runmat-runtime 0.6.0

Core runtime for RunMat with builtins, BLAS/LAPACK integration, and execution APIs
Documentation
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
use runmat_builtins::{ObjectInstance, Tensor, Value};
use runmat_macros::runtime_builtin;
use std::collections::BTreeSet;
use std::path::PathBuf;

use crate::BuiltinResult;

use super::{
    any_type, deep_learning_error, gather_args, model, parse_name_values, scalar_text,
    unsupported_error,
};

const EXPORT_ONNX: &str = "exportONNXNetwork";
const DEFAULT_OPSET_VERSION: i64 = 14;
const MIN_SUPPORTED_OPSET_VERSION: i64 = 13;
const MAX_SUPPORTED_OPSET_VERSION: i64 = 20;
const ONNX_DOUBLE: i32 = 11;

#[derive(Debug)]
struct ExportOptions {
    opset_version: i64,
    batch_size: Option<i64>,
    input_name: Option<String>,
    output_name: Option<String>,
}

impl Default for ExportOptions {
    fn default() -> Self {
        Self {
            opset_version: DEFAULT_OPSET_VERSION,
            batch_size: None,
            input_name: None,
            output_name: None,
        }
    }
}

#[derive(Debug)]
struct ExportGraph {
    nodes: Vec<Node>,
    initializers: Vec<Initializer>,
    input: ValueInfo,
    output: ValueInfo,
}

#[derive(Debug)]
struct Node {
    name: String,
    op_type: String,
    inputs: Vec<String>,
    outputs: Vec<String>,
    attributes: Vec<Attribute>,
}

#[derive(Debug)]
struct Initializer {
    name: String,
    dims: Vec<i64>,
    data: Vec<f64>,
}

#[derive(Debug)]
struct ValueInfo {
    name: String,
    batch_size: Option<i64>,
    features: i64,
}

#[derive(Debug)]
enum Attribute {
    Float { name: &'static str, value: f32 },
    Int { name: &'static str, value: i64 },
}

#[runtime_builtin(
    name = "exportONNXNetwork",
    category = "deep_learning",
    summary = "Export supported feed-forward deep-learning networks to ONNX.",
    keywords = "exportONNXNetwork,deep learning,onnx,export",
    type_resolver(any_type),
    descriptor(crate::builtins::deep_learning::OBJECT_DESCRIPTOR),
    builtin_path = "crate::builtins::deep_learning::onnx"
)]
pub(super) async fn export_onnx_network_builtin(args: Vec<Value>) -> BuiltinResult<Value> {
    if matches!(crate::output_count::current_output_count(), Some(n) if n > 0) {
        return Err(deep_learning_error(
            EXPORT_ONNX,
            "exportONNXNetwork does not return output arguments",
        ));
    }

    let args = gather_args(args).await?;
    if args.len() < 2 {
        return Err(deep_learning_error(
            EXPORT_ONNX,
            "exportONNXNetwork: expected network and filename",
        ));
    }
    let network = require_network_object(&args[0])?;
    let filename = scalar_text(&args[1], EXPORT_ONNX)?;
    let options = parse_export_options(&args[2..])?;
    let graph = build_export_graph(network, &options)?;
    let bytes = encode_model(&graph, options.opset_version);
    runmat_filesystem::write_async(PathBuf::from(&filename), &bytes)
        .await
        .map_err(|err| {
            deep_learning_error(
                EXPORT_ONNX,
                format!("exportONNXNetwork: failed to write '{filename}': {err}"),
            )
        })?;
    Ok(Value::OutputList(Vec::new()))
}

fn require_network_object(value: &Value) -> BuiltinResult<&ObjectInstance> {
    match value {
        Value::Object(object) if model::is_deep_learning_network_object(object) => Ok(object),
        other => Err(deep_learning_error(
            EXPORT_ONNX,
            format!(
                "exportONNXNetwork: expected a dlnetwork or trained network object, got {other:?}"
            ),
        )),
    }
}

fn parse_export_options(args: &[Value]) -> BuiltinResult<ExportOptions> {
    let map = parse_name_values(args.to_vec(), EXPORT_ONNX)?;
    let mut options = ExportOptions::default();
    for (key, value) in map {
        match key.as_str() {
            "opsetversion" => {
                let version = integer_scalar(&value, "OpsetVersion")?;
                if !(MIN_SUPPORTED_OPSET_VERSION..=MAX_SUPPORTED_OPSET_VERSION).contains(&version) {
                    return Err(deep_learning_error(
                        EXPORT_ONNX,
                        format!(
                            "exportONNXNetwork: OpsetVersion must be between {MIN_SUPPORTED_OPSET_VERSION} and {MAX_SUPPORTED_OPSET_VERSION}"
                        ),
                    ));
                }
                options.opset_version = version;
            }
            "batchsize" => {
                options.batch_size = Some(integer_scalar(&value, "BatchSize")?);
            }
            "inputnames" => {
                options.input_name = Some(single_name(&value, "InputNames")?);
            }
            "outputnames" => {
                options.output_name = Some(single_name(&value, "OutputNames")?);
            }
            "verbose" => {
                let _ = logical_scalar(&value, "Verbose")?;
            }
            other => {
                return Err(deep_learning_error(
                    EXPORT_ONNX,
                    format!("exportONNXNetwork: unsupported option '{other}'"),
                ));
            }
        }
    }
    Ok(options)
}

fn integer_scalar(value: &Value, label: &str) -> BuiltinResult<i64> {
    let n = super::numeric_scalar(value, EXPORT_ONNX, label)?;
    if n.fract().abs() > f64::EPSILON || n < 1.0 || n > i64::MAX as f64 {
        return Err(deep_learning_error(
            EXPORT_ONNX,
            format!("exportONNXNetwork: {label} must be a positive integer scalar"),
        ));
    }
    Ok(n as i64)
}

fn logical_scalar(value: &Value, label: &str) -> BuiltinResult<bool> {
    match value {
        Value::Bool(flag) => Ok(*flag),
        Value::Num(n) if *n == 0.0 || *n == 1.0 => Ok(*n != 0.0),
        Value::Tensor(t) if t.data.len() == 1 && (t.data[0] == 0.0 || t.data[0] == 1.0) => {
            Ok(t.data[0] != 0.0)
        }
        other => Err(deep_learning_error(
            EXPORT_ONNX,
            format!(
                "exportONNXNetwork: {label} must be logical scalar true or false, got {other:?}"
            ),
        )),
    }
}

fn single_name(value: &Value, label: &str) -> BuiltinResult<String> {
    let values = match value {
        Value::String(_) | Value::CharArray(_) => vec![scalar_text(value, EXPORT_ONNX)?],
        Value::StringArray(array) => array.data.clone(),
        Value::Cell(cell) => {
            let mut names = Vec::with_capacity(cell.data.len());
            for item in &cell.data {
                names.push(scalar_text(item, EXPORT_ONNX)?);
            }
            names
        }
        other => {
            return Err(deep_learning_error(
                EXPORT_ONNX,
                format!("exportONNXNetwork: {label} must be text, string array, or cell text, got {other:?}"),
            ));
        }
    };
    match values.as_slice() {
        [name] if !name.is_empty() => Ok(name.clone()),
        [_] => Err(deep_learning_error(
            EXPORT_ONNX,
            format!("exportONNXNetwork: {label} must not be empty"),
        )),
        _ => Err(deep_learning_error(
            EXPORT_ONNX,
            format!("exportONNXNetwork: this exporter supports exactly one {label} value"),
        )),
    }
}

fn build_export_graph(
    network: &ObjectInstance,
    options: &ExportOptions,
) -> BuiltinResult<ExportGraph> {
    let layers = network
        .properties
        .get("Layers")
        .cloned()
        .map(|value| model::layers_from_network_value(value, EXPORT_ONNX))
        .transpose()?
        .unwrap_or_default();
    model::validate_forward_layers(&layers, EXPORT_ONNX)?;
    if layers.is_empty() {
        return Err(deep_learning_error(
            EXPORT_ONNX,
            "exportONNXNetwork: network must contain at least one layer",
        ));
    }

    let layer_names = super::layer_names(&layers, EXPORT_ONNX)?;
    ensure_unique_layer_names(&layer_names)?;
    let input_name = options
        .input_name
        .clone()
        .or(network_name(network, "InputNames")?)
        .unwrap_or_else(|| layer_names[0].clone());
    let output_name = options
        .output_name
        .clone()
        .or(network_name(network, "OutputNames")?)
        .unwrap_or_else(|| "output".to_string());

    let mut nodes = Vec::new();
    let mut initializers = Vec::new();
    let mut current_tensor = input_name.clone();
    let mut current_features = None;
    let mut saw_input = false;

    for (idx, layer_value) in layers.iter().enumerate() {
        let Value::Object(layer) = layer_value else {
            return Err(deep_learning_error(
                EXPORT_ONNX,
                "exportONNXNetwork: network layers must be layer objects",
            ));
        };
        let layer_name = layer_names[idx].clone();
        match layer.class_name.as_str() {
            "nnet.cnn.layer.FeatureInputLayer" => {
                if idx != 0 {
                    return Err(deep_learning_error(
                        EXPORT_ONNX,
                        "exportONNXNetwork: featureInputLayer must be the first exported layer",
                    ));
                }
                current_features = Some(model::feature_input_width(layer, EXPORT_ONNX)? as i64);
                saw_input = true;
            }
            "nnet.cnn.layer.FullyConnectedLayer" => {
                let input_features = current_features.ok_or_else(|| {
                    deep_learning_error(
                        EXPORT_ONNX,
                        "exportONNXNetwork: fullyConnectedLayer requires a preceding featureInputLayer",
                    )
                })?;
                let weights = model::tensor_property(layer, "Weights", EXPORT_ONNX)?;
                if weights.shape.len() > 2 || weights.cols as i64 != input_features {
                    return Err(deep_learning_error(
                        EXPORT_ONNX,
                        format!(
                            "exportONNXNetwork: fullyConnectedLayer Weights must be outputSize-by-{input_features}"
                        ),
                    ));
                }
                let bias = model::tensor_property(layer, "Bias", EXPORT_ONNX)?;
                if bias.data.len() != weights.rows {
                    return Err(deep_learning_error(
                        EXPORT_ONNX,
                        format!(
                            "exportONNXNetwork: fullyConnectedLayer Bias must have {} elements",
                            weights.rows
                        ),
                    ));
                }
                let output_size =
                    model::positive_property_usize(layer, "OutputSize", EXPORT_ONNX)? as i64;
                if output_size as usize != weights.rows {
                    return Err(deep_learning_error(
                        EXPORT_ONNX,
                        "exportONNXNetwork: fullyConnectedLayer OutputSize must match Weights rows",
                    ));
                }
                let weight_name = format!("{layer_name}.Weights");
                let bias_name = format!("{layer_name}.Bias");
                initializers.push(Initializer {
                    name: weight_name.clone(),
                    dims: vec![weights.rows as i64, weights.cols as i64],
                    data: tensor_to_row_major_2d(&weights),
                });
                initializers.push(Initializer {
                    name: bias_name.clone(),
                    dims: vec![weights.rows as i64],
                    data: bias.data.clone(),
                });
                let next_tensor = format!("{layer_name}/Gemm");
                nodes.push(Node {
                    name: layer_name,
                    op_type: "Gemm".to_string(),
                    inputs: vec![current_tensor, weight_name, bias_name],
                    outputs: vec![next_tensor.clone()],
                    attributes: vec![Attribute::Int {
                        name: "transB",
                        value: 1,
                    }],
                });
                current_tensor = next_tensor;
                current_features = Some(output_size);
            }
            "nnet.cnn.layer.ReLULayer" => {
                let next_tensor = format!("{layer_name}/Relu");
                nodes.push(Node {
                    name: layer_name,
                    op_type: "Relu".to_string(),
                    inputs: vec![current_tensor],
                    outputs: vec![next_tensor.clone()],
                    attributes: vec![],
                });
                current_tensor = next_tensor;
            }
            "nnet.cnn.layer.ELULayer" => {
                let alpha = layer
                    .properties
                    .get("Alpha")
                    .map(|value| super::numeric_scalar(value, EXPORT_ONNX, "Alpha"))
                    .transpose()?
                    .unwrap_or(1.0);
                let next_tensor = format!("{layer_name}/Elu");
                nodes.push(Node {
                    name: layer_name,
                    op_type: "Elu".to_string(),
                    inputs: vec![current_tensor],
                    outputs: vec![next_tensor.clone()],
                    attributes: vec![Attribute::Float {
                        name: "alpha",
                        value: alpha as f32,
                    }],
                });
                current_tensor = next_tensor;
            }
            "nnet.cnn.layer.SoftmaxLayer" => {
                let next_tensor = format!("{layer_name}/Softmax");
                nodes.push(Node {
                    name: layer_name,
                    op_type: "Softmax".to_string(),
                    inputs: vec![current_tensor],
                    outputs: vec![next_tensor.clone()],
                    attributes: vec![Attribute::Int {
                        name: "axis",
                        value: 1,
                    }],
                });
                current_tensor = next_tensor;
            }
            "nnet.cnn.layer.ClassificationOutputLayer" | "nnet.cnn.layer.RegressionOutputLayer" => {
                if idx + 1 != layers.len() {
                    return Err(deep_learning_error(
                        EXPORT_ONNX,
                        "exportONNXNetwork: output layers must be terminal layers",
                    ));
                }
            }
            other => {
                return Err(unsupported_error(
                    EXPORT_ONNX,
                    format!("exportONNXNetwork: layer type '{other}' cannot be exported to ONNX"),
                ));
            }
        }
    }

    if !saw_input {
        return Err(deep_learning_error(
            EXPORT_ONNX,
            "exportONNXNetwork: network must start with a supported input layer",
        ));
    }
    let output_features = current_features.ok_or_else(|| {
        deep_learning_error(
            EXPORT_ONNX,
            "exportONNXNetwork: exported graph must produce a numeric feature tensor",
        )
    })?;
    if current_tensor != output_name {
        nodes.push(Node {
            name: "output".to_string(),
            op_type: "Identity".to_string(),
            inputs: vec![current_tensor],
            outputs: vec![output_name.clone()],
            attributes: vec![],
        });
    }

    Ok(ExportGraph {
        nodes,
        initializers,
        input: ValueInfo {
            name: input_name,
            batch_size: options.batch_size,
            features: feature_input_width_from_first_layer(&layers)?,
        },
        output: ValueInfo {
            name: output_name,
            batch_size: options.batch_size,
            features: output_features,
        },
    })
}

fn feature_input_width_from_first_layer(layers: &[Value]) -> BuiltinResult<i64> {
    let Some(Value::Object(layer)) = layers.first() else {
        return Err(deep_learning_error(
            EXPORT_ONNX,
            "exportONNXNetwork: network must start with a featureInputLayer",
        ));
    };
    if layer.class_name != "nnet.cnn.layer.FeatureInputLayer" {
        return Err(deep_learning_error(
            EXPORT_ONNX,
            "exportONNXNetwork: network must start with a featureInputLayer",
        ));
    }
    Ok(model::feature_input_width(layer, EXPORT_ONNX)? as i64)
}

fn ensure_unique_layer_names(names: &[String]) -> BuiltinResult<()> {
    let mut seen = BTreeSet::new();
    for name in names {
        if !seen.insert(name.clone()) {
            return Err(deep_learning_error(
                EXPORT_ONNX,
                format!("exportONNXNetwork: duplicate layer name '{name}'"),
            ));
        }
    }
    Ok(())
}

fn network_name(network: &ObjectInstance, property: &str) -> BuiltinResult<Option<String>> {
    let Some(value) = network.properties.get(property) else {
        return Ok(None);
    };
    match value {
        Value::StringArray(array) if array.data.is_empty() => Ok(None),
        Value::StringArray(array) if array.data.len() == 1 && !array.data[0].is_empty() => {
            Ok(Some(array.data[0].clone()))
        }
        Value::StringArray(_) => Err(deep_learning_error(
            EXPORT_ONNX,
            format!("exportONNXNetwork: network {property} metadata must contain exactly one non-empty name"),
        )),
        Value::String(name) if !name.is_empty() => Ok(Some(name.clone())),
        Value::String(_) => Ok(None),
        _ => Ok(None),
    }
}

fn tensor_to_row_major_2d(tensor: &Tensor) -> Vec<f64> {
    let rows = tensor.rows;
    let cols = tensor.cols;
    let mut out = Vec::with_capacity(rows * cols);
    for row in 0..rows {
        for col in 0..cols {
            out.push(tensor.data[row + col * rows]);
        }
    }
    out
}

fn encode_model(graph: &ExportGraph, opset_version: i64) -> Vec<u8> {
    let mut model = Vec::new();
    put_varint_field(&mut model, 1, 10);
    put_string_field(&mut model, 2, "runmat");
    put_string_field(&mut model, 3, env!("CARGO_PKG_VERSION"));
    put_varint_field(&mut model, 5, 1);
    put_message_field(&mut model, 7, &encode_graph(graph));
    put_message_field(&mut model, 8, &encode_opset("", opset_version));
    put_message_field(
        &mut model,
        14,
        &encode_string_pair("runmat.supported_execution", "sequential-feedforward"),
    );
    model
}

fn encode_graph(graph: &ExportGraph) -> Vec<u8> {
    let mut out = Vec::new();
    for node in &graph.nodes {
        put_message_field(&mut out, 1, &encode_node(node));
    }
    put_string_field(&mut out, 2, "RunMatExportedNetwork");
    for initializer in &graph.initializers {
        put_message_field(&mut out, 5, &encode_initializer(initializer));
    }
    put_message_field(&mut out, 11, &encode_value_info(&graph.input));
    put_message_field(&mut out, 12, &encode_value_info(&graph.output));
    out
}

fn encode_node(node: &Node) -> Vec<u8> {
    let mut out = Vec::new();
    for input in &node.inputs {
        put_string_field(&mut out, 1, input);
    }
    for output in &node.outputs {
        put_string_field(&mut out, 2, output);
    }
    put_string_field(&mut out, 3, &node.name);
    put_string_field(&mut out, 4, &node.op_type);
    for attr in &node.attributes {
        put_message_field(&mut out, 5, &encode_attribute(attr));
    }
    out
}

fn encode_attribute(attribute: &Attribute) -> Vec<u8> {
    let mut out = Vec::new();
    match attribute {
        Attribute::Float { name, value } => {
            put_string_field(&mut out, 1, name);
            put_fixed32_field(&mut out, 2, value.to_bits());
            put_varint_field(&mut out, 20, 1);
        }
        Attribute::Int { name, value } => {
            put_string_field(&mut out, 1, name);
            put_varint_field(&mut out, 3, *value as u64);
            put_varint_field(&mut out, 20, 2);
        }
    }
    out
}

fn encode_initializer(initializer: &Initializer) -> Vec<u8> {
    let mut out = Vec::new();
    for dim in &initializer.dims {
        put_varint_field(&mut out, 1, *dim as u64);
    }
    put_varint_field(&mut out, 2, ONNX_DOUBLE as u64);
    put_string_field(&mut out, 8, &initializer.name);
    let mut raw = Vec::with_capacity(initializer.data.len() * 8);
    for value in &initializer.data {
        raw.extend_from_slice(&value.to_le_bytes());
    }
    put_bytes_field(&mut out, 9, &raw);
    out
}

fn encode_value_info(info: &ValueInfo) -> Vec<u8> {
    let mut out = Vec::new();
    put_string_field(&mut out, 1, &info.name);
    put_message_field(&mut out, 2, &encode_type(info));
    out
}

fn encode_type(info: &ValueInfo) -> Vec<u8> {
    let mut tensor = Vec::new();
    put_varint_field(&mut tensor, 1, ONNX_DOUBLE as u64);
    put_message_field(&mut tensor, 2, &encode_shape(info));
    let mut out = Vec::new();
    put_message_field(&mut out, 1, &tensor);
    out
}

fn encode_shape(info: &ValueInfo) -> Vec<u8> {
    let mut out = Vec::new();
    put_message_field(
        &mut out,
        1,
        &encode_dimension(info.batch_size, Some("batch")),
    );
    put_message_field(&mut out, 1, &encode_dimension(Some(info.features), None));
    out
}

fn encode_dimension(value: Option<i64>, param: Option<&str>) -> Vec<u8> {
    let mut out = Vec::new();
    if let Some(value) = value {
        put_varint_field(&mut out, 1, value as u64);
    } else if let Some(param) = param {
        put_string_field(&mut out, 2, param);
    }
    out
}

fn encode_opset(domain: &str, version: i64) -> Vec<u8> {
    let mut out = Vec::new();
    if !domain.is_empty() {
        put_string_field(&mut out, 1, domain);
    }
    put_varint_field(&mut out, 2, version as u64);
    out
}

fn encode_string_pair(key: &str, value: &str) -> Vec<u8> {
    let mut out = Vec::new();
    put_string_field(&mut out, 1, key);
    put_string_field(&mut out, 2, value);
    out
}

fn put_string_field(out: &mut Vec<u8>, field: u32, value: &str) {
    put_bytes_field(out, field, value.as_bytes());
}

fn put_message_field(out: &mut Vec<u8>, field: u32, value: &[u8]) {
    put_bytes_field(out, field, value);
}

fn put_bytes_field(out: &mut Vec<u8>, field: u32, value: &[u8]) {
    put_key(out, field, 2);
    put_varint(out, value.len() as u64);
    out.extend_from_slice(value);
}

fn put_varint_field(out: &mut Vec<u8>, field: u32, value: u64) {
    put_key(out, field, 0);
    put_varint(out, value);
}

fn put_fixed32_field(out: &mut Vec<u8>, field: u32, value: u32) {
    put_key(out, field, 5);
    out.extend_from_slice(&value.to_le_bytes());
}

fn put_key(out: &mut Vec<u8>, field: u32, wire_type: u8) {
    put_varint(out, ((field as u64) << 3) | wire_type as u64);
}

fn put_varint(out: &mut Vec<u8>, mut value: u64) {
    while value >= 0x80 {
        out.push((value as u8 & 0x7f) | 0x80);
        value >>= 7;
    }
    out.push(value as u8);
}

#[cfg(test)]
mod tests {
    use super::*;

    fn has_length_delimited_field(bytes: &[u8], field: u32, payload: &[u8]) -> bool {
        let key = ((field as u64) << 3) | 2;
        let mut expected = Vec::new();
        put_varint(&mut expected, key);
        put_varint(&mut expected, payload.len() as u64);
        expected.extend_from_slice(payload);
        bytes
            .windows(expected.len())
            .any(|window| window == expected.as_slice())
    }

    #[test]
    fn initializer_name_uses_tensor_proto_name_field() {
        let initializer = Initializer {
            name: "fc.Weights".to_string(),
            dims: vec![2, 3],
            data: vec![1.0, 2.0, 3.0, 4.0, 5.0, 6.0],
        };
        let encoded = encode_initializer(&initializer);

        assert!(has_length_delimited_field(&encoded, 8, b"fc.Weights"));
        assert!(!has_length_delimited_field(&encoded, 4, b"fc.Weights"));
    }
}