4 ms·

PAR files use ReedSolomon error correction which IMO might as well be magic. Galois Fields are really awesome (and are related to CRC codes). The level of effo

PAR files use ReedSolomon error correction which IMO might as well be magic. Galois Fields are really awesome (and are related to CRC codes). The level of effort to learn is quite high. NASAs guide to ReedSolomon was amazing though ----------- XOR codes are easier and sloppier. But are actually what's used today despite being imperfect. Let's say you have A, B, C... Z as your data. Parity#1 could be XOR(A, B, Z). If B were missing, Parity#1 XOR A XOR Z can back-calculate B. Parity#2 can be a random set of all previous entries (including Parity#1). Etc. etc. etc. Keep adding XOR parity codes until your probability of reconstruction is high enough to please you. I believe this concept is called a Fountain Code.

halfcat 2y ago
Also I’ve found that while most people (non-tech) don’t have a concept of XOR, they probably took basic algebra and understand 1+?=3 Arithmetic wouldn’t be a good implementation due to integer overflow (a problem XOR doesn’t have) but it’s helpful if you ever have to explain it to the less technical business person who you need to sign off on the purchasing decision.
- genewitch 2y ago
  that's how i used to explain what a nonce was to explain what all the computers were doing to "mine" bitcoin. and then explain "they're instead trying to get a number that has a certain number of zeros in a specific place"
exikyut 2y ago
Is that introduction https://ntrs.nasa.gov/citations/19900019023 https://ntrs.nasa.gov/citations/19900019023 -> https://ntrs.nasa.gov/api/citations/19900019023/downloads/19900019023.pdf https://ntrs.nasa.gov/api/citations/19900019023/downloads/19... [PDF]?
- dragontamer 2y ago
  Yes, this is it. It's a very shallow introduction to Galois Fields but it's just barely enough to reach Reed Solomon encoding and understand error correction codes. As I said earlier: it's a lot of math, even in this simplified form. Abstract conceptual math. But I do find this kind of abstractness very fun.

halfcat 2y ago

Also I’ve found that while most people (non-tech) don’t have a concept of XOR, they probably took basic algebra and understand 1+?=3 Arithmetic wouldn’t be a good implementation due to integer overflow (a problem XOR doesn’t have) but it’s helpful if you ever have to explain it to the less technical business person who you need to sign off on the purchasing decision.

genewitch 2y ago
that's how i used to explain what a nonce was to explain what all the computers were doing to "mine" bitcoin. and then explain "they're instead trying to get a number that has a certain number of zeros in a specific place"

exikyut 2y ago

Is that introduction https://ntrs.nasa.gov/citations/19900019023 https://ntrs.nasa.gov/citations/19900019023 -> https://ntrs.nasa.gov/api/citations/19900019023/downloads/19900019023.pdf https://ntrs.nasa.gov/api/citations/19900019023/downloads/19... [PDF]?

dragontamer 2y ago
Yes, this is it. It's a very shallow introduction to Galois Fields but it's just barely enough to reach Reed Solomon encoding and understand error correction codes. As I said earlier: it's a lot of math, even in this simplified form. Abstract conceptual math. But I do find this kind of abstractness very fun.