, disjoint in both runs), L16 1799-1835 -> 1821-1834 ms (overlapping, not established), L19 flat, control L12 flat. Part of #128
Miri cannot execute inline assembly, and the aarch64 prefetch hints are inline assembly, so every test that reaches the dfast matcher (levels 3 and 4) or the decoder's prefetch aborted under Miri on aarch64. Under cfg(miri) the hints now take the portable no-op fallback; a hint has no observable effect, and every other build is unchanged. all_levels_tiny_input_with_hint now runs under Miri with the scalar kernel.
Every price improvement in the optimal parser's forward pass wrote the whole cell: offset, length, literal count and the three repeat offsets of the position the match started from, the last three reloaded from the stack for each write. Those repeat offsets were never read. When the pass reaches a match-ended cell it derives the history from the match's start (the ZSTD_newRep step), overwriting them, and nothing reads a cell ahead of the pass except its offset, length and literal count. Upstream stores the same three fields plus the price (ZSTD_compressBlock_opt_generic) and applies ZSTD_newRep at cur. - `HcOptimalNode::write_match_end` writes offset, length and a zero literal count through field places, leaving the history untouched; the btopt seed and forward loops and every price-set kernel use it, and the kernels lose their `reps` parameter - the two reads of a cell before the pass has derived its history (the match a literal replaces, and the cell the pass is on) read the three fields instead of copying the node, since the arena is uninitialised memory and the history of such a cell may never have been written Byte-identical at L1-L22 on z000033[..200000], z000033 and z000033 with dict_tests/dictionary, and with --long=27 at L16-L22 on 8 MiB of source text. Miri (scalar kernel) passes all_levels_tiny_input_with_hint and btultra2_sparse_skip_matching_preserves_tail_cross_block_match. callgrind, 3 frames of z000033[..200000]: L13 378,521,611 -> 376,366,552 (-0.57%) L16 625,866,312 -> 615,970,215 (-1.58%) L19 929,718,179 -> 911,138,258 (-2.00%) runner1 task-clock, interleaved with the previous build, pinned, three rounds: L13 1045-1052 -> 1037-1041 ms, L19 2677-2711 -> 2659-2664 ms, L16 overlapping, while the L12 control, which never runs this parser, moved by up to 2% between rounds. Under the 1.5% floor: an operation reduction, not a claimed speed change. Part of #128
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In `@ffi-bench/tests/legacy_trainer_ffi.rs`:
- Line 5: Update the Cargo target configuration for legacy_trainer_ffi to
require both bench-internals and dict-builder, so Cargo enables the test when
compiling it with its required features.
In `@README.md`:
- Around line 122-125: Update the `--train-legacy` README description to state
that `-M` caps the samples loaded for legacy training, consistent with
upstream’s `DiB_trainFromFiles`. Narrow the nearby claim that `-M` has no effect
on training so it does not apply to legacy training.
In `@zstd/src/dictionary/legacy.rs`:
- Around line 318-326: Bound the forward and backward suffix-rank walks in the
legacy dictionary logic so they stop at the allocated noise slots instead of
continuing through out-of-range ranks. Apply the same upper-bound stop to the
forward walk in the later length-counting path after its increment; preserve the
existing backward bound there. Keep behavior unchanged for ranks within the
allocated range.
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README.mdffi-bench/Cargo.tomlffi-bench/tests/legacy_trainer_ffi.rszstd/src/bin/structured-zstd/main.rszstd/src/bin/structured-zstd/tests.rszstd/src/decoding/prefetch.rszstd/src/dictionary/legacy.rszstd/src/dictionary/legacy/tests.rszstd/src/dictionary/mod.rszstd/src/dictionary/suffix_array.rszstd/src/dictionary/suffix_array/tests.rszstd/src/encoding/blocks/compressed.rszstd/src/encoding/blocks/compressed/tests.rszstd/src/encoding/bt/mod.rszstd/src/encoding/cost_model/mod.rszstd/src/encoding/cparams.rszstd/src/encoding/fastpath/mod.rszstd/src/encoding/frame_compressor.rszstd/src/encoding/frame_compressor/tests.rszstd/src/encoding/hc/generator.rszstd/src/encoding/hc/optimal.rszstd/src/encoding/hc/priceset.rszstd/src/encoding/levels/fastest.rszstd/src/encoding/match_generator/tests.rszstd/src/encoding/match_table/storage.rszstd/src/encoding/match_table/storage/storage_tests.rszstd/src/encoding/mod.rszstd/src/encoding/opt/types.rszstd/src/encoding/parameters.rszstd/src/encoding/sequence_capture.rszstd/src/encoding/strategy.rszstd/src/fse/fse_encoder.rszstd/src/fse/mod.rszstd/src/fse/tests.rszstd/src/huff0/huff0_decoder/tests.rszstd/src/huff0/huff0_encoder.rszstd/src/huff0/huff0_encoder/tests.rszstd/src/huff0/mod.rszstd/src/lib.rszstd/src/tests/parameters_test.rs
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Every position the optimal parser searched re-derived the binary tree's coordinates from the table: the biases that map a stored index to its absolute position, its history index and its pair slot, the pair mask from the chain log, the position's stored index and its pair slot. That was about thirty instructions of the search's prologue, most of it spilled to the stack straight away, on 353 thousand calls per 3 frames at level 13. All of it follows from the position base, the index shift, the history start and the chain log, none of which moves while an armed block is parsed. Upstream resolves `base` and `btMask` once per call of its whole search. `MatchTable::capture_block_coords` takes them into a `BtCoords` at the start of each block pass, and the search reads the snapshot. Debug builds compare the snapshot with a fresh derivation on every position, and the stored index and pair slot with their table forms, so the whole debug suite checks that nothing moves them mid-block. Byte-identical at L1-L22 on z000033[..200000], z000033 and z000033 with dict_tests/dictionary, and with --long=27 at L16-L22 on 8 MiB of source text. callgrind, 3 frames of z000033[..200000]: L13 376,366,552 -> 369,209,950 (-1.90%) L16 615,970,215 -> 614,154,481 (-0.29%) L19 911,138,258 -> 908,885,890 (-0.25%) runner1 task-clock, interleaved with the previous build and libzstd, pinned, three rounds: L13 1037-1039 -> 1028-1031 ms, L16 1799-1809 -> 1787-1790 ms (both disjoint), L19 overlapping, L12 control 477-483 -> 476-490. Under the 1.5% floor: an operation reduction, not a claimed speed change. Part of #128
Every rank outside the suffix array reads the noise band, and the band is the same 32 bytes on every run. The neighbour walks in `analyze_position` ended only on a short match, so a corpus whose text repeats the band compared equal at every rank past either end and never stopped: `--train-legacy` and `create_legacy_dict_from_slice` hung on it. The reference reads past its two slots there, so it defines no result to keep. The forward walks now stop at the upper slot (the counting walk still counts it, as the reference does) and the backward walk at rank 0; on every other corpus the slot holds noise that ended the walk anyway. Carries neighbour_walks_stop_at_the_noise_slots, which runs a walk off the array over a corpus that is the band itself: it hung before the fix and passes after. The band's generator is split out for it. The dictionaries are unchanged: legacy_trainer_ffi matches libzstd's content in all its cases, and --train-legacy -B4096 over decodecorpus_files writes the same bytes. callgrind on 40 of those files: 12,959,833,409 -> 12,949,794,330 instructions. Part of #128
…oc links - README: `-M` caps the samples `--train-legacy` loads, as the reference's command hands its memory limit to `DiB_trainFromFiles`; the claim that it describes nothing is narrowed to compressing and listing. The call site says why the limit is passed. - The dictionary parity targets against libzstd (`dictionary_ffi`, `legacy_trainer_ffi`) need `dict-builder` as well as `bench-internals`, and CI ran ffi-bench with `bench-internals` alone, so both compiled to nothing there. Both now require the two features and CI enables them. - Two intra-doc links in `compressed.rs` pointed at a renamed function and at a test-only one, failing rustdoc with private items. Part of #128
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In `@zstd/src/dictionary/legacy/tests.rs`:
- Around line 16-18: Expand the fixture around analyze_position to include four
matching suffix ranks, such as four noise_band() entries, so execution passes
the MIN_RATIO check and reaches the second neighbour walk. Assert that
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structured-zstd/zstd/src/bin/structured-zstd/main.rs
Lines 1193 to 1196 in ce2eeaf
Apply --block-size to chunked modes
When --block-size=64K is used with benchmark or legacy-training mode, this arm validates the value and discards it, so opts.block_size remains None and the input is processed without chunking; the equivalent -B64K spelling does assign the field. This also conflicts with the help text that groups -B# and --block-size=# as no-ops only when compressing. Store the parsed value here so both spellings behave consistently.
structured-zstd/zstd/src/encoding/blocks/compressed.rs
Lines 1865 to 1866 in ce2eeaf
Reuse default FSE tables on no-atomic targets
On targets without pointer atomics or the critical-section feature, each qualifying post-split block deep-clones all three boxed default FSE tables here; each table is roughly eleven kilobytes, so this adds three allocations and about 33 KiB of copying per block even though the defaults are read-only. Borrow the defaults or retain them in the estimator scratch instead of rebuilding owned copies for every block.
AGENTS.md reference: AGENTS.md:L35-L38
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The legacy trainer copied every sample into one buffer followed by the noise band, as the reference does. The corpus now borrows the samples and keeps the band beside them; the accessors join the two, with the reads that cross into the band out of line. The word loop in `common` reads unaligned words through a raw pointer. Through a slice index each word paid a bound test, because the loop limit does not prove every index in range; the owned version paid an overflow test per word for the same reason. Those tests, not the borrow, were what made an earlier borrowed version measure slower. --train-legacy -B4096 over decodecorpus_files, runner1 (load 0.03), bench profile, three interleaved rounds pinned to one core: - wall time 15.92-15.97 s -> 8.92-9.14 s - max RSS 251 MB -> 235 MB - dictionary bytes identical (md5 857c43bb70a0abeaf5e1bc28e8479edd) - zstd 1.5.7 in the same session: 7.45-7.58 s, 181 MB, so 2.1x -> 1.2x legacy_trainer_ffi still matches libzstd's content in every case, and the legacy tests pass under Miri. Part of #128
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The SA-IS construction held, beside the array itself, a byte per position for the suffix types, the LMS positions, a copy of the reduced string, the reduced string's own array and the sorted LMS positions, and four bucket tables per level. In the recursion the alphabet is the number of names, so the tables alone came to millions of entries per level. Under the legacy trainer this made the construction, not the analysis, the peak of the whole run. It is now laid out as Yuta Mori's sais.c lays it out: the reduced string is gathered at the back of the array and sorted recursively into the front, the LMS positions are recomputed from the text into the reduced string's slots once it is sorted, and placed at their buckets' ends in place. Two bucket tables per level (counts and a cursor), the types a bit per position, and no recursion at all when every name is distinct, since the names are then the order. --train-legacy -B4096 over decodecorpus_files, runner1 (load 0.56), bench profile, three interleaved rounds pinned to one core: - max RSS 235 MB -> 166 MB (zstd 1.5.7: 181 MB) - wall time 8.91-9.00 s -> 8.59-8.65 s - dictionary bytes identical (md5 857c43bb70a0abeaf5e1bc28e8479edd) massif before: peak 243 MB during the construction, 38 MB of it the first recursion level's bucket tables. 166 MB is what the analysis holds (samples, suffix array, rank array, marks: ten bytes a position), so the construction no longer sets the peak. legacy_trainer_ffi still matches libzstd's content in every case. Part of #128
Each step of an induction sweep reads the text before the suffix it takes, at a position the order of the array makes random, and in the recursion also the cursor of that symbol's bucket, whose table has as many entries as there are names. Both miss the cache on a large corpus, and the sweeps are most of the construction. The sweeps now warm them ahead, as libsais does: the text for the entry 64 slots ahead, and, where the symbols are the recursion's names, the bucket cursor for the entry 32 ahead, whose symbol that earlier prefetch has brought in. The symbol read is clamped, so an entry not yet written or not live costs a wasted hint, never an out-of-range read. --train-legacy -B4096 over decodecorpus_files, runner1 (load 0.75), bench profile, three interleaved rounds pinned to one core: - wall time 8.33-8.54 s -> 7.78-7.88 s (zstd 1.5.7: 7.45-7.58 s) - max RSS unchanged (166 MB) - dictionary bytes identical (md5 857c43bb70a0abeaf5e1bc28e8479edd) Part of #128
The legacy trainer analyses every text position in order, and each analysis starts from the position's rank, which is random: the suffix array around that rank and the text of the two neighbours there miss the cache every time. Those loads were most of the trainer's time, as they are of the reference's. The loop now warms them ahead of reaching a position: the array line around the rank of the position 16 on, and the neighbours' text for the position 8 on, whose array line that earlier hint has brought in. Positions the loop then skips cost a wasted hint. --train-legacy -B4096 over decodecorpus_files, runner1 (load 0.75), bench profile, three interleaved rounds pinned to one core: - wall time 7.77-7.92 s -> 7.29-7.38 s - zstd 1.5.7 in the same session: 7.35-7.39 s against our 7.22-7.35 s - dictionary bytes identical (md5 857c43bb70a0abeaf5e1bc28e8479edd) - distances of 32 and 16 measured the same as 16 and 8 Part of #128
Each level of the suffix-array recursion allocated its two bucket tables, as long as its alphabet, which there is the number of names: tens of megabytes on a large corpus, allocated and freed before the analysis starts. glibc returns such blocks to the system; macOS keeps them resident, so they stayed in the trainer's peak there. The tables now go in the free slots between a level's reduced string and its sorted front, as sais.c places them: a level reduced to m symbols leaves n - 2m slots there. A level whose tables do not fit still allocates them; the top level, with 256 symbols and no free slots, always does. --train-legacy -B4096 over decodecorpus_files, dictionary bytes identical (md5 857c43bb70a0abeaf5e1bc28e8479edd) on both hosts: - M1: max RSS 203 MB -> 184 MB (zstd 1.5.7: 186 MB) - runner1: max RSS unchanged (166 MB), wall time 7.24-7.30 s -> 7.19-7.22 s, three interleaved rounds, below what a rebuild resolves Part of #128
The analysis measures how long the prefixes of suffix-order neighbours agree, and on a corpus with long repeats those comparisons run for many words: callgrind put the word loop at 48 of the trainer's 59 billion instructions on decodecorpus_files, against 40 billion for the whole of the reference's analysis. The loop tested its bound on every word, where the reference relies on the noise band instead. The comparison now goes through the crate's common-prefix kernel, resolved once per run (AVX2, SSE, NEON or scalar), for the part of both runs inside the samples; the band is still read a byte at a time past their end. --train-legacy -B4096 over decodecorpus_files, dictionary bytes identical (md5 857c43bb70a0abeaf5e1bc28e8479edd) on both hosts: - runner1 (AVX2, load 3.5 from another job), three interleaved rounds pinned to one core: 7.18-7.23 s -> 5.90-5.94 s (zstd 1.5.7: 7.35-7.39 s) - M1 (NEON), one round: 5.00-5.06 s -> 4.91 s, 60.4 -> 53.4 billion instructions, 12.17 -> 11.59 billion cycles (zstd: 4.35-4.67 s) Part of #128
The NEON common-prefix loop took 16 bytes a step and tested each eight-byte half of the equality mask with its own lane move, compare and branch, which made it little cheaper per byte than the scalar word loop. Once the legacy dictionary trainer compared its long repeats through it, M1 ran 53 billion instructions to the reference's 31. A step now compares 32 bytes and branches once: the two equality masks are joined and their minimum lane tested. The mismatch is located only on the step that has one, from a nibble-per-byte mask narrowed out of the equality result. A lone 16-byte step handles what the loop leaves before the scalar tail, so the result is the same byte count as before on every input. Carries neon_prefix_len_matches_scalar_at_every_mismatch_position, which checks every length up to 100 and every mismatch position in it against the scalar kernel. M1, --train-legacy -B4096 over decodecorpus_files, two interleaved rounds, dictionary bytes identical: - 53.3 -> 38.5 billion instructions, 11.62-11.75 -> 10.19-10.24 billion cycles (zstd 1.5.7: 10.6-10.8 billion), 4.96-5.98 s -> 4.19-4.41 s M1, encode_loop_z000033 level 19, 4 frames, three interleaved rounds, same output: 4.17 -> 4.15 billion instructions, 1.594-1.624 -> 1.548- 1.580 billion cycles. Part of #128
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- `--max` tests assumed a 64-bit target; on 32-bit the command refuses it, as the reference does, so those tests are 64-bit only and a 32-bit test checks the refusal. - A benchmark input that shrank between being sized and being read was accepted short, and the frames, cut at the recorded sizes, panicked in `split_at`. Any change of size is now an error. Carries a_benchmark_input_that_shrank_is_refused. - Training file sizes under `-B` were summed unchecked, so sparse files reporting huge lengths wrapped the totals into a small training set. The sums stop at the top of the range, which the loader's cap then cuts. Carries training_sizes_past_the_integer_range_do_not_wrap. - Under `-M` the benchmark listed every frame just to weigh them before the limit could refuse the run; the room and the widest frame are now worked out per file from its whole blocks and its tail. Carries the_frame_extent_matches_the_frames_it_describes. - The legacy trainer's measuring walk gets its own noise-slot test, which hangs with that walk's bound removed. - Split probes no longer take three FSE table handles each: the tables a probe may repeat are borrowed from the state it starts from, and a handle is taken only for a repeated table the next state keeps. The arena for the probes' Huffman tables is kept across blocks instead of allocated per block. The optimal parser's segment loop bounds itself once per block. Frames are byte-identical at L1-L22 on z000033[..200000], z000033, z000033 with dict_tests/dictionary, and --long at L16-L22 (73 checks). runner1, 50 frames of z000033[..200000], interleaved: L16 1785-1808 -> 1768-1792 ms, L19 2640-2693 -> 2647-2680 ms, control L3 219-224 -> 219-221 ms, within what a rebuild resolves; the segment loop bound alone L16 1762-1792 -> 1759-1761 ms with L3 moving the same. Fewer operations, no measurable time change. Part of #128
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In @zstd/src/bin/structured-zstd/main.rs:
- Around line 3493-3524: Update the training sample loading flow associated with
training_extent so the load budget accounts for the per-sample sizes metadata,
or reject a block_size whose sample count exceeds that budget before opening or
reading files. Preserve the existing corpus cap while ensuring -B1 cannot
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- The benchmark listed one length per frame after the `-M` check, a word a frame that the ceiling never counted: 512 MiB for `-B32` over 2 GiB. The frame lengths are now yielded from the same arithmetic layout instead of collected. - Training samples were loaded against a budget for their bytes alone, while each one also records its length in a word: under `-B1` the list was eight times the bytes. The budget now holds both, and the list is sized from it. Carries training_sample_sizes_count_against_the_budget, which fails without the change (64 bytes and 64 sizes against a 200-byte budget). - The legacy trainer's prefix comparison tested a subtraction that cannot underflow on every call: every position it is given is a suffix or the noise slot. The invariant is a debug assertion now. - The legacy trainer finalizes with every sample on purpose, as the reference does; the call says so. - The NEON prefix kernel records the measurements behind it. Part of #128
unwrap_err needs the Ok type to be Debug, which Options is not, so the i686 test target did not compile. The refusal is matched with let-else instead. Part of #128
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- The samples buffer and the list of their lengths each reserved room from the whole budget, so under -B1 the two together reserved close to twice it. They are now split from it: a sample holds at most one piece and costs one entry, which bounds the bytes at piece / (piece + entry) of the budget and the entries at one per whole piece plus one per file. - A block size near u64::MAX overflowed the budget arithmetic (a sample's cost, and the check of a piece against what is left). The cost is computed in u128 and the check compares without adding the piece. Carries a_block_size_at_the_top_of_the_range_loads_whole_files, which panicked on the overflow. - The training totals were summed with saturation, which turned the sample count into "many" instead of a count once it overflowed. They are summed exactly in u128. - The optimal parser's segment loop ran to `len.saturating_sub(8)`; it now tests `cursor + 8 < len`, which needs no floor because the cursor never passes the block's end. Frames are identical by construction; runner1, 50 frames of z000033[..200000], interleaved: L16 1766-1780 -> 1768-1792 ms, L19 2617-2660 -> 2610-2638 ms, control L3 flat. training_sample_sizes_count_against_the_budget now also checks the reserved room, and failed on the previous reservations (64 bytes of room and 22 entries against a 200-byte budget). Part of #128
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--block-size=# was parsed and dropped, while the reference reads it into the same setting as -B# (zstdcli.c, `--block-size` with NEXT_TSIZE and `-B` into `blockSize`). So a benchmark or a training run given the long spelling cut nothing and fell back to whole files or 128 KiB samples. It now sets the block size as -B does, zero meaning none. Carries the_long_block_size_sets_what_b_sets, which failed before the change. The file shuffle used for training records that it is the reference's DiB_shuffle step for step. Part of #128
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Summary
The remaining single-threaded pieces of the command-line surface, the legacy dictionary trainer behind one of them, and a round of work on the optimal parser (levels 13-22) and the post-split entropy path.
Command line
--show-default-cparamsprints the parameters a level selects for each input, in the reference command's layout. It rests on a new publicLevelParameters::for_level, the counterpart ofZSTD_getCParams. Checked against zstd 1.5.7 on 216 cases (nine sizes, twelve levels, with and without a dictionary): byte-identical output.--maxsets every knob to its hardest end, as the reference'ssetMaxCompressiondoes. The one departure is the window, which stops at 27, the widest this build decodes.-B#in benchmark mode cuts inputs into independent frames, the block table ofbenchzstd.c. It was parsed and dropped before.--train-legacy,--train-legacy=s=#and-s#use a new legacy trainer (dictionary::legacy, SA-IS suffix array,zdict.clayout). On 36 cases the dictionary content is byte-for-byte the reference's; only the entropy header differs.Legacy trainer performance
The trainer borrows the samples instead of copying them, builds the suffix array in place as
sais.cdoes (the reduced string at the back of the array, the recursion's bucket tables in its free slots), prefetches ahead of the induction sweeps and of the analysis, and compares prefixes through the vector common-prefix kernel. The NEON kernel now compares 32 bytes a step with one branch, which the encoder shares.--train-legacy -B4096over the 16.6 MB decodecorpus set, interleaved with zstd 1.5.7, identical dictionary on both hosts:The NEON kernel change leaves encoder output unchanged;
encode_loop_z000033at level 19 on M1 runs 1.548-1.580 G cycles against 1.594-1.624 G before.Encoder fix
ZSTD_resolveBlockSplitterModedoes, rather than onLevel(16..=22). z000033[..200000] at L13-L15 is 5.9% smaller, and a knob set that moves a low level onto the optimal band is no longer worse than the level it copies. A regression test is included.Performance, levels 13-22
Each commit carries its own before/after numbers. The structural changes bring the parser to upstream's shape:
ZSTD_compressBlock_opt_generic);ZSTD_optLdm_processMatchCandidate);ZSTD_updateTree_internal);On the entropy side, FSE tables are built in place, split probes borrow the Huffman table, and split-probe length codes are derived once per block.
runner1 (x86, task-clock), 50 frames of z000033[..200000], same-boundary harnesses interleaved with libzstd:
Output is byte-identical at L1-L22 on z000033[..200000], z000033 and z000033 with
dict_tests/dictionary, with two exceptions:Test infrastructure
cfg(miri)the aarch64 prefetch hints become no-ops, so Miri can run any encoder level. This matters because the optimal parser's node arena is uninitialised memory.Testing
cargo nextest run --workspace --features hash,std,dict-builder: all pass on aarch64 (M1) and on x86 (runner1).ffi-benchdictionary cross-checks against libzstd (legacy_trainer_ffi,dictionary_ffi) on both hosts.cargo clippy --workspace --all-targets --features hash,std,dict-builder -D warningson both architectures;-p ffi-bench --features bench-internals,dict-builder;wasm32-unknown-unknownwith+simd128.cargo check --target thumbv7em-none-eabihf --no-default-features,cargo fmt --check,cargo test --doc, and rustdoc with-D warnings.all_levels_tiny_input_with_hint,btultra2_sparse_skip_matching_preserves_tail_cross_block_match,hc_ldm_candidate_survives_the_search_early_exit, the suffix-array tests and the light legacy-trainer tests.Part of #128
Summary by CodeRabbit
New Features
--maxcompression settings and--show-default-cparamsto display default compression parameters.-B; benchmarks measure separate frames per input file or chunk and verify round-trip results.Documentation