Testbenches for multiple outputs

[sei-jgwohlbier]

I have a network with multiple return values. I found that the testbench was not printing the imported predictions in the way that I expected. The reason was this generated code in myproject_test.cpp

 std::cout << "Predictions" << std::endl;
                // hls-fpga-machine-learning insert predictions                 
                for(int i = 0; i < N_LAYER_36; i++) {
                  std::cout << pr[i] << " ";
                }
                std::cout << std::endl;
                for(int i = 0; i < N_LAYER_37; i++) {
                  std::cout << pr[i] << " ";
                }

where I needed it to be

 std::cout << "Predictions" << std::endl;
                // hls-fpga-machine-learning insert predictions                 
                for(int i = 0; i < N_LAYER_36; i++) {
                  std::cout << pr[i] << " ";
                }
                std::cout << std::endl;
                for(int i = N_LAYER_36; i < N_LAYER_36 + N_LAYER_37; i++) {
                  std::cout << pr[i] << " ";
                }

I ginned up this hack

diff --git a/hls4ml/writer/vivado_writer.py b/hls4ml/writer/vivado_writer.py
index 5ab13736..7089d9f1 100644
--- a/hls4ml/writer/vivado_writer.py
+++ b/hls4ml/writer/vivado_writer.py
@@ -560,11 +560,16 @@ class VivadoWriter(Writer):
 
             elif '// hls-fpga-machine-learning insert predictions' in line:
                 newline = line
+                prev_size = "0"
                 for out in model_outputs:
-                    newline += indent + f'for(int i = 0; i < {out.size_cpp()}; i++) {{\n'
+                    newline += indent + f'for(int i = {prev_size}; i < {prev_size} + {out.size_cpp()}; i++) {{\n'
                     newline += indent + '  std::cout << pr[i] << " ";\n'
                     newline += indent + '}\n'
                     newline += indent + 'std::cout << std::endl;\n'
+                    if prev_size == "0":
+                        prev_size = f"{out.size_cpp()}"
+                    else:
+                        prev_size += f" + {out.size_cpp()}"
 
             elif '// hls-fpga-machine-learning insert tb-output' in line:
                 newline = line

and now I get this, which is close enough for the moment.

 std::cout << "Predictions" << std::endl;
                // hls-fpga-machine-learning insert predictions                 
                for(int i = 0; i < 0 + N_LAYER_36; i++) {
                  std::cout << pr[i] << " ";
                }
                std::cout << std::endl;
                for(int i = N_LAYER_36; i < N_LAYER_36 + N_LAYER_37; i++) {
                  std::cout << pr[i] << " ";
                }

Just putting it here in case anyone else runs into this. I didn't think I had enough for a bug report or a PR.