gecko-dev/gfx/thebes/gfxSkipChars.cpp

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8.4 KiB
C++

/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "gfxSkipChars.h"
#include <stdlib.h>
#include <algorithm>
#define SHORTCUT_FREQUENCY 256
// Even numbered list entries are "keep" entries
static bool
IsKeepEntry(uint32_t aEntry)
{
return !(aEntry & 1);
}
void
gfxSkipChars::BuildShortcuts()
{
if (!mList || mCharCount < SHORTCUT_FREQUENCY)
return;
mShortcuts = new Shortcut[mCharCount/SHORTCUT_FREQUENCY];
if (!mShortcuts)
return;
uint32_t i;
uint32_t nextShortcutIndex = 0;
uint32_t originalCharOffset = 0;
uint32_t skippedCharOffset = 0;
for (i = 0; i < mListLength; ++i) {
uint8_t len = mList[i];
// We use >= here to ensure that when mCharCount is a multiple of
// SHORTCUT_FREQUENCY, we fill in the final shortcut with a reference
// to the last element of mList. This means that in general when a list
// element ends on an offset that's a multiple of SHORTCUT_FREQUENCY,
// that list element is the shortcut for that offset, which is
// slightly suboptimal (the *next* element is the one we really want),
// but it's all correct and simpler this way.
while (originalCharOffset + len >= (nextShortcutIndex + 1)*SHORTCUT_FREQUENCY) {
mShortcuts[nextShortcutIndex] =
Shortcut(i, originalCharOffset, skippedCharOffset);
++nextShortcutIndex;
}
originalCharOffset += len;
if (IsKeepEntry(i)) {
skippedCharOffset += len;
}
}
}
void
gfxSkipCharsIterator::SetOffsets(uint32_t aOffset, bool aInOriginalString)
{
NS_ASSERTION(aOffset <= mSkipChars->mCharCount,
"Invalid offset");
if (mSkipChars->mListLength == 0) {
mOriginalStringOffset = mSkippedStringOffset = aOffset;
return;
}
if (aOffset == 0) {
// Start from the beginning of the string.
mSkippedStringOffset = 0;
mOriginalStringOffset = 0;
mListPrefixLength = 0;
mListPrefixKeepCharCount = 0;
mListPrefixCharCount = 0;
if (aInOriginalString) {
// Nothing more to do!
return;
}
}
if (aInOriginalString && mSkipChars->mShortcuts &&
abs(int32_t(aOffset) - int32_t(mListPrefixCharCount)) > SHORTCUT_FREQUENCY) {
// Take a shortcut. This makes SetOffsets(..., true) O(1) by bounding
// the iterations in the loop below to at most SHORTCUT_FREQUENCY iterations
uint32_t shortcutIndex = aOffset/SHORTCUT_FREQUENCY;
if (shortcutIndex == 0) {
mListPrefixLength = 0;
mListPrefixKeepCharCount = 0;
mListPrefixCharCount = 0;
} else {
const gfxSkipChars::Shortcut& shortcut = mSkipChars->mShortcuts[shortcutIndex - 1];
mListPrefixLength = shortcut.mListPrefixLength;
mListPrefixKeepCharCount = shortcut.mListPrefixKeepCharCount;
mListPrefixCharCount = shortcut.mListPrefixCharCount;
}
}
int32_t currentRunLength = mSkipChars->mList[mListPrefixLength];
for (;;) {
// See if aOffset is in the string segment described by
// mSkipChars->mList[mListPrefixLength]
uint32_t segmentOffset = aInOriginalString ? mListPrefixCharCount : mListPrefixKeepCharCount;
if ((aInOriginalString || IsKeepEntry(mListPrefixLength)) &&
aOffset >= segmentOffset && aOffset < segmentOffset + currentRunLength) {
int32_t offsetInSegment = aOffset - segmentOffset;
mOriginalStringOffset = mListPrefixCharCount + offsetInSegment;
mSkippedStringOffset = mListPrefixKeepCharCount;
if (IsKeepEntry(mListPrefixLength)) {
mSkippedStringOffset += offsetInSegment;
}
return;
}
if (aOffset < segmentOffset) {
// We need to move backwards
if (mListPrefixLength <= 0) {
// nowhere to go backwards
mOriginalStringOffset = mSkippedStringOffset = 0;
return;
}
// Go backwards one segment and restore invariants
--mListPrefixLength;
currentRunLength = mSkipChars->mList[mListPrefixLength];
mListPrefixCharCount -= currentRunLength;
if (IsKeepEntry(mListPrefixLength)) {
mListPrefixKeepCharCount -= currentRunLength;
}
} else {
// We need to move forwards
if (mListPrefixLength >= mSkipChars->mListLength - 1) {
// nowhere to go forwards
mOriginalStringOffset = mListPrefixCharCount + currentRunLength;
mSkippedStringOffset = mListPrefixKeepCharCount;
if (IsKeepEntry(mListPrefixLength)) {
mSkippedStringOffset += currentRunLength;
}
return;
}
// Go forwards one segment and restore invariants
mListPrefixCharCount += currentRunLength;
if (IsKeepEntry(mListPrefixLength)) {
mListPrefixKeepCharCount += currentRunLength;
}
++mListPrefixLength;
currentRunLength = mSkipChars->mList[mListPrefixLength];
}
}
}
bool
gfxSkipCharsIterator::IsOriginalCharSkipped(int32_t* aRunLength) const
{
if (mSkipChars->mListLength == 0) {
if (aRunLength) {
*aRunLength = mSkipChars->mCharCount - mOriginalStringOffset;
}
return mSkipChars->mCharCount == uint32_t(mOriginalStringOffset);
}
uint32_t listPrefixLength = mListPrefixLength;
// figure out which segment we're in
uint32_t currentRunLength = mSkipChars->mList[listPrefixLength];
// Zero-length list entries are possible. Advance until mListPrefixLength
// is pointing to a run with real characters (or we're at the end of the
// string).
while (currentRunLength == 0 && listPrefixLength < mSkipChars->mListLength - 1) {
++listPrefixLength;
// This does not break the iterator's invariant because no skipped
// or kept characters are being added
currentRunLength = mSkipChars->mList[listPrefixLength];
}
NS_ASSERTION(uint32_t(mOriginalStringOffset) >= mListPrefixCharCount,
"Invariant violation");
uint32_t offsetIntoCurrentRun =
uint32_t(mOriginalStringOffset) - mListPrefixCharCount;
if (listPrefixLength >= mSkipChars->mListLength - 1 &&
offsetIntoCurrentRun >= currentRunLength) {
NS_ASSERTION(listPrefixLength == mSkipChars->mListLength - 1 &&
offsetIntoCurrentRun == currentRunLength,
"Overran end of string");
// We're at the end of the string
if (aRunLength) {
*aRunLength = 0;
}
return true;
}
bool isSkipped = !IsKeepEntry(listPrefixLength);
if (aRunLength) {
// Long runs of all-skipped or all-kept characters will be encoded as
// sequences of 255, 0, 255, 0 etc. Compute the maximum run length by skipping
// over zero entries.
uint32_t runLength = currentRunLength - offsetIntoCurrentRun;
for (uint32_t i = listPrefixLength + 2; i < mSkipChars->mListLength; i += 2) {
if (mSkipChars->mList[i - 1] != 0)
break;
runLength += mSkipChars->mList[i];
}
*aRunLength = runLength;
}
return isSkipped;
}
void
gfxSkipCharsBuilder::FlushRun()
{
NS_ASSERTION((mBuffer.Length() & 1) == mRunSkipped,
"out of sync?");
// Fill in buffer entries starting at mBufferLength, as many as necessary
uint32_t charCount = mRunCharCount;
for (;;) {
uint32_t chars = std::min<uint32_t>(255, charCount);
if (!mBuffer.AppendElement(chars)) {
mInErrorState = true;
return;
}
charCount -= chars;
if (charCount == 0)
break;
if (!mBuffer.AppendElement(0)) {
mInErrorState = true;
return;
}
}
NS_ASSERTION(mCharCount + mRunCharCount >= mCharCount,
"String length overflow");
mCharCount += mRunCharCount;
mRunCharCount = 0;
mRunSkipped = !mRunSkipped;
}