Convert ONNX to the OneModel format · onemodel cookbook

Convert an ONNX file to OneModel’s own format once, load it with the same call, and get bit-identical outputs, with the weights read as memory-mapped views.

using RecursiveAI.OneModel;
using RecursiveAI.OneModel.Format;
 
ModelFormat.Convert("wide.onnx", "wide.onemodel");
Console.WriteLine($"wide.onnx      {new FileInfo("wide.onnx").Length,8:N0} bytes");
Console.WriteLine($"wide.onemodel  {new FileInfo("wide.onemodel").Length,8:N0} bytes");
Console.WriteLine($"OneModel format? {ModelFormat.IsModelFormatFile("wide.onemodel")}");
 
float[] input = Enumerable.Range(0, 256).Select(i => i / 256f).ToArray();
using var fromOnnx = Model.Load("wide.onnx");
using var fromOwn = Model.Load("wide.onemodel");
float[] a = fromOnnx.Run(input), b = fromOwn.Run(input);
 
bool same = a.Zip(b).All(p => BitConverter.SingleToInt32Bits(p.First) == BitConverter.SingleToInt32Bits(p.Second));
Console.WriteLine($"Bit-identical outputs: {same}");
 
File.WriteAllBytes("broken.onemodel", File.ReadAllBytes("wide.onemodel")[..4000]);
try { Model.Load("broken.onemodel"); }
catch (ModelFormatException e) { Console.WriteLine($"{e.Kind}: {e.Message}"); }

Text

wide.onnx       655,516 bytes
wide.onemodel   656,320 bytes
OneModel format? True
Bit-identical outputs: True
Malformed: the header says the file is 656320 bytes; it is 4000 (truncated or extended) (broken.onemodel at byte 48, file_length)

The format

A .onemodel file is a 64-byte header, a JSON manifest of the graph, and the raw weights, each tensor aligned to 64 bytes so it loads as a view of a memory map instead of being copied out of protobuf. What is saved is the imported graph before any optimization, so a converted model optimizes and runs exactly as the ONNX file it came from. The layout is in the OneModel format.

Model.Load and Session.Load tell the two kinds apart by their first eight bytes (ONEMODEL), so the loading code doesn’t change.
ModelFormat.Save(model, path) writes a model you already imported; ModelFormat.Load returns its IrModel.
A damaged file fails with ModelFormatException, whose Kind, Offset and FieldPath say what is wrong and where.

Good to know

The format is version 1 and unstable until OneModel 1.0: a version 1 file may stop loading in a later preview. Keep the ONNX file and convert again after you update.
On a model this small the file sizes are about the same. The gain is in loading: aligned weights are mapped, not parsed and copied.