在 CPU 上助力实现实时 ML 推理

0:01 - Create the graph

// Get the path to the mlmodelc.
        NSBundle *main = [NSBundle mainBundle];
        NSString *mlmodelc_path = [main pathForResource:@"bitcrusher"
                                                 ofType:@"mlmodelc"];
        
        // Specify single-threaded execution.
        bnns_graph_compile_options_t options = BNNSGraphCompileOptionsMakeDefault();
        BNNSGraphCompileOptionsSetTargetSingleThread(options, true);
        
        // Compile the BNNSGraph.
        bnns_graph_t graph = BNNSGraphCompileFromFile(mlmodelc_path.UTF8String,
                                                      NULL, options);
        assert(graph.data);
        BNNSGraphCompileOptionsDestroy(options);

0:02 - Create context and workspace

// Create the context.
        context = BNNSGraphContextMake(graph);
        assert(context.data);
        
        // Set the argument type.
        BNNSGraphContextSetArgumentType(context, BNNSGraphArgumentTypePointer);
        
        // Specify the dynamic shape.
        uint64_t shape[] = {mMaxFramesToRender, 1, 1};
        bnns_graph_shape_t shapes[] = {
            (bnns_graph_shape_t) {.rank = 3, .shape = shape},
            (bnns_graph_shape_t) {.rank = 3, .shape = shape}
        };
        BNNSGraphContextSetDynamicShapes(context, NULL, 2, shapes);
        
        // Create the workspace.
        workspace_size = BNNSGraphContextGetWorkspaceSize(context, NULL) + NSPageSize();
        workspace = (char *)aligned_alloc(NSPageSize(), workspace_size);

0:03 - Calculate indices

// Calculate indices into the arguments array.
        dst_index = BNNSGraphGetArgumentPosition(graph, NULL, "dst");
        src_index = BNNSGraphGetArgumentPosition(graph, NULL, "src");
        resolution_index = BNNSGraphGetArgumentPosition(graph, NULL, "resolution");
        saturationGain_index = BNNSGraphGetArgumentPosition(graph, NULL, "saturationGain");
        dryWet_index = BNNSGraphGetArgumentPosition(graph, NULL, "dryWet");

0:04 - Execute graph

// Set the size of the first dimension.
            BNNSGraphContextSetBatchSize(context, NULL, frameCount);
            
            // Specify the direct pointer to the output buffer.
            arguments[dst_index] = {
                .data_ptr = outputBuffers[channel],
                .data_ptr_size = frameCount * sizeof(outputBuffers[channel][0])
            };
            
            // Specify the direct pointer to the input buffer.
            arguments[src_index] = {
                .data_ptr = (float *)inputBuffers[channel],
                .data_ptr_size = frameCount * sizeof(inputBuffers[channel][0])
            };
            
            // Specify the direct pointer to the resolution scalar parameter.
            arguments[resolution_index] = {
                .data_ptr = &mResolution,
                .data_ptr_size = sizeof(float)
            };
            
            // Specify the direct pointer to the saturation gain scalar parameter.
            arguments[saturationGain_index] = {
                .data_ptr = &mSaturationGain,
                .data_ptr_size = sizeof(float)
            };
            
            // Specify the direct pointer to the mix scalar parameter.
            arguments[dryWet_index] = {
                .data_ptr = &mMix,
                .data_ptr_size = sizeof(float)
            };
            
            // Execute the function.
            BNNSGraphContextExecute(context, NULL,
                                    5, arguments,
                                    workspace_size, workspace);

0:05 - Declare buffers

// Create source buffer that represents a pure sine wave.
    let srcChartData: UnsafeMutableBufferPointer<Float> = {
        let buffer = UnsafeMutableBufferPointer<Float>.allocate(capacity: sampleCount)
        
        for i in 0 ..< sampleCount {
            buffer[i] = sin(Float(i) / ( Float(sampleCount) / .pi) * 4)
        }
        
        return buffer
    }()
    
    // Create destination buffer.
    let dstChartData = UnsafeMutableBufferPointer<Float>.allocate(capacity: sampleCount)
    
    // Create scalar parameter buffer for resolution.
    let resolutionValue = UnsafeMutableBufferPointer<Float>.allocate(capacity: 1)
    
    // Create scalar parameter buffer for resolution.
    let saturationGainValue = UnsafeMutableBufferPointer<Float>.allocate(capacity: 1)
    
    // Create scalar parameter buffer for resolution.
    let mixValue = UnsafeMutableBufferPointer<Float>.allocate(capacity: 1)

0:06 - Declare indices

// Declare BNNSGraph objects.
    let graph: bnns_graph_t
    let context: bnns_graph_context_t
    
    // Declare workspace.
    let workspace: UnsafeMutableRawBufferPointer
    
    // Create the indices into the arguments array.
    let dstIndex: Int
    let srcIndex: Int
    let resolutionIndex: Int
    let saturationGainIndex: Int
    let dryWetIndex: Int

0:07 - Create graph and context

// Get the path to the mlmodelc.
        guard let fileName = Bundle.main.url(
            forResource: "bitcrusher",
            withExtension: "mlmodelc")?.path() else {
            fatalError("Unable to load model.")
        }
        
        // Compile the BNNSGraph.
        graph = BNNSGraphCompileFromFile(fileName, nil,
                                         BNNSGraphCompileOptionsMakeDefault())
        
        // Create the context.
        context = BNNSGraphContextMake(graph)
        
        // Verify graph and context.
        guard graph.data != nil && context.data != nil else { fatalError()}

0:08 - Finish initialization

// Set the argument type.
        BNNSGraphContextSetArgumentType(context, BNNSGraphArgumentTypePointer)
        
        // Set the size of the first dimension.
        BNNSGraphContextSetBatchSize(context, nil, UInt64(sampleCount))
        
        // Create the workspace.
        workspace = .allocate(byteCount: BNNSGraphContextGetWorkspaceSize(context, nil),
                              alignment: NSPageSize())
        
        // Calculate indices into the arguments array.
        dstIndex = BNNSGraphGetArgumentPosition(graph, nil, "dst")
        srcIndex = BNNSGraphGetArgumentPosition(graph, nil, "src")
        resolutionIndex = BNNSGraphGetArgumentPosition(graph, nil, "resolution")
        saturationGainIndex = BNNSGraphGetArgumentPosition(graph, nil, "saturationGain")
        dryWetIndex = BNNSGraphGetArgumentPosition(graph, nil, "dryWet")

0:09 - Create arguments array

// Copy slider values to scalar parameter buffers.
        resolutionValue.initialize(repeating: resolution.value)
        saturationGainValue.initialize(repeating: saturationGain.value)
        mixValue.initialize(repeating: mix.value)
        
        // Specify output and input arguments.
        var arguments = [(dstChartData, dstIndex),
                         (srcChartData, srcIndex),
                         (resolutionValue, resolutionIndex),
                         (saturationGainValue, saturationGainIndex),
                         (mixValue, dryWetIndex)]
            .sorted { a, b in
                a.1 < b.1
            }
            .map {
                var argument = bnns_graph_argument_t()
                
                argument.data_ptr = UnsafeMutableRawPointer(mutating: $0.0.baseAddress!)
                argument.data_ptr_size = $0.0.count * MemoryLayout<Float>.stride
                
                return argument
            }

0:10 - Execute graph

// Execute the function.
        BNNSGraphContextExecute(context,
                                nil,
                                arguments.count, &arguments,