Emscripten Uncaught RangeError: Source is too large, multiple Float32Arrays

Question

I'm trying to run a C++ function for 4x4 matrices multiplying. After 2 days it finally works, but not as expected.

Often parameters are being fed back to the function and then this line:

dataHeap2.set( new Uint8Array(data2.buffer) );

produces an error "Uncaught RangeError: Source is too large"

At a glance it looks like it's just a normal Float32Array with 16 elements, but after looking inside it's buffer size it seems to be different

console.log(data2.buffer.bufferLength);

The result are not expected 64 bytes but huge numbers like 3342345. Is this the problem? I found a workaround by manually copying values(like below), returning that and then the problem disappears. Unfortunately it makes my code much slower than operating directly on buffers.

// bad solution - which works
    for(var i = 0; i < 16; i++) {
        dataTarget[i] = result[i];
    }

Hopefully this night I'll find a better solution and I want to keep using this function as it's using a compiled C++ code using ASM.JS + SIMD for aninmating multiple characters. In pure JavaScript it's still too slow. Here's the entire function. I'm pretty sure that data2 is taking Emscripten's HEAP with it and I want to aviod it.

matrix4multiply = function(data, data2) {
    // Import function from Emscripten generated file
    var mmul_vec4 = Module.cwrap(
      'mmul_vec4', 'number', ['number', 'number', 'number']
    );

    var dataTarget = new Float32Array(16);

    // Get data byte size, allocate memory on Emscripten heap, and get pointer
    var nDataBytes = dataTarget.length * dataTarget.BYTES_PER_ELEMENT;

    // First matrix copy data to Emscripten heap
    var dataPtr = Module._malloc(nDataBytes);
    var dataPtr2 = Module._malloc(nDataBytes);
    var dataPtr3 = Module._malloc(nDataBytes);

    var dataHeap = new Uint8Array(Module.HEAPU8.buffer, dataPtr, nDataBytes);
    dataHeap.set( new Uint8Array(data.buffer) );

    // second matrix allocate and copy to emscripten's heap
    var dataHeap2 = new Uint8Array(Module.HEAPU8.buffer, dataPtr2, nDataBytes);
    dataHeap2.set( new Uint8Array(data2.buffer) );

    // target heap
    var targetHeap = new Uint8Array(Module.HEAPU8.buffer, dataPtr3, nDataBytes);
    targetHeap.set( new Uint8Array(dataTarget.buffer) );

    // Call the function by passing a number pointing to the byte location of 
    // the array of pointers on the Emscripten heap.  Emscripten knows what to do!
    mmul_vec4(dataHeap.byteOffset, dataHeap2.byteOffset, targetHeap.byteOffset);

    // get result
    var result = new Float32Array(targetHeap.buffer, targetHeap.byteOffset, 16);

    // bad solution - which works
    //for(var i = 0; i < 16; i++) {
    //    dataTarget[i] = result[i];
    //}

    // Free memory
    Module._free(dataHeap.byteOffset);
    Module._free(dataHeap2.byteOffset);
    Module._free(targetHeap.byteOffset);

    return result;
}

Edit: simplified version don't worry about malloc etc

    new Uint8Array(Module.HEAPU8.buffer, this.dataPtr, 64).set( new Uint8Array(data.buffer, data.byteOffset, 64) );

    // second matrix allocate and copy to emscripten's heap
    new Uint8Array(Module.HEAPU8.buffer, this.dataPtr + 72, 64).set( new Uint8Array(data2.buffer, data2.byteOffset, 64) );

    // multiply first two parameters and return in the last one 
    this.mmul_vec4(this.dataPtr, this.dataPtr + 72, this.dataPtr + 144);

    // like that it works, unfotunately copying is being made here
    return new Float32Array(Module.HEAPU8.buffer.slice(this.dataPtr + 144, this.dataPtr + 208));
    // with this version (if uncommented) there's just white screen(but it looks like the game is working.
    //return new Float32Array(Module.HEAPU8.buffer, this.dataPtr + 144, 16);

Answer 1

To use head 64 bytes of data2, specify offset and length.

dataHeap2.set( new Uint8Array(data2.buffer, data2.byteOffset, nDataBytes) );