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compressor: use a prevector in compressed script serialization

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Use a prevector for stack allocation instead of heap allocation during
script compression and decompression. These functions were doing
millions of unnecessary heap allocations during IBD.

We introduce a CompressedScript type alias for this prevector. It is
size 33 as that is the maximum size of a compressed script.

Fix the DecompressScript header to match the variable name from
compressor.cpp

Signed-off-by: William Casarin <jb55@jb55.com>
This commit is contained in:
William Casarin
2020-05-01 17:31:38 -07:00
parent 844d2070a2
commit 83a425d25a
4 changed files with 27 additions and 13 deletions
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20
src/compressor.h
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@@ -6,14 +6,26 @@
#ifndef BITCOIN_COMPRESSOR_H
#define BITCOIN_COMPRESSOR_H
#include <prevector.h>
#include <primitives/transaction.h>
#include <script/script.h>
#include <serialize.h>
#include <span.h>
bool CompressScript(const CScript& script, std::vector<unsigned char> &out);
/**
* This saves us from making many heap allocations when serializing
* and deserializing compressed scripts.
*
* This prevector size is determined by the largest .resize() in the
* CompressScript function. The largest compressed script format is a
* compressed public key, which is 33 bytes.
*/
using CompressedScript = prevector<33, unsigned char>;
bool CompressScript(const CScript& script, CompressedScript& out);
unsigned int GetSpecialScriptSize(unsigned int nSize);
bool DecompressScript(CScript& script, unsigned int nSize, const std::vector<unsigned char> &out);
bool DecompressScript(CScript& script, unsigned int nSize, const CompressedScript& in);
/**
* Compress amount.
@@ -51,7 +63,7 @@ struct ScriptCompression
template<typename Stream>
void Ser(Stream &s, const CScript& script) {
std::vector<unsigned char> compr;
CompressedScript compr;
if (CompressScript(script, compr)) {
s << MakeSpan(compr);
return;
@@ -66,7 +78,7 @@ struct ScriptCompression
unsigned int nSize = 0;
s >> VARINT(nSize);
if (nSize < nSpecialScripts) {
std::vector<unsigned char> vch(GetSpecialScriptSize(nSize), 0x00);
CompressedScript vch(GetSpecialScriptSize(nSize), 0x00);
s >> MakeSpan(vch);
DecompressScript(script, nSize, vch);
return;