internal static bool TryDecodeRational(MetadataEntry entry, out double value)
{
uint numerator;
uint denominator;
if (entry.Type != TagDataType.Rational || entry.LengthInBytes != 8)
{
value = 0.0;
return(false);
}
byte[] data = entry.GetDataReadOnly();
numerator = (uint)(data[0] | (data[1] << 8) | (data[2] << 16) | (data[3] << 24));
denominator = (uint)(data[4] | (data[5] << 8) | (data[6] << 16) | (data[7] << 24));
if (denominator == 0)
{
// Avoid division by zero.
value = 0.0;
return(false);
}
value = (double)numerator / denominator;
return(true);
}
internal static bool TryDecodeShort(MetadataEntry entry, out ushort value)
{
if (entry.Type != TagDataType.Short || entry.LengthInBytes != 2)
{
value = 0;
return(false);
}
byte[] data = entry.GetDataReadOnly();
value = (ushort)(data[0] | (data[1] << 8));
return(true);
}
private static IFDEntryInfo CreateIFDList(Dictionary <ushort, MetadataEntry> tags, long startOffset)
{
List <IFDEntry> ifdEntries = new List <IFDEntry>(tags.Count);
// Leave room for the tag count, tags and next IFD offset.
long ifdDataOffset = startOffset + sizeof(ushort) + ((long)tags.Count * IFDEntry.SizeOf) + sizeof(uint);
foreach (KeyValuePair <ushort, MetadataEntry> item in tags.OrderBy(i => i.Key))
{
MetadataEntry entry = item.Value;
uint count;
switch (entry.Type)
{
case TagDataType.Byte:
case TagDataType.Ascii:
case TagDataType.SByte:
case TagDataType.Undefined:
count = (uint)entry.LengthInBytes;
break;
case TagDataType.Short:
case TagDataType.SShort:
count = (uint)entry.LengthInBytes / 2;
break;
case TagDataType.Long:
case TagDataType.SLong:
case TagDataType.Float:
count = (uint)entry.LengthInBytes / 4;
break;
case TagDataType.Rational:
case TagDataType.SRational:
case TagDataType.Double:
count = (uint)entry.LengthInBytes / 8;
break;
default:
throw new InvalidOperationException("Unexpected tag type.");
}
if (TagDataTypeUtil.ValueFitsInOffsetField(entry.Type, count))
{
uint packedOffset = 0;
// Some applications may write EXIF fields with a count of zero.
// See https://github.com/0xC0000054/pdn-webp/issues/6.
if (count > 0)
{
byte[] data = entry.GetDataReadOnly();
// The data is always in little-endian byte order.
switch (data.Length)
{
case 1:
packedOffset |= data[0];
break;
case 2:
packedOffset |= data[0];
packedOffset |= (uint)data[1] << 8;
break;
case 3:
packedOffset |= data[0];
packedOffset |= (uint)data[1] << 8;
packedOffset |= (uint)data[2] << 16;
break;
case 4:
packedOffset |= data[0];
packedOffset |= (uint)data[1] << 8;
packedOffset |= (uint)data[2] << 16;
packedOffset |= (uint)data[3] << 24;
break;
default:
throw new InvalidOperationException("data.Length must be in the range of [1-4].");
}
}
ifdEntries.Add(new IFDEntry(entry.TagId, entry.Type, count, packedOffset));
}
else
{
ifdEntries.Add(new IFDEntry(entry.TagId, entry.Type, count, (uint)ifdDataOffset));
ifdDataOffset += entry.LengthInBytes;
// The IFD offsets must begin on a WORD boundary.
if ((ifdDataOffset & 1) == 1)
{
ifdDataOffset++;
}
}
}
return(new IFDEntryInfo(ifdEntries, startOffset, ifdDataOffset));
}
