{ "number": 35041, "repo": "bitcoin/bitcoin", "url": "https://github.com/bitcoin/bitcoin/pull/35041", "title": "descriptor: speed-up `Parse` (xpub/xpriv) in ~30%", "author": "brunoerg", "author_association": "MEMBER", "created_at": "2026-04-09T18:19:20Z", "updated_at": "2026-09-17T03:03:06Z", "age_days": 160, "draft": false, "labels": [ "Descriptors" ], "milestone": null, "base": "master", "head_sha": "ddcacd25e735dad4868bab7f618961a363f23239", "head_ref": "2026-04-descriptor", "head_repo": "brunoerg/bitcoin", "head_history": [ { "t": "2026-06-10T15:50:16Z", "sha": "0d8110a13579cee43b4d77bdbad943cc821cd6cb" }, { "t": "2026-06-10T17:51:54Z", "sha": "6dd023abbc9a1d8ece5dc9f9e186e7f5b1fb6f91" }, { "t": "2026-08-24T14:27:12Z", "sha": "0339b33e41f13f87111c2e03e1ddc42bc6a596c4" }, { "t": "2026-09-02T01:02:59Z", "sha": "ddcacd25e735dad4868bab7f618961a363f23239" } ], "additions": 67, "deletions": 28, "changed_files": 5, "commit_count": 2, "size_bucket": "S", "mergeable_state": "clean", "bot": { "drahtbot": { "present": true, "reviews": { "ack": [ { "login": "hodlinator", "url": "https://github.com/bitcoin/bitcoin/pull/35041#pullrequestreview-5086723970" } ], "concept_ack": [ { "login": "sedited", "url": "https://github.com/bitcoin/bitcoin/pull/35041#pullrequestreview-4445194698" } ] }, "conflicts": [ { "number": 36133, "title": "wallet: store multipath descriptor", "author": "Sjors" } ] } }, "acks_parsed": { "sedited": { "kind": "concept_ack", "hash": null, "t": "2026-06-07T14:04:32Z", "stale": false }, "hodlinator": { "kind": "ack", "hash": "ddcacd25e735dad4868bab7f618961a363f23239", "t": "2026-09-02T07:29:39Z", "stale": false } }, "acks_tally": { "ack": 1, "stale_ack": 0, "concept_ack": 1, "approach_ack": 0, "nack": 0, "concept_nack": 0, "approach_nack": 0 }, "reviews": { "approved": 1, "changes_requested": 0, "distinct_reviewers": [ "hodlinator", "l0rinc", "maflcko", "sedited" ] }, "signals": { "needs_rebase": false, "ci_failed": false, "mergeable_state": "clean", "last_author_activity": "2026-09-02T01:07:31Z", "last_reviewer_activity": "2026-09-02T07:29:39Z", "last_reviewer": "hodlinator", "author_silent_days": 15, "waiting_on_author_days": 15, "days_since_update": 0 }, "refs": { "mentioned": [], "depends_on": [], "fixes": [], "linked_issues": [], "references": [], "conflicts": [ 36133 ] }, "stack": { "shares_commits_with": [], "based_on": [], "base_for": [] }, "review_paths": [ "src/base58.cpp", "src/key_io.cpp", "src/script/descriptor.cpp" ], "body": "This PR speeds up descriptor parsing, for basically descriptors that use xpub/xpriv, through some targeted improvements (I've been working on fuzz targets for wallet stuff for a while. I've noticed that some of them are slow so I started to work on understanding why and improve what can be improved. The finding came from it):\n\n- Avoid redundant base58 decoding when parsing extended keys (this is the major improvement)\n\n ParsePubkeyInner unconditionally called both DecodeExtKey() and DecodeExtPubKey(), each running a full DecodeBase58Check (two SHA256 passes over ~111 bytes). A new DecodeExtKeyOrPubKey() function performs a single base58 decode and then checks the prefix, halving the cryptographic work per key. The interfaces of DecodeSecret, DecodeExtKey, and DecodeExtPubKey are also updated to accept string_view instead of const std::string&, eliminating unnecessary string copies in the descriptor parser and allowing DecodeBase58/DecodeBase58Check to use pointer-range iteration instead of strlen.\n\n- Replace O(n) charset lookup with precomputed table\n\n DescriptorChecksum previously called std::string::find() for every character in the descriptor string, doing up to 96 comparisons per character. This replaces it with a 256-entry precomputed lookup table for O(1) lookups. The benefit scales with descriptor length.\n\n-----------\n\n`Parse()` with the following descriptor:\n```sh\ntr(xpub6CGCzpvrZVssNNXuP1Awcz8GoakYyJHra2WHASXfCzsD9szbQFoT1pLMdQopyqaSqXUprH7fkk8NG2pUbQa5HpNzpWmEsdNZDHxXvSLPTrn/*,{{multi_a(20,xpub6CGCzpvrZVssNNXuP1Awcz8GoakYyJHra2WHASXfCzsD9szbQFoT1pLMdQopyqaSqXUprH7fkk8NG2pUbQa5HpNzpWmEsdNZDHxXvSLPTrn/*,xpub6C5MW95EE8hAmxm96LdAFYkweaAktQoojCf2MwJmNL9Fi6oUPeBnpFdEzhs9zHwr4HQEeF1r1yAUR8MqDJqk4YPteh75rNoCKCtud7shDDk/*,xpub6DNEUJP1zLAZ1P6gYRba9FyxuppmkrPmSKz3FLM7msRwn2LEr4LnKfAnNoSoAbnbW2orTfsitdfWTxLbJCZ6LizqV7cFUavSAjWzNjqdfCP/*,xpub6Cm5sAgCZQvYtnatYPdFuLhsD9VtgY3Rtt48TrdgqXm4DttXfM6nFmFTko8KcyGhPswTvPcTzfpMUvqV3F9tgLPvzfzoKwjmU668vBmGXEX/*,xpub6DN66R61Luv95HLvznR2ZWsbYuGBoK9LDR6XiNm1pvp5zRJ2vFhLQ4PBe2pDn59sKmRnEFbdLtBVZFN3QAujcGZ5PomGCvrnisxkP2fcgHg/*,xpub6D2GtAtYodmjwEoAzorKUta44NDvAB4JjafYXxsQ5hTWvCAK55nnkyNHfdjrsx3umfgGe1nnHut13mLuFqqi2fs7VVyv6rht76ddrDGhrTY/*,xpub6Bfi8jsDMuu2XHQ1TGRB6ehjdHKKmTwRFQYU6QcgHoZswqbzKsXs9Qd87nAxevjZwuQ37jaVnQoPF6wY34BJoeLxXkEYMpKz2CBHLcEmJVF/*,xpub6CYiNdQesStiBwZkWjPBxwxxf6oPMH9meBMujCwBX74X8nCpMF9zRZUbDrU9raQah1LQcnzLQrHC6Kr6LNCmsBpaMkYD3U6FyhHZfTHQGUB/*,xpub6CddszJHLa3VisZ6ufU4hiFcGsuuPHo7hYa24o3kPuPfAbMED4ajuDa6svuqxxBxYgUQhN8LK7MtTMetquNo7YsWhiV8hX2gBfjszJVXgkG/*,xpub6DAM262AxC4Um3rxBiP5FoA7SJJG3a7MjaJkEyXWyMA6iNuyqWueKZHSSNjKEWnn8Wi3PUQNTV1Z3a59C2Qaidha88GTWtAMhJBAWBBvuTN/*,xpub6ByZcsLsr8xTCJmYxvLpLrsFzuHNXRLR4xMyB9ZFLek1hDVh7zba2xAVTU8M6eonFFAAPYpTA76bDuopF5zyBkZqFc3rtJ3ziH1BUXkjC6j/*,xpub6Bx2LErujvR1noXrk7RHQB9htiDcPM5qYuV7Jg1nZh5jWeK8pYB4DnYQ73EX9sB9M6rnNsF8LDPUejHiXrBx2JJQSdVQ9i9FfEzJLuAnzEd/*,xpub6DSBog1uLngjBWVDUpLTQ19jGGKovgc3iTd1ijL4fjk9sgNqrnG5kGLjUWncay2jbqdgt6yrbYSHhfwsTMp7i8pUD1FMCQuFyqdsZpgUNH8/*,xpub6C53ov8LpuGp5MM4ghqUFJcdTnXJCRHyXaz1RVCys2uQErpdzUWHtm8Bsg8NJyaqfhGWvm9WPSE7jMneCRw1xs1CTajpToXyRqSCc41JiuY/*,xpub6CscWPNXdEybbJVvx7fJTrfHyTkKZtb97qcpQ9fH4k4xtm4nkckSpvy86heQsdyoF28CugwLHg5kLDwpGoPQAYXQ3RG9cJB2Na1FdeN1wt5/*,xpub6Cmrivt6w3kVAxw7NmcKSY19gSLmC2tVwx46cdigr9d1UEnttJCGZJ7NQu1MkugpZgF9rQ3j3NKUiZ2MoaC2QoZUfi4nwxbpH39SQZaBHut/*,xpub6D1Ey5JAYnBxFE8i2V2SUsEpJt7r3ykJKcShcpT2xN9CXtVQy5dKeYiZ9D1bdnkPrmgEajrSuA5nWqf94s6u7FwvXy3cU4BXUMgAt9C8wGT/*,xpub6CwJ2vicnoSJNFDzhonucHNVHDwyb1vyiu2VF6zmjQrzGb4qoAma1i2QJ7qRNe1qmpvvWwzSuQDgMnCECFQhZaPKuPFjcMo33r2xenBauxf/*,xpub6CiLNz8mFB4fB51x6gMNu44Up9PyVhq7fSxQb8UzYQermvMShwWyqzQe99Uiyxpfy1ow42xUGpPGBHf8ErxDbQojBf7Uy7hKFgYk8KpgMm2/*,xpub6DQ2qVMZ2o2QGGpYDsw5hpAcygNVEycAkkCib2Lexwm8gYWMCSecZ256AbAV93Rgze6h8yEoTcqUnvnz7L69WUqp7cXd85X8HoeKWjPHRRZ/*),multi_a(20,xpub6CGCzpvrZVssNNXuP1Awcz8GoakYyJHra2WHASXfCzsD9szbQFoT1pLMdQopyqaSqXUprH7fkk8NG2pUbQa5HpNzpWmEsdNZDHxXvSLPTrn/*,xpub6C5MW95EE8hAmxm96LdAFYkweaAktQoojCf2MwJmNL9Fi6oUPeBnpFdEzhs9zHwr4HQEeF1r1yAUR8MqDJqk4YPteh75rNoCKCtud7shDDk/*,xpub6DNEUJP1zLAZ1P6gYRba9FyxuppmkrPmSKz3FLM7msRwn2LEr4LnKfAnNoSoAbnbW2orTfsitdfWTxLbJCZ6LizqV7cFUavSAjWzNjqdfCP/*,xpub6Cm5sAgCZQvYtnatYPdFuLhsD9VtgY3Rtt48TrdgqXm4DttXfM6nFmFTko8KcyGhPswTvPcTzfpMUvqV3F9tgLPvzfzoKwjmU668vBmGXEX/*,xpub6DN66R61Luv95HLvznR2ZWsbYuGBoK9LDR6XiNm1pvp5zRJ2vFhLQ4PBe2pDn59sKmRnEFbdLtBVZFN3QAujcGZ5PomGCvrnisxkP2fcgHg/*,xpub6D2GtAtYodmjwEoAzorKUta44NDvAB4JjafYXxsQ5hTWvCAK55nnkyNHfdjrsx3umfgGe1nnHut13mLuFqqi2fs7VVyv6rht76ddrDGhrTY/*,xpub6Bfi8jsDMuu2XHQ1TGRB6ehjdHKKmTwRFQYU6QcgHoZswqbzKsXs9Qd87nAxevjZwuQ37jaVnQoPF6wY34BJoeLxXkEYMpKz2CBHLcEmJVF/*,xpub6CYiNdQesStiBwZkWjPBxwxxf6oPMH9meBMujCwBX74X8nCpMF9zRZUbDrU9raQah1LQcnzLQrHC6Kr6LNCmsBpaMkYD3U6FyhHZfTHQGUB/*,xpub6CddszJHLa3VisZ6ufU4hiFcGsuuPHo7hYa24o3kPuPfAbMED4ajuDa6svuqxxBxYgUQhN8LK7MtTMetquNo7YsWhiV8hX2gBfjszJVXgkG/*,xpub6DAM262AxC4Um3rxBiP5FoA7SJJG3a7MjaJkEyXWyMA6iNuyqWueKZHSSNjKEWnn8Wi3PUQNTV1Z3a59C2Qaidha88GTWtAMhJBAWBBvuTN/*,xpub6ByZcsLsr8xTCJmYxvLpLrsFzuHNXRLR4xMyB9ZFLek1hDVh7zba2xAVTU8M6eonFFAAPYpTA76bDuopF5zyBkZqFc3rtJ3ziH1BUXkjC6j/*,xpub6Bx2LErujvR1noXrk7RHQB9htiDcPM5qYuV7Jg1nZh5jWeK8pYB4DnYQ73EX9sB9M6rnNsF8LDPUejHiXrBx2JJQSdVQ9i9FfEzJLuAnzEd/*,xpub6DSBog1uLngjBWVDUpLTQ19jGGKovgc3iTd1ijL4fjk9sgNqrnG5kGLjUWncay2jbqdgt6yrbYSHhfwsTMp7i8pUD1FMCQuFyqdsZpgUNH8/*,xpub6C53ov8LpuGp5MM4ghqUFJcdTnXJCRHyXaz1RVCys2uQErpdzUWHtm8Bsg8NJyaqfhGWvm9WPSE7jMneCRw1xs1CTajpToXyRqSCc41JiuY/*,xpub6CscWPNXdEybbJVvx7fJTrfHyTkKZtb97qcpQ9fH4k4xtm4nkckSpvy86heQsdyoF28CugwLHg5kLDwpGoPQAYXQ3RG9cJB2Na1FdeN1wt5/*,xpub6Cmrivt6w3kVAxw7NmcKSY19gSLmC2tVwx46cdigr9d1UEnttJCGZJ7NQu1MkugpZgF9rQ3j3NKUiZ2MoaC2QoZUfi4nwxbpH39SQZaBHut/*,xpub6D1Ey5JAYnBxFE8i2V2SUsEpJt7r3ykJKcShcpT2xN9CXtVQy5dKeYiZ9D1bdnkPrmgEajrSuA5nWqf94s6u7FwvXy3cU4BXUMgAt9C8wGT/*,xpub6CwJ2vicnoSJNFDzhonucHNVHDwyb1vyiu2VF6zmjQrzGb4qoAma1i2QJ7qRNe1qmpvvWwzSuQDgMnCECFQhZaPKuPFjcMo33r2xenBauxf/*,xpub6CiLNz8mFB4fB51x6gMNu44Up9PyVhq7fSxQb8UzYQermvMShwWyqzQe99Uiyxpfy1ow42xUGpPGBHf8ErxDbQojBf7Uy7hKFgYk8KpgMm2/*,xpub6DQ2qVMZ2o2QGGpYDsw5hpAcygNVEycAkkCib2Lexwm8gYWMCSecZ256AbAV93Rgze6h8yEoTcqUnvnz7L69WUqp7cXd85X8HoeKWjPHRRZ/*)},{multi_a(20,xpub6CGCzpvrZVssNNXuP1Awcz8GoakYyJHra2WHASXfCzsD9szbQFoT1pLMdQopyqaSqXUprH7fkk8NG2pUbQa5HpNzpWmEsdNZDHxXvSLPTrn/*,xpub6C5MW95EE8hAmxm96LdAFYkweaAktQoojCf2MwJmNL9Fi6oUPeBnpFdEzhs9zHwr4HQEeF1r1yAUR8MqDJqk4YPteh75rNoCKCtud7shDDk/*,xpub6DNEUJP1zLAZ1P6gYRba9FyxuppmkrPm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PR:\n```sh\n| ns/op | op/s | err% | total | benchmark\n|--------------------:|--------------------:|--------:|----------:|:----------\n| 90,253.50 | 11,079.90 | 0.2% | 0.01 | `ParseDescriptor`\n```\n\nMaster:\n```sh\n| ns/op | op/s | err% | total | benchmark\n|--------------------:|--------------------:|--------:|----------:|:----------\n| 127,812.50 | 7,823.96 | 0.5% | 0.01 | `ParseDescriptor`\n```\n\nI didn't put the benchmark itself here but if reviewers think worth, I can do it.\n\n--------\n\nJoint work with claude \ud83d\ude05", "commits": [ { "sha": "59daebcf05db41d83f9d1974b5c79be3eaf62770", "date": "2026-09-02T00:10:16Z", "message": "descriptor, key_io: avoid redundant work when parsing keys\n\nIn ParsePubkeyInner, every extended key required two full base58\ndecodes: once via DecodeExtKey and again via DecodeExtPubKey, even\nthough at most one can succeed. Replace both calls with a new\nDecodeExtKeyOrPubKey helper that performs a single DecodeBase58Check\nand dispatches on the 4-byte version prefix to populate either the\nxprv or xpub result.\n\nAlso eliminate the per-key std::string allocation in ParsePubkeyInner\nby switching the local 'str' variable to std::string_view over the\nexisting span, and update DecodeSecret / DecodeExtKey / DecodeExtPubKey\nto accept std::string_view directly (std::string and const char* callers\nare unaffected via implicit conversion).\n\nTo allow the string_view path all the way down, the internal base58\ndecoder is refactored from null-terminated const char* to a (psz, end)\npointer pair, replacing strlen() and *psz null checks with pointer\ncomparisons. The public DecodeBase58 / DecodeBase58Check APIs now take\nstd::string_view as well." }, { "sha": "ddcacd25e735dad4868bab7f618961a363f23239", "date": "2026-09-02T00:10:16Z", "message": "descriptor: replace O(n) INPUT_CHARSET.find() with precomputed lookup table\n\nReplace the O(n) linear INPUT_CHARSET.find() in DescriptorChecksum with\na precomputed 256-entry lookup table, reducing the checksum pass from\nO(95 * len) to O(len)." } ], "timeline": [ { "t": "2026-04-09T20:39:07Z", "kind": "comment", "who": "l0rinc", "assoc": "MEMBER", "text": "[quoted text omitted]\n\nThere have been a few base58 optimization attempts before (https://github.com/bitcoin/bitcoin/pull/29473 and independently before https://github.com/bitcoin/bitcoin/pull/21176) - would it help if we revived them?" }, { "t": "2026-04-10T12:08:59Z", "kind": "comment", "who": "brunoerg", "assoc": "MEMBER", "text": "[quoted text omitted]\n\nI'll take a look on those PRs and try, thank you. I think their focus is to improve/rewrites the algorithm itself, here is more about the way it's been used." }, { "t": "2026-06-07T13:53:30Z", "kind": "review_comment", "who": "sedited", "assoc": "MEMBER", "path": "src/script/descriptor.cpp", "commit": "2d86114c1b90d94593bda7f54f02b1403f678af2", "in_reply_to": null, "text": "Shouldn't really matter, but I thinks this could be constexpr too." }, { "t": "2026-06-07T14:04:32Z", "kind": "review", "who": "sedited", "assoc": "MEMBER", "state": "COMMENTED", "commit": "2d86114c1b90d94593bda7f54f02b1403f678af2", "text": "Concept ACK" }, { "t": "2026-06-10T15:50:16Z", "kind": "force_push", "who": "brunoerg", "commit": "0d8110a13579cee43b4d77bdbad943cc821cd6cb" }, { "t": "2026-06-10T15:52:00Z", "kind": "review_comment", "who": "brunoerg", "assoc": "MEMBER", "path": "src/script/descriptor.cpp", "commit": "2d86114c1b90d94593bda7f54f02b1403f678af2", "in_reply_to": 3369457038, "text": "Done." }, { "t": "2026-06-10T17:51:54Z", "kind": "force_push", "who": "brunoerg", "commit": "6dd023abbc9a1d8ece5dc9f9e186e7f5b1fb6f91" }, { "t": "2026-08-24T14:27:12Z", "kind": "force_push", "who": "brunoerg", "commit": "0339b33e41f13f87111c2e03e1ddc42bc6a596c4" }, { "t": "2026-08-25T09:02:24Z", "kind": "review_comment", "who": "hodlinator", "assoc": "MEMBER", "path": "src/key_io.cpp", "commit": "ddcacd25e735dad4868bab7f618961a363f23239", "in_reply_to": null, "text": "Started experimenting with returning `std::optional>` and validating `IsValid()` inside of the function but seems cleaner to leave that out of this PR. :)" }, { "t": "2026-08-25T09:49:17Z", "kind": "review_comment", "who": "hodlinator", "assoc": "MEMBER", "path": "src/base58.cpp", "commit": "0339b33e41f13f87111c2e03e1ddc42bc6a596c4", "in_reply_to": null, "text": "nit: Could document & enforce the `end` pointer not changing as well:\n```suggestion\n[[nodiscard]] static bool DecodeBase58(const char* psz, const char* const end, std::vector& vch, int max_ret_len)\n```" }, { "t": "2026-08-25T10:02:10Z", "kind": "review_comment", "who": "hodlinator", "assoc": "MEMBER", "path": "src/script/descriptor.cpp", "commit": "0339b33e41f13f87111c2e03e1ddc42bc6a596c4", "in_reply_to": null, "text": "nit-level suggestions:\n1. Omit `static` for `constexpr` variables as they are only evaluated once anyway (still needed for `INPUT_CHARSET` to simplify capture in lambda).\n2. Change element type of `INPUT_CHARSET_POS` to `int8_t` to better match range of possible values and decrease size.\n3. Omit cast to unsigned when indexing into `table` as at least GCC will trigger an assert at compile time when indexing out of bounds in `std::array`.\n4. Prefer `uint8_t` over longer `unsigned char`.\n```diff\n--- a/src/script/descriptor.cpp\n+++ b/src/script/descriptor.cpp\n@@ -143,23 +143,23 @@ std::string DescriptorChecksum(const std::span& span)\n \"ijklmnopqrstuvwxyzABCDEFGH`#\\\"\\\\ \";\n\n /** Lookup table mapping each ASCII byte to its position in INPUT_CHARSET, or -1 if not present. */\n- static constexpr std::array INPUT_CHARSET_POS = []() {\n- std::array table;\n+ constexpr std::array INPUT_CHARSET_POS = []() {\n+ std::array table;\n table.fill(-1);\n for (size_t i = 0; i < INPUT_CHARSET.size(); ++i) {\n- table[static_cast(INPUT_CHARSET[i])] = i;\n+ table[INPUT_CHARSET[i]] = i;\n }\n return table;\n }();\n\n /** The character set for the checksum itself (same as bech32). */\n- static constexpr std::string_view CHECKSUM_CHARSET = \"qpzry9x8gf2tvdw0s3jn54khce6mua7l\";\n+ constexpr std::string_view CHECKSUM_CHARSET = \"qpzry9x8gf2tvdw0s3jn54khce6mua7l\";\n\n uint64_t c = 1;\n int cls = 0;\n int clscount = 0;\n for (auto ch : span) {\n- auto pos = INPUT_CHARSET_POS[static_cast(ch)];\n+ int8_t pos = INPUT_CHARSET_POS[static_cast(ch)];\n if (pos == -1) return \"\";\n c = PolyMod(c, pos & 31); // Emit a symbol for the position inside the group, for every character.\n cls = cls * 3 + (pos >> 5); // Accumulate the group numbers\n```" }, { "t": "2026-08-25T12:10:31Z", "kind": "review", "who": "hodlinator", "assoc": "MEMBER", "state": "COMMENTED", "commit": "0339b33e41f13f87111c2e03e1ddc42bc6a596c4", "text": "ACK 0339b33e41f13f87111c2e03e1ddc42bc6a596c4\n\nWhy this change is acceptable when prior optimization attempts in this area were rejected (https://github.com/bitcoin/bitcoin/pull/35041#issuecomment-4217337173):\n* First commit is a *higher level* change to combine two calls to `DecodeBase58Check()` into one.\n* Second commit *trivially* replaces linear lookup with `O(1)` lookup table.\n\nIn my subjective view they have a lower impact on code readability than the rejected PRs. Also, the author of this PR motivates it through the concrete second-order effect of speeding up fuzz targets.\n\n(I'm still open to reviewing further optimizations in this area, without guarantees of priority).\n\nBenchmark code\n\n```diff\n--- a/src/bench/descriptors.cpp\n+++ b/src/bench/descriptors.cpp\n@@ -3,10 +3,12 @@\n // file COPYING or http://www.opensource.org/licenses/mit-license.php.\n\n #include \n+#include \n #include \n #include