sam henri goldhey wanna see something kinda interesting? this was the entire fix to the iPhone Antennagate in 2010. 20 bytes.
(this is going to be a very long thread 🧵)
For context, back in 2010 when the iPhone 4 came out, people noticed you could grip the phone in a certain way and the signal bars would plummet from 5 to, like, 2.
A few weeks later, they published a letter (https://www.apple.com/newsroom/2010/07/02Letter-from-Apple-Regarding-iPhone-4/) admitting fault, blaming a bad formula.
The letter was shared around and clowned upon (https://daringfireball.net/2010/07/translation_iphone_4) but nobody really looked into what the formula between 4.0 and the patch in 4.0.1
I was a stupid eight-year-old at the time, but now I’m a stupid adult with access to a disassembler.
I downloaded both firmwares and started poking around. In the CoreTelephony framework, I found a promising looking binary: CommCenter. Looking at the strings gave me a pretty good sense that this is where the bar formula was.
The actual calculation is dead simple. When converting signal strength to bars, CommCenter loads each threshold from memory and compares until it finds the right range.
This code is not the problem...
...this is. This is the lookup table. When you convert the bytes to actual dBm values, you get:
-115, -111, -107, -103, and -99
(the closer to zero, the better the signal)
For example, here you need -107 or better signal to see 3 bars.
When you plot this onto a chart, you can see how the values are kinda screwed up since the values are really optimistic. Most of the time, you would see 4-5 bars. But when you gripped it, since the falloff is so sharp, you’d see a catastrophic drop from 5 to 2 bars.
In 4.0.1, they changed these values to be way smoother. Mapped onto a chart, you can see that it takes a lot to drop from 5 to 0 bars. It’s harder to see 5 bars, but it’s harder to plummet bars.
So there ya go. 20 bytes.
This has concluded a Tech Thread. Back to shitposting.
joey 💙@samhenrigold I’d heard about the antenna issue but never looked into it. So if I understand you correctly the issue was strictly the perception of signal based on the bars shown, and not the actual signal itself?
@joey It was probably both, the fact that they did a significant reworking of the antenna in the next model is damning
Bob K Mertz 
@samhenrigold
This really strikes me as being the difference between a linear and nonlinear gas gauge in a car. If you have a linear gas gauge it really *feels* like you are using gas faster because most cars are nonlinear and stay at the full mark much longer and fall more rapidly as your tank gets lower.
In this case holding the cell phone a certain way *does* weaken signal but not as drastically as the display was showing.
But despite what the display makes you *feel* the reality is that your car will run out of gas at some point and you body will affect signal strength to some extent even if it now *feels* like it doesn't.
@joey