🚀 go-pugleaf

I want to read a Macpaint file, unpack the bit image and write out the unpacked
bits to a file.  Simply enough, right?  But IM sez 

	UnpackBits (VAR srcPtr, dstPtr: Ptr; dstBytes: INTEGER);

where dstBytes is the length that the expanded data will be; it should be the
value that was passed to PackBits.  Now, I don't know what that value is.  Can
anyone give me a hint on how to find out this value.  IM sez srcPtr will be 
incremented the number of expanded bytes, but that doesn't help me.  I
read the file ok and then do an lseek() to set the file cursor past the header 
stuff.   Thanks in advance.  I hope this isn't a stupid question!

--Bill

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