As of version 5.0, Xceed Zip supports the Zip64
zip file format which means that 64-bit values need to be handled and displayed properly. In order to keep Xceed Zip backwards compatible with previous versions, some the events that provide byte/size information, as well as the GetZipFileInformation method were given a 64-bit counterpart. These counterparts have the same names as the regular events except that they have "64" added to the name (e.g., GlobalStatus64)
Each of these counterparts has 2 parameters related to byte/size rather than one. For example, if the 32-bit version of an event had a parameter named lSize, in the 64-bit version of the event, this parameter would be split in two: lSizeLow and lSizeHigh. lSize low represents the 32 low-order bits and lSizeHigh represents the 32 high-order bits. These values can then be combined to retrieve the complete 64-bit value.
To split zip files into parts that are larger than 4 gigs, the SplitSize property must be used in conjunction with the SplitSizeHigh property, or the SplitSize64 property, which is the 64-bit counterpart of the SplitSize and SplitSizeHigh properties, can be used.
For example, if we were to take the hexadecimal value 0xFFFFFFFE and separate it into its low-order and high-order bits, the low-order bits would be FFFE and the high-order bits would be FFFF.
These values can then be combined in order to retrieve the 64-bit value as demonstrated in the following Visual Basic example:
| Visual Basic |
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Private Function GetDoubleFromTwoLongs( ByVal lHigh As Long, ByVal lLow As Long ) As Double
Dim returnValue As Double
' Since VB's longs are signed, we need to bring them back
' to a positive value before combining them, if applicable
returnValue = IIf( lHigh < 0, 4294967296# + lHigh, lHigh )
returnValue = returnValue * 4294967296#
returnValue = returnValue + IIf( lLow < 0, 4294967296 + lLow, lLow )
GetDoubleFromTwoLongs = returnValue
End Function
' In order to combine this values in C, the following code can be used:
' ULONGLONG ullValue = ( ( ( ULONGLONG )lSizeHigh ) << 32 ) + ( ( ULONGLONG )lSizeLow ); |
In Delphi, these values can be combined in the following manner:
| Delphi |
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var
lSizeLow : LongInt;
lSizeHigh : LongInt;
llSize : Int64;
begin
{ Value examples }
lSizeLow := -1;
lSizeHigh := 1;
{ How to convert two signed 32-bit values to an Int64 }
llSize := ( Int64( Longword( lSizeHigh ) ) shl 32 ) + ( Int64( Longword( lSizeLow ) ) ); |
The following example demonstrates how to get two long values from a 64-bit integer. The values retrieved can then be assigned to the
SplitSize and
SplitSizeHigh values when creating split zip files.
| Visual Basic |
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Private Sub GetTwoLongsFromInt64(ByVal cInt64 As Currency, ByRef lHigh As Long, ByRef lLow As Long)
Dim cRemainder As Currency
' Compute what multiple of &H7FFFFFFF the supplied 64-bit value
lHigh = CLng(Fix(cInt64 / 4294967296#))
' In an ideal world, the Mod operator would be used to compute the remainder.
' Unfortunately, in VB6 it casts its operand to Long so most attempts will overflow
' We will therefore find the remainder by substracting the high part from the 64-bit value
cRemainder = cInt64 - (lHigh * 4294967296#)
' If the remaining value is smaller or equal than a signed 32 bit value (&H7FFFFFFF)
If (cRemainder <= 2147483647#) Then
' Use the remaining value as the low part
lLow = CLng(cRemainder)
Else
' Wrap the remaining value around so it expresses as a signed 32 bit value
cRemainder = cRemainder - 4294967296#
' Use the transformed remaining value as the low part
lLow = (CLng(cRemainder))
End If
End Sub
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