From 6e6624e5f90565e6b022f26fca1f32c5b28abed9 Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Tue, 23 Jul 2019 23:20:24 +0200
Subject: Generate basic example in plain C++
An attempt to produce a minimal LBM implementation to benchmark various
memory and vectorization schemes on the CPU.
---
standalone_cpp_codegen.py | 32 ++++++++++++++
template/standalone.mako | 109 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 141 insertions(+)
create mode 100644 standalone_cpp_codegen.py
create mode 100644 template/standalone.mako
diff --git a/standalone_cpp_codegen.py b/standalone_cpp_codegen.py
new file mode 100644
index 0000000..b38898a
--- /dev/null
+++ b/standalone_cpp_codegen.py
@@ -0,0 +1,32 @@
+import sympy
+from mako.template import Template
+from pathlib import Path
+
+from simulation import Geometry
+from symbolic.generator import LBM
+
+import symbolic.D2Q9 as D2Q9
+
+lbm = LBM(D2Q9)
+
+moments = lbm.moments(optimize = False)
+collide = lbm.bgk(f_eq = lbm.equilibrium(), tau = 0.6)
+
+geometry = Geometry(512, 512)
+
+program_src = Template(filename = str(Path(__file__).parent/'template/standalone.mako')).render(
+ descriptor = lbm.descriptor,
+ geometry = geometry,
+
+ steps = 100,
+
+ moments_subexpr = moments[0],
+ moments_assignment = moments[1],
+ collide_subexpr = collide[0],
+ collide_assignment = collide[1],
+
+ float_type = 'double',
+ ccode = sympy.ccode
+)
+
+print(program_src)
diff --git a/template/standalone.mako b/template/standalone.mako
new file mode 100644
index 0000000..6750de9
--- /dev/null
+++ b/template/standalone.mako
@@ -0,0 +1,109 @@
+#include <array>
+#include <cstdint>
+#include <memory>
+
+<%
+def pop_offset(i):
+ return i * geometry.volume
+%>
+
+void equilibrilize(${float_type}* f_next,
+ ${float_type}* f_prev,
+ const std::size_t gid)
+{
+ ${float_type}* preshifted_f_next = f_next + gid;
+ ${float_type}* preshifted_f_prev = f_prev + gid;
+
+% for i, w_i in enumerate(descriptor.w):
+ preshifted_f_next[${pop_offset(i)}] = ${w_i}.f;
+ preshifted_f_prev[${pop_offset(i)}] = ${w_i}.f;
+% endfor
+}
+
+<%
+def neighbor_offset(c_i):
+ return {
+ 2: lambda: c_i[1]*geometry.size_x + c_i[0],
+ 3: lambda: c_i[2]*geometry.size_x*geometry.size_y + c_i[1]*geometry.size_x + c_i[0]
+ }.get(descriptor.d)()
+
+%>
+
+void collide_and_stream( ${float_type}* f_next,
+ const ${float_type}* f_prev,
+ const int* material,
+ const std::size_t gid)
+{
+ const int m = material[gid];
+
+ if ( m == 0 ) {
+ return;
+ }
+
+ ${float_type}* preshifted_f_next = f_next + gid;
+ const ${float_type}* preshifted_f_prev = f_prev + gid;
+
+% for i, c_i in enumerate(descriptor.c):
+ const ${float_type} f_curr_${i} = preshifted_f_prev[${pop_offset(i) + neighbor_offset(-c_i)}];
+% endfor
+
+% for i, expr in enumerate(moments_subexpr):
+ const ${float_type} ${expr[0]} = ${ccode(expr[1])};
+% endfor
+
+% for i, expr in enumerate(moments_assignment):
+ ${float_type} ${ccode(expr)}
+% endfor
+
+% for i, expr in enumerate(collide_subexpr):
+ const ${float_type} ${expr[0]} = ${ccode(expr[1])};
+% endfor
+
+% for i, expr in enumerate(collide_assignment):
+ const ${float_type} ${ccode(expr)}
+% endfor
+
+% for i in range(0,descriptor.q):
+ preshifted_f_next[${pop_offset(i)}] = f_next_${i};
+% endfor
+}
+
+int main()
+{
+ auto f_a = std::make_unique<${float_type}[]>(${geometry.volume*descriptor.q});
+ auto f_b = std::make_unique<${float_type}[]>(${geometry.volume*descriptor.q});
+ auto material = std::make_unique<int[]>(${geometry.volume});
+
+ ${float_type}* f_prev = f_a.get();
+ ${float_type}* f_next = f_b.get();
+
+ for (int iX = 0; iX < ${geometry.size_x}; ++iX) {
+ for (int iY = 0; iY < ${geometry.size_x}; ++iY) {
+ if (iX == 0 || iY == 0 || iX == ${geometry.size_x-1} || iY == ${geometry.size_y-1}) {
+ material[iY*${geometry.size_x} + iX] = 0;
+ } else {
+ material[iY*${geometry.size_x} + iX] = 1;
+ }
+ }
+ }
+
+ for (std::size_t iCell = 0; iCell < ${geometry.volume}; ++iCell) {
+ equilibrilize(f_prev, f_next, iCell);
+ }
+
+ for (std::size_t iStep = 0; iStep < ${steps}; ++iStep) {
+ if (iStep % 2 == 0) {
+ f_next = f_a.get();
+ f_prev = f_b.get();
+ } else {
+ f_next = f_b.get();
+ f_prev = f_a.get();
+ }
+
+ for (std::size_t iCell = 0; iCell < ${geometry.volume}; ++iCell) {
+ collide_and_stream(f_next, f_prev, material.get(), iCell);
+ }
+ }
+
+ return 0;
+}
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