Implement basic version of the SSS pattern for C++ target

An interesting extension of the AA pattern.  The main advantage of this is
that updating pointers in a control structure is  much more elegant than
duplicating all function implementations as is required by the normal AA
pattern. For more details see [1].

Only works for the SOA layout.

On a pure memory access level this pattern is equivalent to the AA pattern.
The difference is how the memory locations are calculated (by pointer swap
& shift or by different indexing functions for odd and even time steps).

[1]: "An auto-vectorization friendly parallel lattice Boltzmann streaming
      scheme for direct addressing" by Mohrhard et al. (2019)

1 files changed, 15 insertions, 0 deletions

diff --git a/boltzgen/kernel/template/update_sss_control_structure.cpp.mako b/boltzgen/kernel/template/update_sss_control_structure.cpp.mako
new file mode 100644
index 0000000..9197022
--- /dev/null
+++ b/boltzgen/kernel/template/update_sss_control_structure.cpp.mako
@@ -0,0 +1,15 @@
+<%
+if streaming != 'SSS':
+    raise Exception('"update_sss_control_structure" function only makes sense for the SSS pattern')
+%>
+void update_sss_control_structure(${float_type}** f) {
+% for i, c_i in enumerate(descriptor.c):
+    ${float_type}* f_old_${i} = f[${i}];
+% endfor
+% for i, c_i in enumerate(descriptor.c):
+    f[${i}]  = f_old_${descriptor.c.index(-c_i)};
+% endfor
+% for i, c_i in enumerate(descriptor.c):
+    f[${i}] += ${layout.neighbor_offset(-c_i)};
+% endfor
+}