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jets-bench: fix multiple issues with Ctx8 encoding #319

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Merged
merged 1 commit into from
Nov 24, 2025
+17 −15
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jets-bench: fix multiple issues with Ctx8 encoding #319

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32 changes: 17 additions & 15 deletions jets-bench/src/data_structures.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ use simplicity::{
/// length.
#[derive(Clone)]
pub struct SimplicityCtx8 {
buffer: [u8; 512],
buffer: [u8; 64],
h: [u32; 8],
length: usize,
}
Expand All @@ -31,7 +31,7 @@ impl Default for SimplicityCtx8 {
0x5be0cd19,
],
length: 0,
buffer: [0; 512],
buffer: [0; 64],
}
}
}
Expand All @@ -45,24 +45,26 @@ impl SimplicityCtx8 {
}
}

/// Read bytes from a Simplicity buffer of type (TWO^8)^<2^(n+1) as [`Value`].
/// Read bytes from a Simplicity buffer of type (TWO^8)^<2^n as [`Value`].
/// The notation X^<2 is notation for the type (S X)
/// The notation X^<(2*n) is notation for the type S (X^n) * X^<n
///
/// Cannot represent >= 2**16 bytes 0 <= n < 16 as simplicity consensus rule.
/// There is a precondition that 0 <= n <= 16.
///
/// # Panics:
///
/// Panics if the length of the slice is >= 2^(n + 1) bytes
pub fn var_len_buf_from_slice(v: &[u8], mut n: usize) -> Result<Value, EarlyEndOfStreamError> {
// Simplicity consensus rule for n < 16 while reading buffers.
assert!(n < 16);
assert!(v.len() < (1 << (n + 1)));
/// Panics if the length of the slice is >= 2^n bytes or if n > 16.
pub fn var_len_buf_from_slice(v: &[u8], n: usize) -> Result<Value, EarlyEndOfStreamError> {
// This precondition can probably be removed or relaxed, though
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@canndrew canndrew Nov 21, 2025

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It wasn't immediately obvious what this code was doing, so I had to read the doc comment, write it myself, then compare my code against this. It might've been clearer if while n > 0 was replaced with for i in (0..n).rev() (since the loop is just counting down to zero), plus that means you can get rid of (n - 1) (subtraction on usize always makes me do a double-take) and it changes two_two_n(n + 2) to two_two_n(i + 3) (where + 3 is obviously just a bytes-to-bits conversion).

That's all nit-picking though. Otherwise LGTM.

// we have no need to do so and it may require changing the type
// of 'n' to something larger.
assert!(n <= 16);
assert!(v.len() < 1 << n);
let mut iter = BitIter::new(v.iter().copied());
let mut res = None;
while n > 0 {
let ty = Final::two_two_n(n);
let v = if v.len() >= (1 << (n + 1)) {
for i in (0..n).rev() {
let ty = Final::two_two_n(i + 3);
let v = if v.len() & 1 << i != 0 {
let val = Value::from_compact_bits(&mut iter, &ty)?;
Value::some(val)
} else {
Expand All @@ -72,8 +74,8 @@ pub fn var_len_buf_from_slice(v: &[u8], mut n: usize) -> Result<Value, EarlyEndO
Some(prod) => Some(Value::product(prod, v)),
None => Some(v),
};
n -= 1;
}
assert_eq!(iter.next(), None);
Ok(res.unwrap_or(Value::unit()))
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@roconnor-blockstream roconnor-blockstream Nov 20, 2025

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So I'm going to actually recommend that you have precondition that 1 <= n, because 𝟙 is not actually a buffer type, and if people are passing 0 here it is probably a big mistake.

If you strongly disagree then you can keep the code as it is.

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@roconnor-blockstream roconnor-blockstream Nov 20, 2025 •
edited
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Actually I take that back. Arguably 𝟙 is a buffer type for a degenerate empty buffer type. So you can leave the code as is.

}

Expand Down Expand Up @@ -157,8 +159,8 @@ pub trait SimplicityEncode {

impl SimplicityEncode for SimplicityCtx8 {
fn value(&self) -> Value {
let buf_len = self.length % 512;
let buf = var_len_buf_from_slice(&self.buffer[..buf_len], 8).unwrap();
let buf_len = self.length % 64;
let buf = var_len_buf_from_slice(&self.buffer[..buf_len], 6).unwrap();
let len = Value::u64(self.length as u64);
// convert to 32 byte array
let mut arr = [0u8; 32];
Expand Down