[SQUASH ME] Added additional text explaining 31-bit vs 32-bit size li…

…mits.

The main tables should describe sign and on-disk sizes, which they now
do, but on disk size is not the same thing as range of valid values.

I feel this is clearer than the alternative option of keeping some as
int32_t and needing to define their valid ranges.

SAMv1.tex

@@ -947,6 +947,14 @@ \subsection{The BAM format}
 the default when the corresponding information is not available; an
 underlined word in uppercase denotes a field in the SAM format.
 
+Note the field types defined below define whether the value may be
+negative and the number of bytes used on disk, but do not necessarily
+dictate their appropriate maximum value.  Care should be taken with
+{\tt uint32\_t} fields to avoid exceeding 31-bits (approximately 2 billion)
+as this can cause either implementation language issues or other
+related data type constraints (e.g. {\tt tlen} needs to be 1 bit larger
+than the maximum {\tt l\_ref}).
+
 \begin{table}[ht]
 \centering
 {\small
@@ -1076,7 +1084,7 @@ \subsubsection{Auxiliary data encoding}\label{sec:aux-type-codes}
 \newcommand*{\arraytagfield}[3]{\tagfield{B}{\bytebox{1}{\tt #1}\bytebox{4}{\em count}\byteboxvector{#2}{#3}}}
 
 The representation of a `{\tt B}' array field starts with a sub-type character
-similar to the numeric field types above and an {\tt uint32\_t} \emph{count}
+similar to the numeric field types above and a {\tt uint32\_t} \emph{count}
 giving the number of elements in the array.
 The array elements follow, encoded as binary integers or IEEE floats sized
 according to the sub-type:
@@ -1220,6 +1228,11 @@ \subsection{The BAI index format for BAM files}
 \end{tabular}}
 \end{table}
 
+As with the BAM format, the {\tt uint32\_t} fields indicate unsigned
+values consuming 4 bytes and do not imply the full range of values is
+appropriate.  Practical implementations may limit these to 31-bit or
+less.
+
 The index file may optionally contain additional metadata providing a summary
 of the number of mapped and unmapped read-segments per reference sequence,
 and of any unplaced unmapped read-segments.\footnote{By \emph{placed unmapped