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<div class=Section1>
<p class=MsoNormal><span style='mso-tab-count:2'> </span><b
style='mso-bidi-font-weight:normal'><span style='font-size:14.0pt'>Encode and
Decode HDF5 Objects<o:p></o:p></span></b></p>
<p class=MsoNormal><span style='mso-tab-count:3'> </span><b
style='mso-bidi-font-weight:normal'>Raymond Lu & <span class=SpellE>Quincey</span>
<span class=SpellE>Koziol</span><o:p></o:p></b></p>
<p class=MsoNormal><span style='mso-tab-count:3'> </span><st1:date
Month="7" Day="27" Year="2004">July 27, 2004</st1:date></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal style='margin-left:.75in;text-indent:-.5in;mso-list:l0 level1 lfo1;
tab-stops:list .75in'><![if !supportLists]><b style='mso-bidi-font-weight:normal'><span
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style='font:7.0pt "Times New Roman"'>
</span></span></span></b><![endif]><b style='mso-bidi-font-weight:normal'>Documents
Audience<o:p></o:p></b></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span class=GramE>Current HDF5 library designers and
knowledgeable external developers.</span></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal style='margin-left:.75in;text-indent:-.5in;mso-list:l0 level1 lfo1;
tab-stops:list .75in'><![if !supportLists]><b style='mso-bidi-font-weight:normal'><span
style='mso-fareast-font-family:"Times New Roman"'><span style='mso-list:Ignore'>II.<span
style='font:7.0pt "Times New Roman"'>
</span></span></span></b><![endif]><b style='mso-bidi-font-weight:normal'>Functionality<o:p></o:p></b></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The functions described in this document encode and decode
the description of HDF5 objects given by their ID into a binary buffer.<span
style='mso-spacerun:yes'> </span>At this stage, these functions deal only with
datatype and dataspace objects.<span style='mso-spacerun:yes'> </span>In the
future, we may expand the coverage of the objects.</p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal style='margin-left:.75in;text-indent:-.5in;mso-list:l0 level1 lfo1;
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style='mso-fareast-font-family:"Times New Roman"'><span style='mso-list:Ignore'>III.<span
style='font:7.0pt "Times New Roman"'>
</span></span></span></b><![endif]><b style='mso-bidi-font-weight:normal'>Motivations
and Use Cases<o:p></o:p></b></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The motivation of these functions is to provide a way to
transmit object description between two tasks.<span style='mso-spacerun:yes'>
</span>The second task can reconstruct the object and return its ID.<span
style='mso-spacerun:yes'> </span>This can happen among different processes in
an MPI program.<span style='mso-spacerun:yes'> </span>Another useful case is
to do checksum on the object.<span style='mso-spacerun:yes'> </span></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>It is possible to allow users program to decode the binary
description of the object if there is need to do so.<span
style='mso-spacerun:yes'> </span>See below for a description of the encoding
of the objects.</p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Below are some use cases (borrowed from Robb Matzke),</p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>1.<span style='mso-spacerun:yes'> </span>In a parallel
program (plain old PHDF5 and not FPHDF5) datasets must be created collectively
over the file communicator, but sometimes conceptually only one MPI task (call
it the "root" task) wants to create the object. Therefore the
non-root tasks need to jump into the <span class=GramE><span style='font-size:
10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>H5Dcreate(</span></span><span
style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>)</span>
call too, and they need to all supply various parameters including a datatype. <span
style='mso-spacerun:yes'></span>HDF5 <span class=SpellE>datatypes</span> have
such a rich expressive power that it would be easiest if HDF5 provided some way
to help the root task broadcast the datatype to the other tasks rather than the
programmer dissect the datatype, broadcast its description, then construct it
on the other tasks. That's where the encode/decode functions come in: the
encode takes a datatype and converts it into some task-independent
representation</p>
<p class=MsoNormal><span class=GramE>that</span> can be broadcast to the other
tasks, which then decode that representation back into an <span class=SpellE><i
style='mso-bidi-font-style:normal'>hid_t</i></span> handle to a datatype.</p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>2.<span style='mso-spacerun:yes'> </span>This second use
case is similar in that one MPI task has a datatype that it would like to save
in a file. Normally <span class=GramE><span style='font-size:10.0pt;font-family:
"Courier New";mso-bidi-font-family:"Times New Roman"'>H5Tcommit(</span></span><span
style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>)</span>
is a file-collective operation. However, writing to an existing dataset is
independent, so a programmer could encode a datatype into the</p>
<p class=MsoNormal><span class=GramE>task-independent</span> representation and
independently write that into an existing dataset. Obviously in this situation
a reader program would have to know that the sequence of bytes is an encoded
datatype in order to do anything useful with it.</p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>3.<span style='mso-spacerun:yes'> </span>In order to
compare whether two <span class=SpellE>datatypes</span> on different tasks are
equivalent you could byte-compare their task-independent encodings.</p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>4.<span style='mso-spacerun:yes'> </span>If you have <i
style='mso-bidi-font-style:normal'>lots</i> of <span class=SpellE>datatypes</span>
to compare (e.g., sorting an array of <span class=SpellE>datatypes</span>) it
would probably be faster to encode them all first, then sort based on the
encoding since <span class=SpellE><span class=GramE><span style='font-size:
10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>memcmp</span></span></span><span
class=GramE><span style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:
"Times New Roman"'>(</span></span><span style='font-size:10.0pt;font-family:
"Courier New";mso-bidi-font-family:"Times New Roman"'>)</span> is almost certainly
faster than <span style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:
"Times New Roman"'>H5T_cmp().</span></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>5.<span style='mso-spacerun:yes'> </span>If you have <i
style='mso-bidi-font-style:normal'>lots</i> of <span class=SpellE>datatypes</span>
to save in a file and those types are distributed among MPI tasks then its
probably fastest to have each task encode its <span class=SpellE>datatypes</span>,
<span class=SpellE><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'>MPI_Gather</span></span><span
style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>()</span>
them to a single I/O task, then that task independently writes the encoded
types to a</p>
<p class=MsoNormal><span class=GramE>pre-existing</span> dataset.</p>
<p class=MsoNormal><span style='mso-spacerun:yes'></span></p>
<p class=MsoNormal style='margin-left:.75in;text-indent:-.5in;mso-list:l0 level1 lfo1;
tab-stops:list .75in'><![if !supportLists]><b style='mso-bidi-font-weight:normal'><span
style='mso-fareast-font-family:"Times New Roman"'><span style='mso-list:Ignore'>IV.<span
style='font:7.0pt "Times New Roman"'>
</span></span></span></b><![endif]><b style='mso-bidi-font-weight:normal'>Release<o:p></o:p></b></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>There functions are for release 1.8 of the library.<o:p></o:p></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><o:p> </o:p></b></p>
<p class=MsoNormal style='margin-left:.75in;text-indent:-.5in;mso-list:l0 level1 lfo1;
tab-stops:list .75in'><![if !supportLists]><b style='mso-bidi-font-weight:normal'><span
style='mso-fareast-font-family:"Times New Roman"'><span style='mso-list:Ignore'>V.<span
style='font:7.0pt "Times New Roman"'>
</span></span></span></b><![endif]><b style='mso-bidi-font-weight:normal'>Algorithms
& Format of Data<o:p></o:p></b></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><o:p> </o:p></b></p>
<p class=MsoNormal>For the internal library design, we are going to borrow the
algorithm of encoding and decoding object header messages.<span
style='mso-spacerun:yes'> </span>It will be helpful to take a look at the data
object part (Part IV) of the HDF5 File Format document.<span
style='mso-spacerun:yes'> </span>The data objects we are interested in here
are datatype and dataspace.<o:p></o:p></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><o:p> </o:p></b></p>
<p class=MsoNormal>Format of the datatype information:</p>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>The encoded
datatype is composed of the following information:</p>
<p class=MsoNormal style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1;
tab-stops:list 1.0in'><![if !supportLists]><span style='font-family:Symbol;
mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol'><span
style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]>A single byte indicating the buffer is a
datatype which is the same value (3) as the datatype message ID in object
headers in the file format.</p>
<p class=MsoNormal style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1;
tab-stops:list 1.0in'><![if !supportLists]><span style='font-family:Symbol;
mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol'><span
style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]>A single byte indicating the version of the
datatype information, currently set to 0.</p>
<p class=MsoNormal style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1;
tab-stops:list 1.0in'><![if !supportLists]><span style='font-family:Symbol;
mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol'><span
style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]>A sequence of bytes that have the same format as
the datatype message in the object header.<span style='mso-spacerun:yes'>
</span>See the HDF5 file format document for the exact format.</p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Format of the dataspace information:</p>
<p class=MsoNormal><span style='mso-tab-count:1'> </span>The encoded
dataspace is composed of the following information:</p>
<p class=MsoNormal style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1;
tab-stops:list 1.0in'><![if !supportLists]><span style='font-family:Symbol;
mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol'><span
style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]>A single byte indicating the buffer is a
dataspace which is the same value (1) as the dataspace message ID in object
headers in the file format.</p>
<p class=MsoNormal style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1;
tab-stops:list 1.0in'><![if !supportLists]><span style='font-family:Symbol;
mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol'><span
style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]>A single byte indicating the version of the
dataspace information, currently set to 0.</p>
<p class=MsoNormal style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1;
tab-stops:list 1.0in'><![if !supportLists]><span style='font-family:Symbol;
mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol'><span
style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]>A single indicating the size in bytes of the
size of lengths information for the rest of the information encoded in the
buffer.</p>
<p class=MsoNormal style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1;
tab-stops:list 1.0in'><![if !supportLists]><span style='font-family:Symbol;
mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol'><span
style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]>A 16-bit value indicating the size in bytes of
the dataspace extent information.</p>
<p class=MsoNormal style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1;
tab-stops:list 1.0in'><![if !supportLists]><span style='font-family:Symbol;
mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol'><span
style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]>A sequence of bytes that store the extent of the
dataspace and that have the same format as the dataspace message in the object
header.<span style='mso-spacerun:yes'> </span>See the HDF5 file format
document for the exact format.</p>
<p class=MsoNormal style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo1;
tab-stops:list 1.0in'><![if !supportLists]><span style='font-family:Symbol;
mso-fareast-font-family:Symbol;mso-bidi-font-family:Symbol'><span
style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]>A sequence of bytes that store the selection
within the dataspace and that have the same format as the region portion of a
region reference.<span style='mso-spacerun:yes'> </span>See the HDF5 file
format document for the exact format.</p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><o:p> </o:p></b></p>
<p class=MsoNormal style='margin-left:.75in;text-indent:-.5in;mso-list:l0 level1 lfo1;
tab-stops:list .75in'><![if !supportLists]><b style='mso-bidi-font-weight:normal'><span
style='mso-fareast-font-family:"Times New Roman"'><span style='mso-list:Ignore'>VI.<span
style='font:7.0pt "Times New Roman"'>
</span></span></span></b><![endif]><b style='mso-bidi-font-weight:normal'>Examples<o:p></o:p></b></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><o:p> </o:p></b></p>
<p class=MsoNormal>Here is an example for <span class=GramE><span
style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>H5Tencode(</span></span><span
style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>)</span>
and <span style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:
"Times New Roman"'>H5Tdecode()</span>.<span style='mso-spacerun:yes'>
</span>In this piece of code, it creates a compound datatype and encodes
it.<span style='mso-spacerun:yes'> </span>Then it decodes the buffer and
returns a new object ID.<span style='mso-spacerun:yes'> </span></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>struct</span></span> s1 {<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>int</span></span><span
style='mso-spacerun:yes'> </span>a;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>float<span style='mso-spacerun:yes'> </span>b</span>;<o:p></o:p></span></p>
<p class=MsoNormal style='text-indent:24.0pt'><span style='font-size:10.0pt;
font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>};<o:p></o:p></span></p>
<p class=MsoNormal style='text-indent:24.0pt'><span class=GramE><span
style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>hid</span></span><span
style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>
tid1, decoded_tid1;<o:p></o:p></span></p>
<p class=MsoNormal style='text-indent:24.0pt'><span style='font-size:10.0pt;
font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'><span
style='mso-tab-count:2'> </span>:<o:p></o:p></span></p>
<p class=MsoNormal style='text-indent:24.0pt'><span style='font-size:10.0pt;
font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span>/* <span class=GramE>Create</span> a compound datatype */<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>if(</span>(tid1=H5Tcreate(H5T_COMPOUND, <span
class=SpellE>sizeof</span>(<span class=SpellE>struct</span> s1)))<0) <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>goto</span></span> error;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>if(</span>H5Tinsert(tid1, "a", HOFFSET(<span
class=SpellE>struct</span> s1, a), H5T_NATIVE_INT)<0)<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>goto</span></span> error;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>if(</span>H5Tinsert(tid1, "b", HOFFSET(<span
class=SpellE>struct</span> s1, b), H5T_NATIVE_FLOAT)<0)<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>goto</span></span> error;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span>/* <span class=GramE>Encode</span> compound type in a buffer */<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>if(</span>H5Tencode(tid1, NULL, &<span
class=SpellE>cmpd_buf_size</span>)<0)<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>goto</span></span> error;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>if(</span><span class=SpellE>cmpd_buf_size</span>>0)<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE>cmpd_buf</span> = (unsigned char*<span class=GramE>)<span
class=SpellE>calloc</span></span>(1, <span class=SpellE>cmpd_buf_size</span>);<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>if(</span>H5Tencode(tid1, <span class=SpellE>cmpd_buf</span>,
&<span class=SpellE>cmpd_buf_size</span>)<0)<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>goto</span></span> error;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span>/* <span class=GramE>Decode</span> from the compound buffer and return
an object handle */<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>if(</span>(decoded_tid1=H5Tdecode(<span class=SpellE>cmpd_buf</span>))<0)<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>goto</span></span> error;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal>Below is an example for encoding and decoding a simple
dataspace using <span class=GramE><span style='font-size:10.0pt;font-family:
"Courier New";mso-bidi-font-family:"Times New Roman"'>H5Sencode(</span></span><span
style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>)</span>
and <span style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:
"Times New Roman"'>H5Sdecode()</span>.<span style='mso-spacerun:yes'>
</span>Notice that dataspace <span class=GramE>selection(</span><span
class=SpellE>hyperslab</span> in this case) can also be encoded and decoded.<o:p></o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal style='text-indent:24.0pt'><span class=SpellE><span
style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>hid_t</span></span><span
style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'><span
style='mso-tab-count:1'> </span>sid1, decoded_sid1;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span style='mso-spacerun:yes'></span><span class=SpellE>hsize_t</span><span
style='mso-spacerun:yes'> </span><span class=GramE>dims1[</span>] =
{3, 15, 13};<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>hssize_t</span></span><span
style='mso-spacerun:yes'> </span>start[] = {0, 0, 0};<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>hsize_t</span></span><span
style='mso-spacerun:yes'> </span>stride[] = {2, 5, 3};<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>hsize_t</span></span><span
style='mso-spacerun:yes'> </span>count[] = {2, 2, 2};<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>hsize_t</span></span><span
style='mso-spacerun:yes'> </span>block[] = {1, 3, 1};<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span>/* <span class=GramE>Create</span> a simple data space of 3x15x13 */<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span>sid1 = H5Screate_<span class=GramE>simple(</span>SPACE1_RANK, dims1,
NULL);<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>CHECK(</span>sid1, FAIL,
"H5Screate_simple");<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-tab-count:1'> </span><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span>/* Make a <span class=SpellE>hyperslab</span> selection */<o:p></o:p></span></p>
<p class=MsoNormal style='text-indent:24.0pt'><span class=GramE><span
style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>ret</span></span><span
style='font-size:10.0pt;font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'>
= H5Sselect_hyperslab(sid1, H5S_SELECT_SET, start, stride,<o:p></o:p></span></p>
<p class=MsoNormal style='text-indent:24.0pt'><span style='font-size:10.0pt;
font-family:"Courier New";mso-bidi-font-family:"Times New Roman"'><span
style='mso-tab-count:2'> </span><span class=GramE>count</span>, block);<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>CHECK(</span>ret, FAIL,
"H5Sselect_hyperslab");<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span>/* Find out the size of buffer needed for encoding */<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>ret</span> = H5Sencode(sid1, NULL, &<span
class=SpellE>sbuf_size</span>);<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>CHECK(</span>ret, FAIL, "H5Sencode");<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>if(</span><span class=SpellE>sbuf_size</span>>0)<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=SpellE><span class=GramE>sbuf</span></span> = (unsigned
char*)<span class=SpellE>calloc</span>(1, <span class=SpellE>sbuf_size</span>);<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span>/* <span class=GramE>Encode</span> simple data space in a buffer */<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>ret</span> = H5Sencode(sid1, <span class=SpellE>sbuf</span>,
&<span class=SpellE>sbuf_size</span>);<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>CHECK(</span>ret, FAIL, "H5Sencode");<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span>/* <span class=GramE>Decode</span> from the dataspace buffer and return
an object handle */<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span>decoded_sid1=<span class=GramE>H5Sdecode(</span><span class=SpellE>sbuf</span>);<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
mso-bidi-font-family:"Times New Roman"'><span style='mso-spacerun:yes'>
</span><span class=GramE>CHECK(</span>decoded_sid1, FAIL, "H5Sdecode");<o:p></o:p></span></p>
<p class=MsoNormal><b style='mso-bidi-font-weight:normal'><o:p> </o:p></b></p>
<p class=MsoNormal style='margin-left:.75in;text-indent:-.5in;mso-list:l0 level1 lfo1;
tab-stops:list .75in'><![if !supportLists]><b style='mso-bidi-font-weight:normal'><span
style='mso-fareast-font-family:"Times New Roman"'><span style='mso-list:Ignore'>VII.<span
style='font:7.0pt "Times New Roman"'>
</span></span></span></b><![endif]><b style='mso-bidi-font-weight:normal'>API
Functions<o:p></o:p></b></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><strong>Name:</strong> <a name=Dataset-GetType>H5</a>Tencode</p>
<p class=MsoNormal><strong>Signature:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'><span class=SpellE><em>herr_<span
class=GramE>t</span></em></span><span class=GramE><em><span
style='mso-spacerun:yes'> </span></em><code><span style='font-size:10.0pt'>H5Tencode</span></code></span>(<span
class=SpellE><em>hid_t</em></span><em> </em><span class=SpellE><code><span
style='font-size:10.0pt'>obj_id</span></code></span><code><span
style='font-size:10.0pt'>, </span></code><code><i style='mso-bidi-font-style:
normal'><span style='mso-ansi-font-size:12.0pt;mso-bidi-font-size:12.0pt;
font-family:"Times New Roman"'>unsigned char*</span></i></code><code><span
style='font-size:10.0pt'> <span class=SpellE>buf</span>, </span></code><span
class=SpellE><code><i style='mso-bidi-font-style:normal'><span
style='mso-ansi-font-size:12.0pt;mso-bidi-font-size:12.0pt;font-family:"Times New Roman"'>size_t</span></i></code></span><code><i
style='mso-bidi-font-style:normal'><span style='mso-ansi-font-size:12.0pt;
mso-bidi-font-size:12.0pt;font-family:"Times New Roman"'>*</span></i></code><code><span
style='font-size:10.0pt'> <span class=SpellE>nalloc</span></span></code>) </p>
<p class=MsoNormal><strong>Purpose:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'>Encode a data type object
description into a binary buffer. </p>
<p class=MsoNormal><strong>Description:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'>Given data type ID, <span
style='font-size:10.0pt;font-family:"Courier New"'>H5Tencode</span> converts a data
type description into binary form in a buffer.<span style='mso-spacerun:yes'>
</span>Using this binary form in the buffer, a data type object can be
reconstructed using <span style='font-size:10.0pt;font-family:"Courier New"'>H5Tdecode</span>
to return a new object <span class=GramE>handle(</span><span class=SpellE><i
style='mso-bidi-font-style:normal'>hid_t</i></span>) for this data type.</p>
<p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p>
<p class=MsoNormal style='margin-left:.5in'>A preliminary <code><span
style='font-size:10.0pt'>H5Tencode</span></code> call can be made to find out
the size of the buffer needed. This value is returned as <span class=SpellE><span
style='font-size:10.0pt;font-family:"Courier New"'>nalloc</span></span>.<span
style='mso-spacerun:yes'> </span>That value can then be assigned to <span
class=SpellE><code><span style='font-size:10.0pt'>nalloc</span></code></span>
for a second <code><span style='font-size:10.0pt'>H5Tencode</span></code> call,
which will retrieve the actual encoded object.<span style='mso-spacerun:yes'>
</span></p>
<p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p>
<p class=MsoNormal style='margin-left:.5in'>If the library finds out <span
class=SpellE><span style='font-size:10.0pt;font-family:"Courier New"'>nalloc</span></span>
is not big enough for the object, it simply returns the size of the buffer
needed through <span class=SpellE><span style='font-size:10.0pt;font-family:
"Courier New"'>nalloc</span></span> without encoding the provided buffer.<strong><span
style='font-weight:normal'><o:p></o:p></span></strong></p>
<p class=MsoNormal><strong>Parameters:</strong> </p>
<p class=MsoNormal><span class=SpellE><em>hid_t</em></span> <span class=SpellE><code><span
style='font-size:10.0pt'>obj_id</span></code></span> </p>
<p class=MsoNormal style='margin-left:.5in'>IN: Identifier of the object to be
encoded.</p>
<p class=MsoNormal><span class=GramE><em>unsigned</em></span><em> char*</em> <span
class=SpellE><code><span style='font-size:10.0pt'>buf</span></code></span> </p>
<p class=MsoNormal style='margin-left:.5in'>IN/OUT: Buffer for the object to be
encoded into.<span style='mso-spacerun:yes'> </span>If the provided buffer is
NULL, </p>
<p class=MsoNormal style='margin-left:.5in'><span class=GramE>only</span> the
size of buffer needed is returned through <span class=SpellE><span
style='font-size:10.0pt;font-family:"Courier New"'>nalloc</span></span>. </p>
<p class=MsoNormal><span class=SpellE><em>size_t</em></span><em>*</em> <span
class=SpellE><code><span style='font-size:10.0pt'>nalloc</span></code></span> </p>
<p class=MsoNormal style='margin-left:.5in'>IN: The size of the allocated
buffer.</p>
<p class=MsoNormal style='margin-left:.5in'>OUT: The size of the buffer needed.
</p>
<p class=MsoNormal><strong>Returns:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'>Returns a non-negative value if
successful; otherwise returns a negative value.</p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><strong>Name:</strong> H5Tdecode</p>
<p class=MsoNormal><strong>Signature:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'><span class=SpellE><em>hid_<span
class=GramE>t</span></em></span><span class=GramE><em><span
style='mso-spacerun:yes'> </span></em><code><span style='font-size:10.0pt'>H5Tdecode</span></code></span>(<code><i
style='mso-bidi-font-style:normal'><span style='mso-ansi-font-size:12.0pt;
mso-bidi-font-size:12.0pt;font-family:"Times New Roman"'>unsigned char*</span></i></code><code><span
style='font-size:10.0pt'> <span class=SpellE>buf</span></span></code>) </p>
<p class=MsoNormal><strong>Purpose:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'>Decode a binary object description of
data type and return a new object handle. </p>
<p class=MsoNormal><strong>Description:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'>Given an object description of data
type in binary in a buffer, <span style='font-size:10.0pt;font-family:"Courier New"'>H5Tdecode</span>
reconstructs the HDF5 data type object and returns a new object handle for
it.<span style='mso-spacerun:yes'> </span>The binary description of the object
is encoded by <span style='font-size:10.0pt;font-family:"Courier New"'>H5Tencode</span>.<span
style='mso-spacerun:yes'> </span>User is responsible for passing in the right
buffer.</p>
<p class=MsoNormal><strong>Parameters:</strong> </p>
<p class=MsoNormal><span class=GramE><em>unsigned</em></span><em> char*</em> <span
class=SpellE><code><span style='font-size:10.0pt'>buf</span></code></span> </p>
<p class=MsoNormal style='margin-left:.5in'>IN: Buffer for the data type object
to be decoded. </p>
<p class=MsoNormal><strong>Returns:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'>Returns an object <span
class=GramE>ID(</span>non-negative) if successful; otherwise returns a negative
value.</p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><strong>Name:</strong> H5Sencode</p>
<p class=MsoNormal><strong>Signature:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'><span class=SpellE><em>herr_<span
class=GramE>t</span></em></span><span class=GramE><em><span
style='mso-spacerun:yes'> </span></em><code><span style='font-size:10.0pt'>H5Sencode</span></code></span>(<span
class=SpellE><em>hid_t</em></span><em> </em><span class=SpellE><code><span
style='font-size:10.0pt'>obj_id</span></code></span><code><span
style='font-size:10.0pt'>, </span></code><code><i style='mso-bidi-font-style:
normal'><span style='mso-ansi-font-size:12.0pt;mso-bidi-font-size:12.0pt;
font-family:"Times New Roman"'>unsigned char*</span></i></code><code><span
style='font-size:10.0pt'> <span class=SpellE>buf</span>, </span></code><span
class=SpellE><code><i style='mso-bidi-font-style:normal'><span
style='mso-ansi-font-size:12.0pt;mso-bidi-font-size:12.0pt;font-family:"Times New Roman"'>size_t</span></i></code></span><code><i
style='mso-bidi-font-style:normal'><span style='mso-ansi-font-size:12.0pt;
mso-bidi-font-size:12.0pt;font-family:"Times New Roman"'>*</span></i></code><code><span
style='font-size:10.0pt'> <span class=SpellE>nalloc</span></span></code>) </p>
<p class=MsoNormal><strong>Purpose:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'>Encode a data space object
description into a binary buffer. </p>
<p class=MsoNormal><strong>Description:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'>Given the data space ID, <span
style='font-size:10.0pt;font-family:"Courier New"'>H5Sencode</span> converts a
data space description into binary form in a buffer.<span
style='mso-spacerun:yes'> </span>Using this binary form in the buffer, a data
space object can be reconstructed using <span style='font-size:10.0pt;
font-family:"Courier New"'>H5Sdecode</span> to return a new object <span
class=GramE>handle(</span><span class=SpellE><i style='mso-bidi-font-style:
normal'>hid_t</i></span>) for this data space.</p>
<p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p>
<p class=MsoNormal style='margin-left:.5in'>A preliminary <code><span
style='font-size:10.0pt'>H5Sencode</span></code> call can be made to find out
the size of the buffer needed. This value is returned as <span class=SpellE><span
style='font-size:10.0pt;font-family:"Courier New"'>nalloc</span></span>.<span
style='mso-spacerun:yes'> </span>That value can then be assigned to <span
class=SpellE><code><span style='font-size:10.0pt'>nalloc</span></code></span>
for a second <code><span style='font-size:10.0pt'>H5Sencode</span></code> call,
which will retrieve the actual encoded object.<span style='mso-spacerun:yes'>
</span></p>
<p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p>
<p class=MsoNormal style='margin-left:.5in'>If the library finds out <span
class=SpellE><span style='font-size:10.0pt;font-family:"Courier New"'>nalloc</span></span>
is not big enough for the object, it simply returns the size of the buffer
needed through <span class=SpellE><span style='font-size:10.0pt;font-family:
"Courier New"'>nalloc</span></span> without encoding the provided buffer.</p>
<p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p>
<p class=MsoNormal style='margin-left:.5in'><strong><span style='font-weight:
normal'>The types of data space we address in this function are null, scalar,
and simple space.<span style='mso-spacerun:yes'> </span>For simple data space,
the information of selection, for example, <span class=SpellE>hyperslab</span> <span
class=GramE>selection,</span> is also encoded and decoded.<span
style='mso-spacerun:yes'> </span>Complex data space has not been implemented
in the library.<o:p></o:p></span></strong></p>
<p class=MsoNormal><strong>Parameters:</strong> </p>
<p class=MsoNormal><span class=SpellE><em>hid_t</em></span> <span class=SpellE><code><span
style='font-size:10.0pt'>obj_id</span></code></span> </p>
<p class=MsoNormal style='margin-left:.5in'>IN: Identifier of the object to be
encoded.</p>
<p class=MsoNormal><span class=GramE><em>unsigned</em></span><em> char*</em> <span
class=SpellE><code><span style='font-size:10.0pt'>buf</span></code></span> </p>
<p class=MsoNormal style='margin-left:.5in'>IN/OUT: Buffer for the object to be
encoded into.<span style='mso-spacerun:yes'> </span>If the provided buffer is
NULL, </p>
<p class=MsoNormal style='margin-left:.5in'><span class=GramE>only</span> the
size of buffer needed is returned through <span class=SpellE><span
style='font-size:10.0pt;font-family:"Courier New"'>nalloc</span></span>. </p>
<p class=MsoNormal><span class=SpellE><em>size_t</em></span><em>*</em> <span
class=SpellE><code><span style='font-size:10.0pt'>nalloc</span></code></span> </p>
<p class=MsoNormal style='margin-left:.5in'>IN: The size of the allocated
buffer.</p>
<p class=MsoNormal style='margin-left:.5in'>OUT: The size of the buffer needed.
</p>
<p class=MsoNormal><strong>Returns:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'>Returns a non-negative value if
successful; otherwise returns a negative value.</p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><strong>Name:</strong> H5Sdecode</p>
<p class=MsoNormal><strong>Signature:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'><span class=SpellE><em>hid_<span
class=GramE>t</span></em></span><span class=GramE><em><span
style='mso-spacerun:yes'> </span></em><code><span style='font-size:10.0pt'>H5Sdecode</span></code></span>(<code><i
style='mso-bidi-font-style:normal'><span style='mso-ansi-font-size:12.0pt;
mso-bidi-font-size:12.0pt;font-family:"Times New Roman"'>unsigned char*</span></i></code><code><span
style='font-size:10.0pt'> <span class=SpellE>buf</span></span></code>) </p>
<p class=MsoNormal><strong>Purpose:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'>Decode a binary object description
of data space and return a new object handle. </p>
<p class=MsoNormal><strong>Description:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'>Given an object description of data
space in binary in a buffer, <span style='font-size:10.0pt;font-family:"Courier New"'>H5Sdecode</span>
reconstructs the HDF5 data type object and returns a new object handle for
it.<span style='mso-spacerun:yes'> </span>The binary description of the object
is encoded by <span style='font-size:10.0pt;font-family:"Courier New"'>H5Sencode</span>.<span
style='mso-spacerun:yes'> </span>User is responsible for passing in the right
buffer.</p>
<p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p>
<p class=MsoNormal style='margin-left:.5in'><strong><span style='font-weight:
normal'>The types of data space we address in this function are null, scalar,
and simple space.<span style='mso-spacerun:yes'> </span>For simple data space,
the information of selection, for example, <span class=SpellE>hyperslab</span> <span
class=GramE>selection,</span> is also encoded and decoded.<span
style='mso-spacerun:yes'> </span>Complex data space has not been implemented
in the library.<o:p></o:p></span></strong></p>
<p class=MsoNormal><strong>Parameters:</strong> </p>
<p class=MsoNormal><span class=GramE><em>unsigned</em></span><em> char*</em> <span
class=SpellE><code><span style='font-size:10.0pt'>buf</span></code></span> </p>
<p class=MsoNormal style='margin-left:.5in'>IN: Buffer for the data space
object to be decoded. </p>
<p class=MsoNormal><strong>Returns:</strong> </p>
<p class=MsoNormal style='margin-left:.5in'>Returns an object <span
class=GramE>ID(</span>non-negative) if successful; otherwise returns a negative
value.</p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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