From 0d8f4fae3b97d285bd8bfd8da10498f66fbdbc77 Mon Sep 17 00:00:00 2001 From: "W. J. van der Laan" Date: Wed, 19 May 2021 10:07:25 +0200 Subject: [PATCH] Merge bitcoin/bitcoin#21173: util: faster HexStr => 13% faster blockToJSON 74bf850ac47735f2ef4306059d3e664d40cac85e faster HexStr => 13% faster blockToJSON (Martin Ankerl) Pull request description: `std::string`'s push_back is rather slow because it needs to check & update the string size. For `HexStr` the output string size is already easily know, so we can initially create the string with the correct size and then just assign the data. `HexStr` is heavily usd in `blockToJSON`, so this change is a noticeable benefit. Benchmark on an i7-8700 @3.2GHz: * 71,315,461.00 ns/op master * 62,842,490.00 ns/op this commit So this little change makes `blockToJSON` about ~13% faster. ACKs for top commit: laanwj: Code review ACK 74bf850ac47735f2ef4306059d3e664d40cac85e theStack: re-ACK 74bf850ac47735f2ef4306059d3e664d40cac85e Tree-SHA512: fc99105123edc11f4e40ed77aea80cf7f32e49c53369aa364b38395dcb48575e15040b0489ed30d0fe857c032a04e225c33e9d95cdfa109a3cb5a6ec9a972415 --- src/util/strencodings.cpp | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/src/util/strencodings.cpp b/src/util/strencodings.cpp index 5dda538e41..7e0969df8f 100644 --- a/src/util/strencodings.cpp +++ b/src/util/strencodings.cpp @@ -605,13 +605,14 @@ bool ParseHDKeypath(const std::string& keypath_str, std::vector& keypa std::string HexStr(const Span s) { - std::string rv; + std::string rv(s.size() * 2, '\0'); static constexpr char hexmap[16] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' }; - rv.reserve(s.size() * 2); - for (uint8_t v: s) { - rv.push_back(hexmap[v >> 4]); - rv.push_back(hexmap[v & 15]); + auto it = rv.begin(); + for (uint8_t v : s) { + *it++ = hexmap[v >> 4]; + *it++ = hexmap[v & 15]; } + assert(it == rv.end()); return rv; }