descriptor: speed-up `Parse` (xpub/xpriv) in ~30% #35041

brunoerg commented at 6:19 PM on April 9, 2026: contributor

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):

Avoid redundant base58 decoding when parsing extended keys (this is the major improvement)

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.
Replace O(n) charset lookup with precomputed table

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.

Parse() with the following descriptor:

tr(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/*,xpub6DNEUJP1zLAZ1P6gYRba9FyxuppmkrPmSKz3FLM7msRwn2LEr4Ln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This PR:

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           90,253.50 |           11,079.90 |    0.2% |      0.01 | `ParseDescriptor`

Master:

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|          127,812.50 |            7,823.96 |    0.5% |      0.01 | `ParseDescriptor`

I didn't put the benchmark itself here but if reviewers think worth, I can do it.

Joint work with claude 😅

DrahtBot added the label Descriptors on Apr 9, 2026

brunoerg marked this as a draft on Apr 9, 2026

DrahtBot commented at 6:19 PM on April 9, 2026: contributor

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35041.

Reviews

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Concept ACK	sedited

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Possible places where named args for integral literals may be used (e.g. func(x, /*named_arg=*/0) in C++, and func(x, named_arg=0) in Python):

DecodeBase58Check(str, data, 78) in src/key_io.cpp

2026-06-10 17:52:05

brunoerg marked this as ready for review on Apr 9, 2026

l0rinc commented at 8:39 PM on April 9, 2026: contributor

Avoid redundant base58 decoding when parsing extended keys (this is the major improvement)

There have been a few base58 optimization attempts before (https://github.com/bitcoin/bitcoin/pull/29473 and independently before #21176) - would it help if we revived them?

brunoerg commented at 12:08 PM on April 10, 2026: contributor

Avoid redundant base58 decoding when parsing extended keys (this is the major improvement)

There have been a few base58 optimization attempts before (#29473 and independently before #21176) - would it help if we revived them?

I'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.

sedited requested review from hodlinator on Apr 20, 2026

in src/script/descriptor.cpp:127 in 2d86114c1b

 123 |          "0123456789()[],'/*abcdefgh@:$%{}"
 124 |          "IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~"
 125 |          "ijklmnopqrstuvwxyzABCDEFGH`#\"\\ ";
 126 |  
 127 | +    /** Lookup table mapping each ASCII byte to its position in INPUT_CHARSET, or -1 if not present. */
 128 | +    static const std::array<int, 256> INPUT_CHARSET_POS = []() {

sedited commented at 1:53 PM on June 7, 2026:

Shouldn't really matter, but I thinks this could be constexpr too.

brunoerg commented at 3:52 PM on June 10, 2026:

Done.

sedited commented at 2:04 PM on June 7, 2026: contributor

Concept ACK

descriptor, key_io: avoid redundant work when parsing keys

In ParsePubkeyInner, every extended key required two full base58
decodes: once via DecodeExtKey and again via DecodeExtPubKey, even
though at most one can succeed. Replace both calls with a new
DecodeExtKeyOrPubKey helper that performs a single DecodeBase58Check
and dispatches on the 4-byte version prefix to populate either the
xprv or xpub result.

Also eliminate the per-key std::string allocation in ParsePubkeyInner
by switching the local 'str' variable to std::string_view over the
existing span, and update DecodeSecret / DecodeExtKey / DecodeExtPubKey
to accept std::string_view directly (std::string and const char* callers
are unaffected via implicit conversion).

To allow the string_view path all the way down, the internal base58
decoder is refactored from null-terminated const char* to a (psz, end)
pointer pair, replacing strlen() and *psz null checks with pointer
comparisons. The public DecodeBase58 / DecodeBase58Check APIs now take
std::string_view as well.

d719bb8844

brunoerg force-pushed on Jun 10, 2026

DrahtBot added the label CI failed on Jun 10, 2026

DrahtBot commented at 5:18 PM on June 10, 2026: contributor

🚧 At least one of the CI tasks failed. Task iwyu: https://github.com/bitcoin/bitcoin/actions/runs/27288256306/job/80601410847 LLM reason (✨ experimental): CI failed because IWYU detected missing/incorrect includes in src/script/descriptor.cpp (autofix ran and then the IWYU check failed).

<details><summary>Hints</summary>

Try to run the tests locally, according to the documentation. However, a CI failure may still happen due to a number of reasons, for example:

Possibly due to a silent merge conflict (the changes in this pull request being incompatible with the current code in the target branch). If so, make sure to rebase on the latest commit of the target branch.
A sanitizer issue, which can only be found by compiling with the sanitizer and running the affected test.
An intermittent issue.

Leave a comment here, if you need help tracking down a confusing failure.

</details>

descriptor: replace O(n) INPUT_CHARSET.find() with precomputed lookup table

Replace the O(n) linear INPUT_CHARSET.find() in DescriptorChecksum with
a precomputed 256-entry lookup table, reducing the checksum pass from
O(95 * len) to O(len).

6dd023abbc

brunoerg force-pushed on Jun 10, 2026

DrahtBot removed the label CI failed on Jun 10, 2026