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finish with endianness section

This commit is contained in:
Joe Ardent 2023-06-28 12:52:54 -07:00
parent e7bd1bd5f8
commit 64d5597802
1 changed files with 17 additions and 13 deletions
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30
content/rnd/a_serialized_mystery/index.md
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@ -188,7 +188,7 @@ impl Decode<'_, Sqlite> for DbId {
fn decode(value: SqliteValueRef<'_>) -> Result<Self, sqlx::error::BoxDynError> {
let bytes = <&[u8] as Decode<Sqlite>>::decode(value)?;
let bytes: [u8; 16] = bytes.try_into().unwrap_or_default();
Ok(u128::from_be_bytes(bytes).into())
Ok(u128::from_ne_bytes(bytes).into())
}
}
```
@ -313,25 +313,29 @@ not storing them in string from. Fundamentally, the ULID was a simple [128-bit p
integer](https://doc.rust-lang.org/std/primitive.u128.html), capable of holding values between 0 and
340,282,366,920,938,463,463,374,607,431,768,211,455.
But there's a problem: we're storing our ID in the database as a sequence of 16 bytes. I was asking
But there's a problem: I was storing the ID in the database as a sequence of 16 bytes. I was asking
for those bytes in "native endian", which in my case, meant "little endian". If you're not familiar
with endianness, there are two varieties: big, and little. "Big" makes the most sense; if you see a
number like "512", it's big-endian; the end is the part that's left-most, and "big" means that it is
the most-significant-digit. This is the same as what westerners think of as "normal" numbers. In the
number "512", the "most significant digit" is `5`, which correspends to `500`, which is added to the
next-most-significant digit, `1`, corresponding to `10`, which is added to the next-most-significant
digit, which is also the least-most-significant-digit, which is `2`, which is just `2`, giving us
the full number `512`.
with endianness, there are two varieties: big, and little. "Big" makes the most sense for a lot of
people; if you see a number like "512", it's big-endian; the end is the part that's left-most, and
"big" means that it is the most-significant-digit. This is the same as what westerners think of as
"normal" numbers. In the number "512", the "most significant digit" is `5`, which correspends to
`500`, which is added to the next-most-significant digit, `1`, corresponding to `10`, which is added
to the next-most-significant digit, which is also the least-most-significant-digit, which is `2`,
which is just `2`, giving us the full number `512`.
If we put the least-significant-digit first, we'd write the number `512` as "215"; the order when
written out would be reversed. This means that the lexicographic sort of `512, 521` would have "125"
come before "215", which is backwards.
Little-endiannes is like that. If a multibyte value is on a little-endian system, the least-significant
bytes will come first, and the sorting would be non-numeric.
Little-endiannes is like that. If a multibyte numeric value is on a little-endian system, the
least-significant bytes will come first, and a lexicographic sorting of those bytes would be
non-numeric.
Unfortunaly, my computer is based on the Intel x86 instruction set, which means that it represents
numbers in "little endian" form. This means that
The solution, though, is simple: just write them out in big-endian order! This was literally a
one-line change in the code, to switch from `to_ne_bytes()` ("ne" for "native endian") to
`to_be_bytes()`.
Boom. Sorted.
## The actual problem