What's all this JIT stuff

[d.healey]

I'm seeing this in the commits recently, is this related to C++ API or JS?

[Christoph Hart]

It's a big new feature that I am working on right now. Basically its a embedded C compiler that generates terribly fast machine code that can be used to write new DSP algorithms with almost native C++ speed. You can then call it from Javascript. This is the last missing piece to make the scripting environment really awesome

[d.healey]

Oh I see what you're doing. You're turning it up to 11!

[Christoph Hart]

Its about 95% faster than a Javascript loop so It's rather 11.5

[Christoph Hart]

Alright, I started to migrate this into HISE and it is real fun. I made some tests using a additive synthesizer with 6 harmonics and 6 low pass filters that smooth out the amplitudes.

Check out the CPU usage of the three different engines (native C++, NativeJIT and Javascript):

As you can see it's 17% JS vs 2,2% NativeJIT vs 0.9% C++. While it's not 100% there, it definitely allows writing DSP algorithms without compiling!

The Javascript Code

/** NativeJIT Example Script
*
*    Drop this into a ScriptFX Processor and compare the performance between the different engines.
*
*    The example algorithm is a additive sine wave generator with 6 sinewaves and simple LP smoothing
*    of the amplitudes to reduce clicking.
*
*    You can use the SliderPack to draw the harmonic structure and switch between the different engines
*    (they should sound the same)
*/

// Loads the "Example.cpp" file in the script folder and creates a NativeJIT compiler called "Example"
loadJITModule("Example.cpp");

// Compile and create an object from the given source code 
// The globals in the C code become local to this instance and you can access them via "c.global"
const var c = Example.createModule();

// Loads a compiled DSP module with the same functionality
const var cppMod = Libraries.load("core").createModule("additive_synth");

// The variables for the Javascript version
reg b = Buffer.create(6);
reg lastValues = Buffer.create(6);
reg uptime = 0.0;
reg uptimeDelta = 0.03;
reg a = 0.999;
reg invA = 1.0 - a;

// GUI Stuff...

const var SliderPack = Content.addSliderPack("SliderPack", 10, 10);
// [JSON SliderPack]
Content.setPropertiesFromJSON("SliderPack", {
  "width": 240,
  "sliderAmount": 6
});
// [/JSON SliderPack]
const var Engine = Content.addComboBox("Engine", 271, 9);
// [JSON Engine]
Content.setPropertiesFromJSON("Engine", {
  "items": "Off\nJavascript\nNativeJIT\nCompiled C++"
});
// [/JSON Engine]
Content.setHeight(120);

function prepareToPlay(sampleRate, blockSize)
{
    // Needed for DSP Modules...
    cppMod.prepareToPlay(sampleRate, blockSize);
    
}

function processBlock(channels)
{
    local e = Engine.getValue();
    
    if(e == 3)
    {
        // Calling the c.processBlock method iterates the buffer
        // and calls the defined process(float input) function for
        // each sample
        c.processBlock(channels[0]);
        
        channels[0] >> channels[1];
    }
    else if (e == 2)
    {
        // The same code in slow Javascript
        local a0, a1, a2, a3, a4, a5;
        local v0, v1, v2, v3, v4, v5;

        for(s in channels[0])
        {
            a0 = (lastValues[0]*a + b[0]*invA);
            a1 = (lastValues[1]*a + b[1]*invA);
            a2 = (lastValues[2]*a + b[2]*invA);
            a3 = (lastValues[3]*a + b[3]*invA);
            a4 = (lastValues[4]*a + b[4]*invA);
            a5 = (lastValues[5]*a + b[5]*i);
    
            v0 = a0 * Math.sin(uptime);
            v1 = a1 * Math.sin(2.0*uptime);
            v2 = a2 * Math.sin(3.0*uptime);
            v3 = a3 * Math.sin(4.0*uptime);
            v4 = a4 * Math.sin(5.0*uptime);
            v5 = a5 * Math.sin(6.0*uptime);
    
            lastValues[0] = a0;
            lastValues[1] = a1;
            lastValues[2] = a2;
            lastValues[3] = a3;
            lastValues[4] = a4;
            lastValues[5] = a5;

            uptime += uptimeDelta;

            s = v0+v1+v2+v3+v4+v5;
        }
        
        channels[0] >> channels[1];
        
    }
    else if (e == 4)
    {
        // give the native C++ module the buffer to calculate
        cppMod.processBlock(channels);
    }
}

function onControl(number, value)
{
    if(number == SliderPack)
    {
        // Set global values of NativeJIT modules directly
        // as if they were a Javascript Object!
        c.b[value] = SliderPack.getSliderValueAt(value);
        
        // Use the parameter API to set the overtones
        cppMod.setParameter(value, SliderPack.getSliderValueAt(value));
        
        // set the buffer value for the given overtone for JS
        b[value] = SliderPack.getSliderValueAt(value);
    }
}

The NativeJIT code

This is how the NativeJIT code looks like. It's plain old C with the addition of the Buffer type.

/** The NativeJIT code for the additive synthesiser. */

double uptime = 0.0;
double uptimeDelta = 0.03;

// Buffer is a custom type which correlates to the Buffer type in Javascript
// Treat them like a float array (there is a buffer overrun protection)
Buffer b(6);
Buffer lastValues(6);

float a = 0.999f;
float invA = 0.001f;

float process(float input)
{
    const float uptimeFloat = (float)uptime;

    const float a0 = (lastValues[0]*a + b[0]*invA);
    const float a1 = (lastValues[1]*a + b[1]*invA);
    const float a2 = (lastValues[2]*a + b[2]*invA);
    const float a3 = (lastValues[3]*a + b[3]*invA);
    const float a4 = (lastValues[4]*a + b[4]*invA);
    const float a5 = (lastValues[5]*a + b[5]*invA);

    const float v0 = a0 * sinf(uptimeFloat);
    const float v1 = a1 * sinf(2.0f*uptimeFloat);
    const float v2 = a2 * sinf(3.0f*uptimeFloat);
    const float v3 = a3 * sinf(4.0f*uptimeFloat);
    const float v4 = a4 * sinf(5.0f*uptimeFloat);
    const float v5 = a5 * sinf(6.0f*uptimeFloat);
    
    lastValues[0] = a0;
    lastValues[1] = a1;
    lastValues[2] = a2;
    lastValues[3] = a3;
    lastValues[4] = a4;
    lastValues[5] = a5;

    uptime += uptimeDelta;

    return v0+v1+v2+v3+v4+v5;
};

Note: This feature is not yet committed so you won't be able to check this out (I remove this hint when it's in the codebase).

[d.healey]

Looks exciting, I'm going to have to relearn C so what sort of things will this be useful for?

[Christoph Hart]

You can use this to script custom modulators, effects or synths. It's a bit like Reapers JSFX but embedded into HISE (I have to make performance tests between those two).

Especially the effect section in HISE is a bit underpopulated so this might come in handy there.

I will be using it to prototype DSP modules which will then be hardcoded into HISE. There are yet some drawbacks (only x64 support, no "real" branching, no iOS support)

[d.healey]

Aha now I get it!