ext/scintilla/src/PositionCache.cxx

   1 // Scintilla source code edit control
   2 /** @file PositionCache.cxx
   3  ** Classes for caching layout information.
   4  **/
   5 // Copyright 1998-2007 by Neil Hodgson <neilh@scintilla.org>
   6 // The License.txt file describes the conditions under which this software may be distributed.
   7
   8 #include <stdlib.h>
   9 #include <string.h>
  10 #include <stdio.h>
  11 #include <ctype.h>
  12
  13 #include <string>
  14 #include <vector>
  15 #include <map>
  16 #include <algorithm>
  17
  18 #include "Platform.h"
  19
  20 #include "ILexer.h"
  21 #include "Scintilla.h"
  22
  23 #include "SplitVector.h"
  24 #include "Partitioning.h"
  25 #include "RunStyles.h"
  26 #include "ContractionState.h"
  27 #include "CellBuffer.h"
  28 #include "KeyMap.h"
  29 #include "Indicator.h"
  30 #include "XPM.h"
  31 #include "LineMarker.h"
  32 #include "Style.h"
  33 #include "ViewStyle.h"
  34 #include "CharClassify.h"
  35 #include "Decoration.h"
  36 #include "CaseFolder.h"
  37 #include "Document.h"
  38 #include "UniConversion.h"
  39 #include "Selection.h"
  40 #include "PositionCache.h"
  41
  42 #ifdef SCI_NAMESPACE
  43 using namespace Scintilla;
  44 #endif
  45
  46 LineLayout::LineLayout(int maxLineLength_) :
  47         lineStarts(0),
  48         lenLineStarts(0),
  49         lineNumber(-1),
  50         inCache(false),
  51         maxLineLength(-1),
  52         numCharsInLine(0),
  53         numCharsBeforeEOL(0),
  54         validity(llInvalid),
  55         xHighlightGuide(0),
  56         highlightColumn(0),
  57         containsCaret(false),
  58         edgeColumn(0),
  59         chars(0),
  60         styles(0),
  61         positions(0),
  62         hotspot(0,0),
  63         widthLine(wrapWidthInfinite),
  64         lines(1),
  65         wrapIndent(0) {
  66         bracePreviousStyles[0] = 0;
  67         bracePreviousStyles[1] = 0;
  68         Resize(maxLineLength_);
  69 }
  70
  71 LineLayout::~LineLayout() {
  72         Free();
  73 }
  74
  75 void LineLayout::Resize(int maxLineLength_) {
  76         if (maxLineLength_ > maxLineLength) {
  77                 Free();
  78                 chars = new char[maxLineLength_ + 1];
  79                 styles = new unsigned char[maxLineLength_ + 1];
  80                 // Extra position allocated as sometimes the Windows
  81                 // GetTextExtentExPoint API writes an extra element.
  82                 positions = new XYPOSITION[maxLineLength_ + 1 + 1];
  83                 maxLineLength = maxLineLength_;
  84         }
  85 }
  86
  87 void LineLayout::Free() {
  88         delete []chars;
  89         chars = 0;
  90         delete []styles;
  91         styles = 0;
  92         delete []positions;
  93         positions = 0;
  94         delete []lineStarts;
  95         lineStarts = 0;
  96 }
  97
  98 void LineLayout::Invalidate(validLevel validity_) {
  99         if (validity > validity_)
 100                 validity = validity_;
 101 }
 102
 103 int LineLayout::LineStart(int line) const {
 104         if (line <= 0) {
 105                 return 0;
 106         } else if ((line >= lines) || !lineStarts) {
 107                 return numCharsInLine;
 108         } else {
 109                 return lineStarts[line];
 110         }
 111 }
 112
 113 int LineLayout::LineLastVisible(int line) const {
 114         if (line < 0) {
 115                 return 0;
 116         } else if ((line >= lines-1) || !lineStarts) {
 117                 return numCharsBeforeEOL;
 118         } else {
 119                 return lineStarts[line+1];
 120         }
 121 }
 122
 123 Range LineLayout::SubLineRange(int subLine) const {
 124         return Range(LineStart(subLine), LineLastVisible(subLine));
 125 }
 126
 127 bool LineLayout::InLine(int offset, int line) const {
 128         return ((offset >= LineStart(line)) && (offset < LineStart(line + 1))) ||
 129                 ((offset == numCharsInLine) && (line == (lines-1)));
 130 }
 131
 132 void LineLayout::SetLineStart(int line, int start) {
 133         if ((line >= lenLineStarts) && (line != 0)) {
 134                 int newMaxLines = line + 20;
 135                 int *newLineStarts = new int[newMaxLines];
 136                 for (int i = 0; i < newMaxLines; i++) {
 137                         if (i < lenLineStarts)
 138                                 newLineStarts[i] = lineStarts[i];
 139                         else
 140                                 newLineStarts[i] = 0;
 141                 }
 142                 delete []lineStarts;
 143                 lineStarts = newLineStarts;
 144                 lenLineStarts = newMaxLines;
 145         }
 146         lineStarts[line] = start;
 147 }
 148
 149 void LineLayout::SetBracesHighlight(Range rangeLine, const Position braces[],
 150                                     char bracesMatchStyle, int xHighlight, bool ignoreStyle) {
 151         if (!ignoreStyle && rangeLine.ContainsCharacter(braces[0])) {
 152                 int braceOffset = braces[0] - rangeLine.start;
 153                 if (braceOffset < numCharsInLine) {
 154                         bracePreviousStyles[0] = styles[braceOffset];
 155                         styles[braceOffset] = bracesMatchStyle;
 156                 }
 157         }
 158         if (!ignoreStyle && rangeLine.ContainsCharacter(braces[1])) {
 159                 int braceOffset = braces[1] - rangeLine.start;
 160                 if (braceOffset < numCharsInLine) {
 161                         bracePreviousStyles[1] = styles[braceOffset];
 162                         styles[braceOffset] = bracesMatchStyle;
 163                 }
 164         }
 165         if ((braces[0] >= rangeLine.start && braces[1] <= rangeLine.end) ||
 166                 (braces[1] >= rangeLine.start && braces[0] <= rangeLine.end)) {
 167                 xHighlightGuide = xHighlight;
 168         }
 169 }
 170
 171 void LineLayout::RestoreBracesHighlight(Range rangeLine, const Position braces[], bool ignoreStyle) {
 172         if (!ignoreStyle && rangeLine.ContainsCharacter(braces[0])) {
 173                 int braceOffset = braces[0] - rangeLine.start;
 174                 if (braceOffset < numCharsInLine) {
 175                         styles[braceOffset] = bracePreviousStyles[0];
 176                 }
 177         }
 178         if (!ignoreStyle && rangeLine.ContainsCharacter(braces[1])) {
 179                 int braceOffset = braces[1] - rangeLine.start;
 180                 if (braceOffset < numCharsInLine) {
 181                         styles[braceOffset] = bracePreviousStyles[1];
 182                 }
 183         }
 184         xHighlightGuide = 0;
 185 }
 186
 187 int LineLayout::FindBefore(XYPOSITION x, int lower, int upper) const {
 188         do {
 189                 int middle = (upper + lower + 1) / 2;   // Round high
 190                 XYPOSITION posMiddle = positions[middle];
 191                 if (x < posMiddle) {
 192                         upper = middle - 1;
 193                 } else {
 194                         lower = middle;
 195                 }
 196         } while (lower < upper);
 197         return lower;
 198 }
 199
 200
 201 int LineLayout::FindPositionFromX(XYPOSITION x, Range range, bool charPosition) const {
 202         int pos = FindBefore(x, range.start, range.end);
 203         while (pos < range.end) {
 204                 if (charPosition) {
 205                         if (x < (positions[pos + 1])) {
 206                                 return pos;
 207                         }
 208                 } else {
 209                         if (x < ((positions[pos] + positions[pos + 1]) / 2)) {
 210                                 return pos;
 211                         }
 212                 }
 213                 pos++;
 214         }
 215         return range.end;
 216 }
 217
 218 Point LineLayout::PointFromPosition(int posInLine, int lineHeight) const {
 219         Point pt;
 220         // In case of very long line put x at arbitrary large position
 221         if (posInLine > maxLineLength) {
 222                 pt.x = positions[maxLineLength] - positions[LineStart(lines)];
 223         }
 224
 225         for (int subLine = 0; subLine < lines; subLine++) {
 226                 const Range rangeSubLine = SubLineRange(subLine);
 227                 if (posInLine >= rangeSubLine.start) {
 228                         pt.y = static_cast<XYPOSITION>(subLine*lineHeight);
 229                         if (posInLine <= rangeSubLine.end) {
 230                                 pt.x = positions[posInLine] - positions[rangeSubLine.start];
 231                                 if (rangeSubLine.start != 0)    // Wrapped lines may be indented
 232                                         pt.x += wrapIndent;
 233                         }
 234                 } else {
 235                         break;
 236                 }
 237         }
 238         return pt;
 239 }
 240
 241 int LineLayout::EndLineStyle() const {
 242         return styles[numCharsBeforeEOL > 0 ? numCharsBeforeEOL-1 : 0];
 243 }
 244
 245 LineLayoutCache::LineLayoutCache() :
 246         level(0),
 247         allInvalidated(false), styleClock(-1), useCount(0) {
 248         Allocate(0);
 249 }
 250
 251 LineLayoutCache::~LineLayoutCache() {
 252         Deallocate();
 253 }
 254
 255 void LineLayoutCache::Allocate(size_t length_) {
 256         PLATFORM_ASSERT(cache.empty());
 257         allInvalidated = false;
 258         cache.resize(length_);
 259 }
 260
 261 void LineLayoutCache::AllocateForLevel(int linesOnScreen, int linesInDoc) {
 262         PLATFORM_ASSERT(useCount == 0);
 263         size_t lengthForLevel = 0;
 264         if (level == llcCaret) {
 265                 lengthForLevel = 1;
 266         } else if (level == llcPage) {
 267                 lengthForLevel = linesOnScreen + 1;
 268         } else if (level == llcDocument) {
 269                 lengthForLevel = linesInDoc;
 270         }
 271         if (lengthForLevel > cache.size()) {
 272                 Deallocate();
 273                 Allocate(lengthForLevel);
 274         } else {
 275                 if (lengthForLevel < cache.size()) {
 276                         for (size_t i = lengthForLevel; i < cache.size(); i++) {
 277                                 delete cache[i];
 278                                 cache[i] = 0;
 279                         }
 280                 }
 281                 cache.resize(lengthForLevel);
 282         }
 283         PLATFORM_ASSERT(cache.size() == lengthForLevel);
 284 }
 285
 286 void LineLayoutCache::Deallocate() {
 287         PLATFORM_ASSERT(useCount == 0);
 288         for (size_t i = 0; i < cache.size(); i++)
 289                 delete cache[i];
 290         cache.clear();
 291 }
 292
 293 void LineLayoutCache::Invalidate(LineLayout::validLevel validity_) {
 294         if (!cache.empty() && !allInvalidated) {
 295                 for (size_t i = 0; i < cache.size(); i++) {
 296                         if (cache[i]) {
 297                                 cache[i]->Invalidate(validity_);
 298                         }
 299                 }
 300                 if (validity_ == LineLayout::llInvalid) {
 301                         allInvalidated = true;
 302                 }
 303         }
 304 }
 305
 306 void LineLayoutCache::SetLevel(int level_) {
 307         allInvalidated = false;
 308         if ((level_ != -1) && (level != level_)) {
 309                 level = level_;
 310                 Deallocate();
 311         }
 312 }
 313
 314 LineLayout *LineLayoutCache::Retrieve(int lineNumber, int lineCaret, int maxChars, int styleClock_,
 315                                       int linesOnScreen, int linesInDoc) {
 316         AllocateForLevel(linesOnScreen, linesInDoc);
 317         if (styleClock != styleClock_) {
 318                 Invalidate(LineLayout::llCheckTextAndStyle);
 319                 styleClock = styleClock_;
 320         }
 321         allInvalidated = false;
 322         int pos = -1;
 323         LineLayout *ret = 0;
 324         if (level == llcCaret) {
 325                 pos = 0;
 326         } else if (level == llcPage) {
 327                 if (lineNumber == lineCaret) {
 328                         pos = 0;
 329                 } else if (cache.size() > 1) {
 330                         pos = 1 + (lineNumber % (cache.size() - 1));
 331                 }
 332         } else if (level == llcDocument) {
 333                 pos = lineNumber;
 334         }
 335         if (pos >= 0) {
 336                 PLATFORM_ASSERT(useCount == 0);
 337                 if (!cache.empty() && (pos < static_cast<int>(cache.size()))) {
 338                         if (cache[pos]) {
 339                                 if ((cache[pos]->lineNumber != lineNumber) ||
 340                                         (cache[pos]->maxLineLength < maxChars)) {
 341                                         delete cache[pos];
 342                                         cache[pos] = 0;
 343                                 }
 344                         }
 345                         if (!cache[pos]) {
 346                                 cache[pos] = new LineLayout(maxChars);
 347                         }
 348                         cache[pos]->lineNumber = lineNumber;
 349                         cache[pos]->inCache = true;
 350                         ret = cache[pos];
 351                         useCount++;
 352                 }
 353         }
 354
 355         if (!ret) {
 356                 ret = new LineLayout(maxChars);
 357                 ret->lineNumber = lineNumber;
 358         }
 359
 360         return ret;
 361 }
 362
 363 void LineLayoutCache::Dispose(LineLayout *ll) {
 364         allInvalidated = false;
 365         if (ll) {
 366                 if (!ll->inCache) {
 367                         delete ll;
 368                 } else {
 369                         useCount--;
 370                 }
 371         }
 372 }
 373
 374 // Simply pack the (maximum 4) character bytes into an int
 375 static inline int KeyFromString(const char *charBytes, size_t len) {
 376         PLATFORM_ASSERT(len <= 4);
 377         int k=0;
 378         for (size_t i=0; i<len && charBytes[i]; i++) {
 379                 k = k * 0x100;
 380                 k += static_cast<unsigned char>(charBytes[i]);
 381         }
 382         return k;
 383 }
 384
 385 SpecialRepresentations::SpecialRepresentations() {
 386         std::fill(startByteHasReprs, startByteHasReprs+0x100, 0);
 387 }
 388
 389 void SpecialRepresentations::SetRepresentation(const char *charBytes, const char *value) {
 390         MapRepresentation::iterator it = mapReprs.find(KeyFromString(charBytes, UTF8MaxBytes));
 391         if (it == mapReprs.end()) {
 392                 // New entry so increment for first byte
 393                 startByteHasReprs[static_cast<unsigned char>(charBytes[0])]++;
 394         }
 395         mapReprs[KeyFromString(charBytes, UTF8MaxBytes)] = Representation(value);
 396 }
 397
 398 void SpecialRepresentations::ClearRepresentation(const char *charBytes) {
 399         MapRepresentation::iterator it = mapReprs.find(KeyFromString(charBytes, UTF8MaxBytes));
 400         if (it != mapReprs.end()) {
 401                 mapReprs.erase(it);
 402                 startByteHasReprs[static_cast<unsigned char>(charBytes[0])]--;
 403         }
 404 }
 405
 406 const Representation *SpecialRepresentations::RepresentationFromCharacter(const char *charBytes, size_t len) const {
 407         PLATFORM_ASSERT(len <= 4);
 408         if (!startByteHasReprs[static_cast<unsigned char>(charBytes[0])])
 409                 return 0;
 410         MapRepresentation::const_iterator it = mapReprs.find(KeyFromString(charBytes, len));
 411         if (it != mapReprs.end()) {
 412                 return &(it->second);
 413         }
 414         return 0;
 415 }
 416
 417 bool SpecialRepresentations::Contains(const char *charBytes, size_t len) const {
 418         PLATFORM_ASSERT(len <= 4);
 419         if (!startByteHasReprs[static_cast<unsigned char>(charBytes[0])])
 420                 return false;
 421         MapRepresentation::const_iterator it = mapReprs.find(KeyFromString(charBytes, len));
 422         return it != mapReprs.end();
 423 }
 424
 425 void SpecialRepresentations::Clear() {
 426         mapReprs.clear();
 427         std::fill(startByteHasReprs, startByteHasReprs+0x100, 0);
 428 }
 429
 430 void BreakFinder::Insert(int val) {
 431         if (val > nextBreak) {
 432                 const std::vector<int>::iterator it = std::lower_bound(selAndEdge.begin(), selAndEdge.end(), val);
 433                 if (it == selAndEdge.end()) {
 434                         selAndEdge.push_back(val);
 435                 } else if (*it != val) {
 436                         selAndEdge.insert(it, 1, val);
 437                 }
 438         }
 439 }
 440
 441 BreakFinder::BreakFinder(const LineLayout *ll_, const Selection *psel, int lineStart_, int lineEnd_, int posLineStart_,
 442         int xStart, bool breakForSelection, const Document *pdoc_, const SpecialRepresentations *preprs_) :
 443         ll(ll_),
 444         lineStart(lineStart_),
 445         lineEnd(lineEnd_),
 446         posLineStart(posLineStart_),
 447         nextBreak(lineStart_),
 448         saeCurrentPos(0),
 449         saeNext(0),
 450         subBreak(-1),
 451         pdoc(pdoc_),
 452         encodingFamily(pdoc_->CodePageFamily()),
 453         preprs(preprs_) {
 454
 455         // Search for first visible break
 456         // First find the first visible character
 457         if (xStart > 0.0f)
 458                 nextBreak = ll->FindBefore(static_cast<XYPOSITION>(xStart), lineStart, lineEnd);
 459         // Now back to a style break
 460         while ((nextBreak > lineStart) && (ll->styles[nextBreak] == ll->styles[nextBreak - 1])) {
 461                 nextBreak--;
 462         }
 463
 464         if (breakForSelection) {
 465                 SelectionPosition posStart(posLineStart);
 466                 SelectionPosition posEnd(posLineStart + lineEnd);
 467                 SelectionSegment segmentLine(posStart, posEnd);
 468                 for (size_t r=0; r<psel->Count(); r++) {
 469                         SelectionSegment portion = psel->Range(r).Intersect(segmentLine);
 470                         if (!(portion.start == portion.end)) {
 471                                 if (portion.start.IsValid())
 472                                         Insert(portion.start.Position() - posLineStart);
 473                                 if (portion.end.IsValid())
 474                                         Insert(portion.end.Position() - posLineStart);
 475                         }
 476                 }
 477         }
 478
 479         Insert(ll->edgeColumn);
 480         Insert(lineEnd);
 481         saeNext = (!selAndEdge.empty()) ? selAndEdge[0] : -1;
 482 }
 483
 484 BreakFinder::~BreakFinder() {
 485 }
 486
 487 TextSegment BreakFinder::Next() {
 488         if (subBreak == -1) {
 489                 int prev = nextBreak;
 490                 while (nextBreak < lineEnd) {
 491                         int charWidth = 1;
 492                         if (encodingFamily == efUnicode)
 493                                 charWidth = UTF8DrawBytes(reinterpret_cast<unsigned char *>(ll->chars) + nextBreak, lineEnd - nextBreak);
 494                         else if (encodingFamily == efDBCS)
 495                                 charWidth = pdoc->IsDBCSLeadByte(ll->chars[nextBreak]) ? 2 : 1;
 496                         const Representation *repr = preprs->RepresentationFromCharacter(ll->chars + nextBreak, charWidth);
 497                         if (((nextBreak > 0) && (ll->styles[nextBreak] != ll->styles[nextBreak - 1])) ||
 498                                         repr ||
 499                                         (nextBreak == saeNext)) {
 500                                 while ((nextBreak >= saeNext) && (saeNext < lineEnd)) {
 501                                         saeCurrentPos++;
 502                                         saeNext = (saeCurrentPos < selAndEdge.size()) ? selAndEdge[saeCurrentPos] : lineEnd;
 503                                 }
 504                                 if ((nextBreak > prev) || repr) {
 505                                         // Have a segment to report
 506                                         if (nextBreak == prev) {
 507                                                 nextBreak += charWidth;
 508                                         } else {
 509                                                 repr = 0;       // Optimize -> should remember repr
 510                                         }
 511                                         if ((nextBreak - prev) < lengthStartSubdivision) {
 512                                                 return TextSegment(prev, nextBreak - prev, repr);
 513                                         } else {
 514                                                 break;
 515                                         }
 516                                 }
 517                         }
 518                         nextBreak += charWidth;
 519                 }
 520                 if ((nextBreak - prev) < lengthStartSubdivision) {
 521                         return TextSegment(prev, nextBreak - prev);
 522                 }
 523                 subBreak = prev;
 524         }
 525         // Splitting up a long run from prev to nextBreak in lots of approximately lengthEachSubdivision.
 526         // For very long runs add extra breaks after spaces or if no spaces before low punctuation.
 527         int startSegment = subBreak;
 528         if ((nextBreak - subBreak) <= lengthEachSubdivision) {
 529                 subBreak = -1;
 530                 return TextSegment(startSegment, nextBreak - startSegment);
 531         } else {
 532                 subBreak += pdoc->SafeSegment(ll->chars + subBreak, nextBreak-subBreak, lengthEachSubdivision);
 533                 if (subBreak >= nextBreak) {
 534                         subBreak = -1;
 535                         return TextSegment(startSegment, nextBreak - startSegment);
 536                 } else {
 537                         return TextSegment(startSegment, subBreak - startSegment);
 538                 }
 539         }
 540 }
 541
 542 bool BreakFinder::More() const {
 543         return (subBreak >= 0) || (nextBreak < lineEnd);
 544 }
 545
 546 PositionCacheEntry::PositionCacheEntry() :
 547         styleNumber(0), len(0), clock(0), positions(0) {
 548 }
 549
 550 void PositionCacheEntry::Set(unsigned int styleNumber_, const char *s_,
 551         unsigned int len_, XYPOSITION *positions_, unsigned int clock_) {
 552         Clear();
 553         styleNumber = styleNumber_;
 554         len = len_;
 555         clock = clock_;
 556         if (s_ && positions_) {
 557                 positions = new XYPOSITION[len + (len / 4) + 1];
 558                 for (unsigned int i=0; i<len; i++) {
 559                         positions[i] = positions_[i];
 560                 }
 561                 memcpy(reinterpret_cast<char *>(reinterpret_cast<void *>(positions + len)), s_, len);
 562         }
 563 }
 564
 565 PositionCacheEntry::~PositionCacheEntry() {
 566         Clear();
 567 }
 568
 569 void PositionCacheEntry::Clear() {
 570         delete []positions;
 571         positions = 0;
 572         styleNumber = 0;
 573         len = 0;
 574         clock = 0;
 575 }
 576
 577 bool PositionCacheEntry::Retrieve(unsigned int styleNumber_, const char *s_,
 578         unsigned int len_, XYPOSITION *positions_) const {
 579         if ((styleNumber == styleNumber_) && (len == len_) &&
 580                 (memcmp(reinterpret_cast<char *>(reinterpret_cast<void *>(positions + len)), s_, len)== 0)) {
 581                 for (unsigned int i=0; i<len; i++) {
 582                         positions_[i] = positions[i];
 583                 }
 584                 return true;
 585         } else {
 586                 return false;
 587         }
 588 }
 589
 590 unsigned int PositionCacheEntry::Hash(unsigned int styleNumber_, const char *s, unsigned int len_) {
 591         unsigned int ret = s[0] << 7;
 592         for (unsigned int i=0; i<len_; i++) {
 593                 ret *= 1000003;
 594                 ret ^= s[i];
 595         }
 596         ret *= 1000003;
 597         ret ^= len_;
 598         ret *= 1000003;
 599         ret ^= styleNumber_;
 600         return ret;
 601 }
 602
 603 bool PositionCacheEntry::NewerThan(const PositionCacheEntry &other) const {
 604         return clock > other.clock;
 605 }
 606
 607 void PositionCacheEntry::ResetClock() {
 608         if (clock > 0) {
 609                 clock = 1;
 610         }
 611 }
 612
 613 PositionCache::PositionCache() {
 614         clock = 1;
 615         pces.resize(0x400);
 616         allClear = true;
 617 }
 618
 619 PositionCache::~PositionCache() {
 620         Clear();
 621 }
 622
 623 void PositionCache::Clear() {
 624         if (!allClear) {
 625                 for (size_t i=0; i<pces.size(); i++) {
 626                         pces[i].Clear();
 627                 }
 628         }
 629         clock = 1;
 630         allClear = true;
 631 }
 632
 633 void PositionCache::SetSize(size_t size_) {
 634         Clear();
 635         pces.resize(size_);
 636 }
 637
 638 void PositionCache::MeasureWidths(Surface *surface, const ViewStyle &vstyle, unsigned int styleNumber,
 639         const char *s, unsigned int len, XYPOSITION *positions, Document *pdoc) {
 640
 641         allClear = false;
 642         size_t probe = pces.size();     // Out of bounds
 643         if ((!pces.empty()) && (len < 30)) {
 644                 // Only store short strings in the cache so it doesn't churn with
 645                 // long comments with only a single comment.
 646
 647                 // Two way associative: try two probe positions.
 648                 unsigned int hashValue = PositionCacheEntry::Hash(styleNumber, s, len);
 649                 probe = hashValue % pces.size();
 650                 if (pces[probe].Retrieve(styleNumber, s, len, positions)) {
 651                         return;
 652                 }
 653                 unsigned int probe2 = (hashValue * 37) % pces.size();
 654                 if (pces[probe2].Retrieve(styleNumber, s, len, positions)) {
 655                         return;
 656                 }
 657                 // Not found. Choose the oldest of the two slots to replace
 658                 if (pces[probe].NewerThan(pces[probe2])) {
 659                         probe = probe2;
 660                 }
 661         }
 662         if (len > BreakFinder::lengthStartSubdivision) {
 663                 // Break up into segments
 664                 unsigned int startSegment = 0;
 665                 XYPOSITION xStartSegment = 0;
 666                 while (startSegment < len) {
 667                         unsigned int lenSegment = pdoc->SafeSegment(s + startSegment, len - startSegment, BreakFinder::lengthEachSubdivision);
 668                         FontAlias fontStyle = vstyle.styles[styleNumber].font;
 669                         surface->MeasureWidths(fontStyle, s + startSegment, lenSegment, positions + startSegment);
 670                         for (unsigned int inSeg = 0; inSeg < lenSegment; inSeg++) {
 671                                 positions[startSegment + inSeg] += xStartSegment;
 672                         }
 673                         xStartSegment = positions[startSegment + lenSegment - 1];
 674                         startSegment += lenSegment;
 675                 }
 676         } else {
 677                 FontAlias fontStyle = vstyle.styles[styleNumber].font;
 678                 surface->MeasureWidths(fontStyle, s, len, positions);
 679         }
 680         if (probe < pces.size()) {
 681                 // Store into cache
 682                 clock++;
 683                 if (clock > 60000) {
 684                         // Since there are only 16 bits for the clock, wrap it round and
 685                         // reset all cache entries so none get stuck with a high clock.
 686                         for (size_t i=0; i<pces.size(); i++) {
 687                                 pces[i].ResetClock();
 688                         }
 689                         clock = 2;
 690                 }
 691                 pces[probe].Set(styleNumber, s, len, positions, clock);
 692         }
 693 }