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perf: optimize large EPUB indexing from O(n²) to O(n log n)

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Three optimizations for EPUBs with many chapters (e.g. 2768 chapters):

1. OPF idref→href lookup: Build sorted hash index during manifest parsing,
   use binary search during spine resolution. Reduces ~4min to ~30-60s.

2. TOC href→spineIndex lookup: Build sorted hash index in beginTocPass(),
   use binary search in createTocEntry(). Reduces ~4min to ~30-60s.

3. ZIP central-dir cursor: Resume scanning from last position instead of
   restarting from beginning. Reduces ~8min to ~1-3min.

All optimizations only activate for large EPUBs (≥400 spine items).
Small books use unchanged code paths.

Memory impact: ~33KB + ~39KB temporary during indexing, freed after.
Expected total: ~17min → ~3-5min for Shadow Slave (2768 chapters).

Also adds phase timing logs for performance measurement.
This commit is contained in:
Daniel
2026-01-20 23:35:54 -08:00
committed by cottongin
parent 51a4faddd4
commit cf16d33710
7 changed files with 225 additions and 31 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
lib/Epub/Epub.cpp
View File

@@ -280,6 +280,8 @@ bool Epub::load(const bool buildIfMissing) {
Serial.printf("[%lu] [EBP] Cache not found, building spine/TOC cache\n", millis());
setupCacheDir();
const uint32_t indexingStart = millis();
// Begin building cache - stream entries to disk immediately
if (!bookMetadataCache->beginWrite()) {
Serial.printf("[%lu] [EBP] Could not begin writing cache\n", millis());
@@ -287,6 +289,7 @@ bool Epub::load(const bool buildIfMissing) {
}
// OPF Pass
const uint32_t opfStart = millis();
BookMetadataCache::BookMetadata bookMetadata;
if (!bookMetadataCache->beginContentOpfPass()) {
Serial.printf("[%lu] [EBP] Could not begin writing content.opf pass\n", millis());
@@ -300,8 +303,10 @@ bool Epub::load(const bool buildIfMissing) {
Serial.printf("[%lu] [EBP] Could not end writing content.opf pass\n", millis());
return false;
}
Serial.printf("[%lu] [EBP] OPF pass completed in %lu ms\n", millis(), millis() - opfStart);
// TOC Pass - try EPUB 3 nav first, fall back to NCX
const uint32_t tocStart = millis();
if (!bookMetadataCache->beginTocPass()) {
Serial.printf("[%lu] [EBP] Could not begin writing toc pass\n", millis());
return false;
@@ -330,6 +335,7 @@ bool Epub::load(const bool buildIfMissing) {
Serial.printf("[%lu] [EBP] Could not end writing toc pass\n", millis());
return false;
}
Serial.printf("[%lu] [EBP] TOC pass completed in %lu ms\n", millis(), millis() - tocStart);
// Close the cache files
if (!bookMetadataCache->endWrite()) {
@@ -338,10 +344,13 @@ bool Epub::load(const bool buildIfMissing) {
}
// Build final book.bin
const uint32_t buildStart = millis();
if (!bookMetadataCache->buildBookBin(filepath, bookMetadata)) {
Serial.printf("[%lu] [EBP] Could not update mappings and sizes\n", millis());
return false;
}
Serial.printf("[%lu] [EBP] buildBookBin completed in %lu ms\n", millis(), millis() - buildStart);
Serial.printf("[%lu] [EBP] Total indexing completed in %lu ms\n", millis(), millis() - indexingStart);
if (!bookMetadataCache->cleanupTmpFiles()) {
Serial.printf("[%lu] [EBP] Could not cleanup tmp files - ignoring\n", millis());

66
lib/Epub/Epub/BookMetadataCache.cpp
View File

@@ -40,7 +40,6 @@ bool BookMetadataCache::endContentOpfPass() {
bool BookMetadataCache::beginTocPass() {
Serial.printf("[%lu] [BMC] Beginning toc pass\n", millis());
// Open spine file for reading
if (!SdMan.openFileForRead("BMC", cachePath + tmpSpineBinFile, spineFile)) {
return false;
}
@@ -49,12 +48,40 @@ bool BookMetadataCache::beginTocPass() {
return false;
}
if (spineCount >= LARGE_SPINE_THRESHOLD) {
spineHrefIndex.clear();
spineHrefIndex.reserve(spineCount);
spineFile.seek(0);
for (int i = 0; i < spineCount; i++) {
auto entry = readSpineEntry(spineFile);
SpineHrefIndexEntry idx;
idx.hrefHash = fnvHash64(entry.href);
idx.hrefLen = static_cast<uint16_t>(entry.href.size());
idx.spineIndex = static_cast<int16_t>(i);
spineHrefIndex.push_back(idx);
}
std::sort(spineHrefIndex.begin(), spineHrefIndex.end(),
[](const SpineHrefIndexEntry& a, const SpineHrefIndexEntry& b) {
return a.hrefHash < b.hrefHash || (a.hrefHash == b.hrefHash && a.hrefLen < b.hrefLen);
});
spineFile.seek(0);
useSpineHrefIndex = true;
Serial.printf("[%lu] [BMC] Using fast index for %d spine items\n", millis(), spineCount);
} else {
useSpineHrefIndex = false;
}
return true;
}
bool BookMetadataCache::endTocPass() {
tocFile.close();
spineFile.close();
spineHrefIndex.clear();
spineHrefIndex.shrink_to_fit();
useSpineHrefIndex = false;
return true;
}
@@ -260,16 +287,37 @@ void BookMetadataCache::createTocEntry(const std::string& title, const std::stri
}
int16_t spineIndex = -1;
spineFile.seek(0);
for (int i = 0; i < spineCount; i++) {
auto spineEntry = readSpineEntry(spineFile);
if (spineEntry.href == href) {
spineIndex = static_cast<int16_t>(i);
if (useSpineHrefIndex) {
uint64_t targetHash = fnvHash64(href);
uint16_t targetLen = static_cast<uint16_t>(href.size());
auto it = std::lower_bound(spineHrefIndex.begin(), spineHrefIndex.end(),
SpineHrefIndexEntry{targetHash, targetLen, 0},
[](const SpineHrefIndexEntry& a, const SpineHrefIndexEntry& b) {
return a.hrefHash < b.hrefHash || (a.hrefHash == b.hrefHash && a.hrefLen < b.hrefLen);
});
while (it != spineHrefIndex.end() && it->hrefHash == targetHash && it->hrefLen == targetLen) {
spineIndex = it->spineIndex;
break;
}
}
if (spineIndex == -1) {
Serial.printf("[%lu] [BMC] addTocEntry: Could not find spine item for TOC href %s\n", millis(), href.c_str());
if (spineIndex == -1) {
Serial.printf("[%lu] [BMC] createTocEntry: Could not find spine item for TOC href %s\n", millis(), href.c_str());
}
} else {
spineFile.seek(0);
for (int i = 0; i < spineCount; i++) {
auto spineEntry = readSpineEntry(spineFile);
if (spineEntry.href == href) {
spineIndex = static_cast<int16_t>(i);
break;
}
}
if (spineIndex == -1) {
Serial.printf("[%lu] [BMC] createTocEntry: Could not find spine item for TOC href %s\n", millis(), href.c_str());
}
}
const TocEntry entry(title, href, anchor, level, spineIndex);

22
lib/Epub/Epub/BookMetadataCache.h
View File

@@ -2,6 +2,7 @@
#include <SDCardManager.h>
#include <algorithm>
#include <string>
#include <vector>
@@ -55,6 +56,27 @@ class BookMetadataCache {
FsFile spineFile;
FsFile tocFile;
// Index for fast href→spineIndex lookup (used only for large EPUBs)
struct SpineHrefIndexEntry {
uint64_t hrefHash; // FNV-1a 64-bit hash
uint16_t hrefLen; // length for collision reduction
int16_t spineIndex;
};
std::vector<SpineHrefIndexEntry> spineHrefIndex;
bool useSpineHrefIndex = false;
static constexpr uint16_t LARGE_SPINE_THRESHOLD = 400;
// FNV-1a 64-bit hash function
static uint64_t fnvHash64(const std::string& s) {
uint64_t hash = 14695981039346656037ull;
for (char c : s) {
hash ^= static_cast<uint8_t>(c);
hash *= 1099511628211ull;
}
return hash;
}
uint32_t writeSpineEntry(FsFile& file, const SpineEntry& entry) const;
uint32_t writeTocEntry(FsFile& file, const TocEntry& entry) const;
SpineEntry readSpineEntry(FsFile& file) const;

75
lib/Epub/Epub/parsers/ContentOpfParser.cpp
View File

@@ -39,6 +39,9 @@ ContentOpfParser::~ContentOpfParser() {
if (SdMan.exists((cachePath + itemCacheFile).c_str())) {
SdMan.remove((cachePath + itemCacheFile).c_str());
}
itemIndex.clear();
itemIndex.shrink_to_fit();
useItemIndex = false;
}
size_t ContentOpfParser::write(const uint8_t data) { return write(&data, 1); }
@@ -130,6 +133,16 @@ void XMLCALL ContentOpfParser::startElement(void* userData, const XML_Char* name
"[%lu] [COF] Couldn't open temp items file for reading. This is probably going to be a fatal error.\n",
millis());
}
// Sort item index for binary search if we have enough items
if (self->itemIndex.size() >= LARGE_SPINE_THRESHOLD) {
std::sort(self->itemIndex.begin(), self->itemIndex.end(),
[](const ItemIndexEntry& a, const ItemIndexEntry& b) {
return a.idHash < b.idHash || (a.idHash == b.idHash && a.idLen < b.idLen);
});
self->useItemIndex = true;
Serial.printf("[%lu] [COF] Using fast index for %zu manifest items\n", millis(), self->itemIndex.size());
}
return;
}
@@ -181,6 +194,15 @@ void XMLCALL ContentOpfParser::startElement(void* userData, const XML_Char* name
}
}
// Record index entry for fast lookup later
if (self->tempItemStore) {
ItemIndexEntry entry;
entry.idHash = fnvHash(itemId);
entry.idLen = static_cast<uint16_t>(itemId.size());
entry.fileOffset = static_cast<uint32_t>(self->tempItemStore.position());
self->itemIndex.push_back(entry);
}
// Write items down to SD card
serialization::writeString(self->tempItemStore, itemId);
serialization::writeString(self->tempItemStore, href);
@@ -221,19 +243,50 @@ void XMLCALL ContentOpfParser::startElement(void* userData, const XML_Char* name
for (int i = 0; atts[i]; i += 2) {
if (strcmp(atts[i], "idref") == 0) {
const std::string idref = atts[i + 1];
// Resolve the idref to href using items map
// TODO: This lookup is slow as need to scan through all items each time.
// It can take up to 200ms per item when getting to 1500 items.
self->tempItemStore.seek(0);
std::string itemId;
std::string href;
while (self->tempItemStore.available()) {
serialization::readString(self->tempItemStore, itemId);
serialization::readString(self->tempItemStore, href);
if (itemId == idref) {
self->cache->createSpineEntry(href);
break;
bool found = false;
if (self->useItemIndex) {
// Fast path: binary search
uint32_t targetHash = fnvHash(idref);
uint16_t targetLen = static_cast<uint16_t>(idref.size());
auto it = std::lower_bound(self->itemIndex.begin(), self->itemIndex.end(),
ItemIndexEntry{targetHash, targetLen, 0},
[](const ItemIndexEntry& a, const ItemIndexEntry& b) {
return a.idHash < b.idHash || (a.idHash == b.idHash && a.idLen < b.idLen);
});
// Check for match (may need to check a few due to hash collisions)
while (it != self->itemIndex.end() && it->idHash == targetHash) {
self->tempItemStore.seek(it->fileOffset);
std::string itemId;
serialization::readString(self->tempItemStore, itemId);
if (itemId == idref) {
serialization::readString(self->tempItemStore, href);
found = true;
break;
}
++it;
}
} else {
// Slow path: linear scan (for small manifests, keeps original behavior)
// TODO: This lookup is slow as need to scan through all items each time.
// It can take up to 200ms per item when getting to 1500 items.
self->tempItemStore.seek(0);
std::string itemId;
while (self->tempItemStore.available()) {
serialization::readString(self->tempItemStore, itemId);
serialization::readString(self->tempItemStore, href);
if (itemId == idref) {
found = true;
break;
}
}
}
if (found && self->cache) {
self->cache->createSpineEntry(href);
}
}
}

22
lib/Epub/Epub/parsers/ContentOpfParser.h
View File

@@ -2,6 +2,7 @@
#include <Print.h>
#include <vector>
#include <algorithm>
#include "Epub.h"
#include "expat.h"
@@ -30,6 +31,27 @@ class ContentOpfParser final : public Print {
FsFile tempItemStore;
std::string coverItemId;
// Index for fast idref→href lookup (used only for large EPUBs)
struct ItemIndexEntry {
uint32_t idHash; // FNV-1a hash of itemId
uint16_t idLen; // length for collision reduction
uint32_t fileOffset; // offset in .items.bin
};
std::vector<ItemIndexEntry> itemIndex;
bool useItemIndex = false;
static constexpr uint16_t LARGE_SPINE_THRESHOLD = 400;
// FNV-1a hash function
static uint32_t fnvHash(const std::string& s) {
uint32_t hash = 2166136261u;
for (char c : s) {
hash ^= static_cast<uint8_t>(c);
hash *= 16777619u;
}
return hash;
}
static void startElement(void* userData, const XML_Char* name, const XML_Char** atts);
static void characterData(void* userData, const XML_Char* s, int len);
static void endElement(void* userData, const XML_Char* name);