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Bug 1412882 - Rework gfxFontUtils::MapCharToGlyphFormat4 to be more robust. r=lsalzman

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This commit is contained in:
Jonathan Kew 2018-05-19 08:32:22 +01:00
parent 94d0c55042
commit a482ff352e
3 changed files with 52 additions and 37 deletions
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79
gfx/thebes/gfxFontUtils.cpp
View File

@ -569,55 +569,64 @@ typedef struct {
#pragma pack()
uint32_t
gfxFontUtils::MapCharToGlyphFormat4(const uint8_t *aBuf, char16_t aCh)
gfxFontUtils::MapCharToGlyphFormat4(const uint8_t* aBuf, uint32_t aLength,
char16_t aCh)
{
const Format4Cmap *cmap4 = reinterpret_cast<const Format4Cmap*>(aBuf);
uint16_t segCount;
const AutoSwap_PRUint16 *endCodes;
const AutoSwap_PRUint16 *startCodes;
const AutoSwap_PRUint16 *idDelta;
const AutoSwap_PRUint16 *idRangeOffset;
uint16_t probe;
uint16_t rangeShiftOver2;
uint16_t index;
segCount = (uint16_t)(cmap4->segCountX2) / 2;
uint16_t segCount = (uint16_t)(cmap4->segCountX2) / 2;
endCodes = &cmap4->arrays[0];
startCodes = &cmap4->arrays[segCount + 1]; // +1 for reserved word between arrays
idDelta = &startCodes[segCount];
idRangeOffset = &idDelta[segCount];
const AutoSwap_PRUint16* endCodes = &cmap4->arrays[0];
const AutoSwap_PRUint16* startCodes = &cmap4->arrays[segCount + 1];
const AutoSwap_PRUint16* idDelta = &startCodes[segCount];
const AutoSwap_PRUint16* idRangeOffset = &idDelta[segCount];
probe = 1 << (uint16_t)(cmap4->entrySelector);
rangeShiftOver2 = (uint16_t)(cmap4->rangeShift) / 2;
if ((uint16_t)(startCodes[rangeShiftOver2]) <= aCh) {
index = rangeShiftOver2;
} else {
index = 0;
// Sanity-check that the fixed-size arrays don't exceed the buffer.
const uint8_t* const limit = aBuf + aLength;
if ((const uint8_t*)(&idRangeOffset[segCount]) > limit) {
return 0; // broken font, just bail out safely
}
while (probe > 1) {
probe >>= 1;
if ((uint16_t)(startCodes[index + probe]) <= aCh) {
index += probe;
// For most efficient binary search, we want to work on a range of segment
// indexes that is a power of 2 so that we can always halve it by shifting.
// So we find the largest power of 2 that is <= segCount.
// We will offset this range by segOffset so as to reach the end
// of the table, provided that doesn't put us beyond the target
// value from the outset.
uint32_t powerOf2 = mozilla::FindHighestBit(segCount);
uint32_t segOffset = segCount - powerOf2;
uint32_t idx = 0;
if (uint16_t(startCodes[segOffset]) <= aCh) {
idx = segOffset;
}
// Repeatedly halve the size of the range until we find the target group
while (powerOf2 > 1) {
powerOf2 >>= 1;
if (uint16_t(startCodes[idx + powerOf2]) <= aCh) {
idx += powerOf2;
}
}
if (aCh >= (uint16_t)(startCodes[index]) && aCh <= (uint16_t)(endCodes[index])) {
if (aCh >= uint16_t(startCodes[idx]) && aCh <= uint16_t(endCodes[idx])) {
uint16_t result;
if ((uint16_t)(idRangeOffset[index]) == 0) {
if (uint16_t(idRangeOffset[idx]) == 0) {
result = aCh;
} else {
uint16_t offset = aCh - (uint16_t)(startCodes[index]);
const AutoSwap_PRUint16 *glyphIndexTable =
(const AutoSwap_PRUint16*)((const char*)&idRangeOffset[index] +
(uint16_t)(idRangeOffset[index]));
uint16_t offset = aCh - uint16_t(startCodes[idx]);
const AutoSwap_PRUint16* glyphIndexTable =
(const AutoSwap_PRUint16*)((const char*)&idRangeOffset[idx] +
uint16_t(idRangeOffset[idx]));
if ((const uint8_t*)(glyphIndexTable + offset + 1) > limit) {
return 0; // broken font, just bail out safely
}
result = glyphIndexTable[offset];
}
// note that this is unsigned 16-bit arithmetic, and may wrap around
result += (uint16_t)(idDelta[index]);
// Note that this is unsigned 16-bit arithmetic, and may wrap around
// (which is required behavior per spec)
result += uint16_t(idDelta[idx]);
return result;
}
@ -761,7 +770,8 @@ gfxFontUtils::MapCharToGlyph(const uint8_t *aCmapBuf, uint32_t aBufLength,
switch (format) {
case 4:
gid = aUnicode < UNICODE_BMP_LIMIT ?
MapCharToGlyphFormat4(aCmapBuf + offset, char16_t(aUnicode)) : 0;
MapCharToGlyphFormat4(aCmapBuf + offset, aBufLength - offset,
char16_t(aUnicode)) : 0;
break;
case 10:
gid = MapCharToGlyphFormat10(aCmapBuf + offset, aUnicode);
@ -786,6 +796,7 @@ gfxFontUtils::MapCharToGlyph(const uint8_t *aCmapBuf, uint32_t aBufLength,
case 4:
if (aUnicode < UNICODE_BMP_LIMIT) {
varGID = MapCharToGlyphFormat4(aCmapBuf + offset,
aBufLength - offset,
char16_t(aUnicode));
}
break;

2
gfx/thebes/gfxFontUtils.h
View File

@ -804,7 +804,7 @@ public:
uint32_t& aUVSOffset);
static uint32_t
MapCharToGlyphFormat4(const uint8_t *aBuf, char16_t aCh);
MapCharToGlyphFormat4(const uint8_t *aBuf, uint32_t aLength, char16_t aCh);
static uint32_t
MapCharToGlyphFormat10(const uint8_t *aBuf, uint32_t aCh);

8
gfx/thebes/gfxHarfBuzzShaper.cpp
View File

@ -116,13 +116,15 @@ gfxHarfBuzzShaper::GetNominalGlyph(hb_codepoint_t unicode) const
NS_ASSERTION(mCmapTable && (mCmapFormat > 0) && (mSubtableOffset > 0),
"cmap data not correctly set up, expect disaster");
uint32_t length;
const uint8_t* data =
(const uint8_t*)hb_blob_get_data(mCmapTable, nullptr);
(const uint8_t*)hb_blob_get_data(mCmapTable, &length);
switch (mCmapFormat) {
case 4:
gid = unicode < UNICODE_BMP_LIMIT ?
gfxFontUtils::MapCharToGlyphFormat4(data + mSubtableOffset,
length - mSubtableOffset,
unicode) : 0;
break;
case 10:
@ -164,8 +166,9 @@ gfxHarfBuzzShaper::GetVariationGlyph(hb_codepoint_t unicode,
NS_ASSERTION(mCmapTable && (mCmapFormat > 0) && (mSubtableOffset > 0),
"cmap data not correctly set up, expect disaster");
uint32_t length;
const uint8_t* data =
(const uint8_t*)hb_blob_get_data(mCmapTable, nullptr);
(const uint8_t*)hb_blob_get_data(mCmapTable, &length);
if (mUVSTableOffset) {
hb_codepoint_t gid =
@ -183,6 +186,7 @@ gfxHarfBuzzShaper::GetVariationGlyph(hb_codepoint_t unicode,
case 4:
if (compat < UNICODE_BMP_LIMIT) {
return gfxFontUtils::MapCharToGlyphFormat4(data + mSubtableOffset,
length - mSubtableOffset,
compat);
}
break;