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@@ -4357,7 +4357,11 @@ The problem of distinguishing between pointers and other kinds of data
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also arises inside of each tuple. We solve this problem by attaching a
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tag, an extra 64-bits, to each tuple. Figure~\ref{fig:tuple-rep} zooms
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in on the tags for two of the tuples in the example from
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-Figure~\ref{fig:copying-collector}. Part of each tag is dedicated to
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+Figure~\ref{fig:copying-collector}. Note that we have drawn the bits
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+in a big-endian way, from right-to-left, with bit location 0 (the
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+least significant bit) on the far right, which corresponds to the
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+directionality of the x86 shifting instructions \key{salq} (shift
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+left) and \key{sarq} (shift right). Part of each tag is dedicated to
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specifying which elements of the tuple are pointers, the part labeled
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``pointer mask''. Within the pointer mask, a 1 bit indicates there is
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a pointer and a 0 bit indicates some other kind of data. The pointer
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@@ -4366,10 +4370,10 @@ size of 50 elements, so we just need 50 bits for the pointer mask. The
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tag also contains two other pieces of information. The length of the
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tuple (number of elements) is stored in bits location 1 through
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6. Finally, the bit at location 0 indicates whether the tuple has yet
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-to be copied to the ToSpace. If the bit has value 1, then this
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-tuple has not yet been copied. If the bit has value 0 then the entire
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-tag is in fact a forwarding pointer. (The lower 3 bits of an pointer
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-are always zero anyways because our tuples are 8-byte aligned.)
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+to be copied to the ToSpace. If the bit has value 1, then this tuple
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+has not yet been copied. If the bit has value 0 then the entire tag
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+is in fact a forwarding pointer. (The lower 3 bits of an pointer are
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+always zero anyways because our tuples are 8-byte aligned.)
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\begin{figure}[tbp]
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\centering \includegraphics[width=0.8\textwidth]{figs/tuple-rep}
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Jeremy Siek