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* Copyright (c) 2008, 2009, Google Inc. All rights reserved.
*
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* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
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* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "VDMXParser.h"
#include <stdlib.h>
#include <string.h>
#include "wtf/ByteOrder.h"
// Buffer helper class
//
// This class perform some trival buffer operations while checking for
// out-of-bounds errors. As a family they return false if anything is amiss,
// updating the current offset otherwise.
class Buffer {
public:
Buffer(const uint8_t* buffer, size_t length)
: m_buffer(buffer)
, m_length(length)
, m_offset(0) { }
bool skip(size_t numBytes)
{
if (m_offset + numBytes > m_length)
return false;
m_offset += numBytes;
return true;
}
bool readU8(uint8_t* value)
{
if (m_offset + sizeof(uint8_t) > m_length)
return false;
*value = m_buffer[m_offset];
m_offset += sizeof(uint8_t);
return true;
}
bool readU16(uint16_t* value)
{
if (m_offset + sizeof(uint16_t) > m_length)
return false;
memcpy(value, m_buffer + m_offset, sizeof(uint16_t));
*value = ntohs(*value);
m_offset += sizeof(uint16_t);
return true;
}
bool readS16(int16_t* value)
{
return readU16(reinterpret_cast<uint16_t*>(value));
}
size_t offset() const
{
return m_offset;
}
void setOffset(size_t newoffset)
{
m_offset = newoffset;
}
private:
const uint8_t *const m_buffer;
const size_t m_length;
size_t m_offset;
};
// VDMX parsing code.
//
// VDMX tables are found in some TrueType/OpenType fonts and contain
// ascender/descender overrides for certain (usually small) sizes. This is
// needed in order to match font metrics on Windows.
//
// Freetype does not parse these tables so we do so here.
namespace WebCore {
// Parse a TrueType VDMX table.
// yMax: (output) the ascender value from the table
// yMin: (output) the descender value from the table (negative!)
// vdmx: the table bytes
// vdmxLength: length of @vdmx, in bytes
// targetPixelSize: the pixel size of the font (e.g. 16)
//
// Returns true iff a suitable match are found. Otherwise, *yMax and *yMin are
// untouched. size_t must be 32-bits to avoid overflow.
//
// See http://www.microsoft.com/opentype/otspec/vdmx.htm
bool parseVDMX(int* yMax, int* yMin,
const uint8_t* vdmx, size_t vdmxLength,
unsigned targetPixelSize)
{
Buffer buf(vdmx, vdmxLength);
// We ignore the version. Future tables should be backwards compatible with
// this layout.
uint16_t numRatios;
if (!buf.skip(4) || !buf.readU16(&numRatios))
return false;
// Now we have two tables. Firstly we have @numRatios Ratio records, then a
// matching array of @numRatios offsets. We save the offset of the beginning
// of this second table.
//
// Range 6 <= x <= 262146
unsigned long offsetTableOffset =
buf.offset() + 4 /* sizeof struct ratio */ * numRatios;
unsigned desiredRatio = 0xffffffff;
// We read 4 bytes per record, so the offset range is
// 6 <= x <= 524286
for (unsigned i = 0; i < numRatios; ++i) {
uint8_t xRatio, yRatio1, yRatio2;
if (!buf.skip(1)
|| !buf.readU8(&xRatio)
|| !buf.readU8(&yRatio1)
|| !buf.readU8(&yRatio2))
return false;
// This either covers 1:1, or this is the default entry (0, 0, 0)
if ((xRatio == 1 && yRatio1 <= 1 && yRatio2 >= 1)
|| (xRatio == 0 && yRatio1 == 0 && yRatio2 == 0)) {
desiredRatio = i;
break;
}
}
if (desiredRatio == 0xffffffff) // no ratio found
return false;
// Range 10 <= x <= 393216
buf.setOffset(offsetTableOffset + sizeof(uint16_t) * desiredRatio);
// Now we read from the offset table to get the offset of another array
uint16_t groupOffset;
if (!buf.readU16(&groupOffset))
return false;
// Range 0 <= x <= 65535
buf.setOffset(groupOffset);
uint16_t numRecords;
if (!buf.readU16(&numRecords) || !buf.skip(sizeof(uint16_t)))
return false;
// We read 6 bytes per record, so the offset range is
// 4 <= x <= 458749
for (unsigned i = 0; i < numRecords; ++i) {
uint16_t pixelSize;
if (!buf.readU16(&pixelSize))
return false;
// the entries are sorted, so we can abort early if need be
if (pixelSize > targetPixelSize)
return false;
if (pixelSize == targetPixelSize) {
int16_t tempYMax, tempYMin;
if (!buf.readS16(&tempYMax)
|| !buf.readS16(&tempYMin))
return false;
*yMin = tempYMin;
*yMax = tempYMax;
return true;
}
if (!buf.skip(2 * sizeof(int16_t)))
return false;
}
return false;
}
} // namespace WebCore