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llama : fix time complexity of string replacement (#9163)

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This change fixes a bug where replacing text in a very long string could
cause llama.cpp to hang indefinitely. This is because the algorithm used
was quadratic, due to memmove() when s.replace() is called in a loop. It
seems most search results and LLM responses actually provide the O(n**2)
algorithm, which is a great tragedy. Using a builder string fixes things
This commit is contained in:
Justine Tunney
2024-08-25 23:09:53 -07:00
committed by GitHub
parent 93bc3839f9
commit 436787f170
3 changed files with 30 additions and 12 deletions
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14
src/llama-impl.h
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@@ -31,11 +31,17 @@ void llama_log_callback_default(ggml_log_level level, const char * text, void *
static void replace_all(std::string & s, const std::string & search, const std::string & replace) {
if (search.empty()) {
return; // Avoid infinite loop if 'search' is an empty string
return;
}
std::string builder;
builder.reserve(s.length());
size_t pos = 0;
while ((pos = s.find(search, pos)) != std::string::npos) {
s.replace(pos, search.length(), replace);
pos += replace.length();
size_t last_pos = 0;
while ((pos = s.find(search, last_pos)) != std::string::npos) {
builder.append(s, last_pos, pos - last_pos);
builder.append(replace);
last_pos = pos + search.length();
}
builder.append(s, last_pos, std::string::npos);
s = std::move(builder);
}