EMSCRIPTEN, ASM.JSAND BILLIONS OF MATH OPS

Luka Zakrajšek

@bancek

Webcamp Ljubljana 2016

March 12, 2016

PROBLEMmusic transcription - from audio samples to music notes

⬇

ASM.JSan extraordinarily optimizable, low-level subset of JavaScript

"Assembler for Web"

EMSCRIPTENLLVM-based project that compiles C and C++ into highly-

optimizable JavaScript in asm.js format

It lets you run C and C++ on the web at near-native speed,without plugins.

C CODE#include<stdio.h>

int main() { printf("hello, world!\n"); return 0; }

COMPILE$ emcc hello_world.c

And run:$ node a.out.js hello, world!

C LIBRARY EXAMPLE

var samplesData = Module._malloc(samples.length * 8); var outJson = Module._malloc(4); var outJsonSize = Module._malloc(4);

Module.HEAPF64.set(samples, samplesData / 8); Module.ccall('samplesToTtm', 'number', ['number', 'number', 'number', 'number', [samplesData, samplesCount, sampleRate, layer, outJson, outJsonSize]); Module._free(samplesData);

var jsonSize = Module.getValue(outJsonSize, 'i32'); var jsonPtr = Module.getValue(outJson, 'i32'); var jsonBytes = Module.HEAPU8.subarray(jsonPtr, jsonPtr + jsonSize); var json = new TextDecoder('utf-8').decode(jsonBytes);

JSON.parse(json);

SOME NUMBERS180s × 41 000 samples per second = 7 380 000 samples

3 600 hops × 345 buckets × 4 410 samples × 2 =

10 954 440 000 multiplications

RESULTS

DEMO