<section id="vorbis-spec-residue">
<sectioninfo>
<releaseinfo>
- $Id: 08-residue.xml,v 1.4 2002/10/27 16:20:47 giles Exp $
- <emphasis>Last update to this document: July 19, 2002</emphasis>
+ $Id: 08-residue.xml,v 1.5 2003/03/11 11:02:17 xiphmont Exp $
+ <emphasis>Last update to this document: March 11, 2003</emphasis>
</releaseinfo>
</sectioninfo>
<title>Residue setup and decode</title>
the decode process:</para>
<programlisting>
- 1) [classvals_per_codeword] = [codebook_dimensions] value of codebook [residue_classbook]
- 2) [n_to_read] = [residue_end] - [residue-begin]
+ 1) [classwords_per_codeword] = [codebook_dimensions] value of codebook [residue_classbook]
+ 2) [n_to_read] = [residue_end] - [residue_begin]
3) [partitions_to_read] = [n_to_read] / [residue_partition_size]
</programlisting>
2) iterate [pass] over the range 0 ... 7 {
3) [partition_count] = 0
+
4) if ([pass] is zero) {
5) iterate [j] over the range 0 .. [ch]-1 {
6) if vector [j] is not marked 'do not decode' {
7) [temp] = read from packet using codebook [residue_classbook] in scalar context
- 8) iterate [k] descending over the range [classvals_per_codeword]-1 ... 0 {
+ 8) iterate [i] descending over the range [classwords_per_codeword]-1 ... 0 {
- 9) array [classifications] element [j],([partition_count]+[k]) =
+ 9) array [classifications] element [j],([i]+[partition_count]) =
[temp] integer modulo [residue_classifications]
10) [temp] = [temp] / [residue_classifications] using integer division
}
- 11) [classword_count] = 0
- 12) iterate [j] over the range 0 .. [ch]-1 {
-
- 13) if vector [j] is not marked 'do not decode' {
+ 11) iterate [i] over the range 0 .. ([classwords_per_codeword] - 1) while [partition_count]
+ is also less than [partitions_to_read] {
-
- 14) [vqclass] = array [classifications] element [j],([partition_count]+[classword_count])
- 15) [vqbook] = array [residue_books] element [vqclass],[pass]
- 16) if ([vqbook] is not 'unused') {
+ 12) iterate [j] over the range 0 .. [ch]-1 {
- 17) decode partition into output vector number [j], starting at scalar
+ 13) if vector [j] is not marked 'do not decode' {
+
+ 14) [vqclass] = array [classifications] element [j],[partition_count]
+ 15) [vqbook] = array [residue_books] element [vqclass],[pass]
+ 16) if ([vqbook] is not 'unused') {
+
+ 17) decode partition into output vector number [j], starting at scalar
offset [residue_begin]+[partition_count]*[residue_partition_size] using
codebook number [vqbook] in VQ context
}
- }
+ }
+
+ 18) increment [partition_count] by one
}
-
- 18) increment [classword_count]
- 19) increment [partition_count]
- 20) if ([classword_count] is less than [classvals_per_codeword]) AND
- ([partition_count] is less than [partitions_to_read) then continue at step 11
- 21) if ([partition_count] is less than [partitions_to_read) then continue at step 4
- }
+ }
- 22) done
+ 19) done
</programlisting>
<section><title>format 2 specifics</title>
<para>
-Format 2 is reducible to format 1 through the following steps, performed in order:
+Format 2 is reducible to format 1. It may be implemented as an additional stepprior to and an additional post-decode step after a normal format 1 decode.
+</para>
+
+<para>
+Format 2 handles 'do not decode' vectors differently than residue 0 or
+1; if all vectors are marked 'do not decode', no decode occurrs.
+However, if at least one vector is to be decoded, all the vectors are
+decoded. We then request normal format 1 to decode a single vector
+representing all output channels, rather than a vector for each
+channel. After decode, deinterleave the vector into independent vectors, one for each output channel. That is:</para>
<orderedlist>
- <listitem><simpara>Assume format 2 is to decode <emphasis>ch</emphasis> vectors of length <emphasis>n</emphasis>.</simpara></listitem>
- <listitem><simpara>Decode, using format 1, a single vector <varname>[v]</varname>of length <emphasis>ch</emphasis>*<emphasis>n</emphasis>.</simpara></listitem>
- <listitem><para>Deinterleave this single vector <varname>[v]</varname> into <emphasis>ch</emphasis> independent vectors according to:
+ <listitem><simpara>If all vectors 0 through <emphasis>ch</emphasis>-1 are marked 'do not decode', allocate and clear a single vector <varname>[v]</varname>of length <emphasis>ch*n</emphasis> and skip step 2 below; proceed directly to the post-decode step.</simpara></listitem>
+ <listitem><simpara>Rather than performing format 1 decode to produce <emphasis>ch</emphasis> vectors of length <emphasis>n</emphasis> each, call format 1 decode to produce a single vector <varname>[v]</varname> of length <emphasis>ch*n</emphasis>. </simpara></listitem>
+ <listitem><para>Post decode: Deinterleave the single vector <varname>[v]</varname> returned by format 1 decode as described above into <emphasis>ch</emphasis> independent vectors, one for each outputchannel, according to:
<programlisting>
1) iterate [i] over the range 0 ... [n]-1 {
2) iterate [j] over the range 0 ... [ch]-1 {
- 3) output vector number [j] element [i] = vector [t] element ([i] * [ch] +[j])
+ 3) output vector number [j] element [i] = vector [v] element ([i] * [ch] + [j])
}
}
</programlisting>
</para></listitem>
</orderedlist>
-</para>
-
-<para>
-Format 2 handles 'do not decode' vectors differently that residue 0 or
-1; if all vectors are marked 'do not decode', no decode occurrs.
-However, if at least one vector is to be decoded, all the vectors are
-decoded.</para>
</section>
</section>
</section>
+
projects / platform / upstream / libvorbis.git / blobdiff