Hi,
I want to call a C function dealing with arrays from Javascript.
The function is created with emscripten. I also want to create JS
functions handling native JavaScript arrays, for example a
Uint8Array.
>From my understanding I have to create a JS wrapper allocating an
array in the heap, copy the data from the JS array, process the data
through the emscripten generated function, and finally copy the
processed data back to a JS array.
Consider this example:
C function:
void multiply_array(uint8_t factor, uint8_t *buf, size_t buf_size)
{
for (int i = 0; i < buf_size; i++) {
buf[i] = factor * buf[i];
}
}
JS wrapper:
multiply_by_factor = function(u8array, factor) {
// need to get the array pointer, u8array is Uint8Array
// Get data byte size, allocate memory on Emscripten heap, and get pointer
var dataPtr = Module._malloc(u8array.length);
// allocate new Uint8Array in the Emscripten heap (directly accessed from
Module.HEAPU8)
var dataHeap = new Uint8Array(Module.HEAPU8.buffer, dataPtr, u8array.length);
// copy data to the heap
dataHeap.set(u8array);
// Call function and process data inplace
_multiply_array(factor, dataPtr, u8array.length);
var result = new Uint8Array(u8array.length);
result.set(dataHeap);
// Free memory from emscripten heap
Module._free(dataHeap.byteOffset);
return result;
}
This function is working fine, but I wonder if it's possible to avoid
to allocate data on the emscripten heap, in order to avoid the two
memcpy calls.
TIA
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