Accessors for unsigned 24-bit ints on Javascript DataViews

DataView_Uint24Accessors.js

/**
 * Provide a 24 bit int implementation for DataViews. Note this
 * causes two reads/writes per call, meaning it's going to be
 * around half as fast as the native implementations.
 */
DataView.prototype.getUint24 = function(pos) {
	return (this.getUint16(pos) << 8) + this.getUint8(pos+2);
}

DataView.prototype.setUint24 = function(pos, val) {
	this.setUint16(pos, val >> 8);
	this.setUint8(pos+2, val & ~4294967040); // this "magic number" masks off the first 16 bits
}

Unit test (for Mocha+Chai) is here: https://gist.github.com/nphyx/5895d07fba9686ac357f

Hi, @nphyx. This has been super helpful! I'm currently trying to add arbitrary 1-32 bit functionality to geotiff.js (geotiff on npm). I was wondering if getUint24 is for little endian or big endian? And if it's one of those, do you know what it would look like if there's another type of endian?

Thank you very much and have a great day. :-)

Would this be correct to cater for both little-endian and big-endian?

DataView.prototype.getUint24 = function(byteOffset=0, littleEndian=false) {
    return littleEndian
        ? this.getUint8(byteOffset) + (this.getUint16(byteOffset+1) << 8, true)
        : (this.getUint16(byteOffset) << 8) + this.getUint8(byteOffset+2);
}

That looks correct but it's been a while since I've messed with dataviews so I'm a little rusty. Can you confirm that it works?

It's working fine for big-endian (once defaults are included) – I've not been able to test little-endian I'm afraid, I just thought I'd offer it out :)