add value and type constructors for variable-length buffers and sha256 ctx8

CHANGELOG.md

@@ -1,3 +1,10 @@
+# Unreleased
+
+* Add `Value` and `Type` constructors for variable-length buffers and SHA256 `Ctx8` contexts;
+  change the signature of `Final::two_two_n` to return a result rather than panicking when `n`
+  is too large; add infallible `Final::two_two_n_fixed` for when `n` is known at compile-time
+  [#372][https://github.com/BlockstreamResearch/rust-simplicity/pull/372)
+
 # 0.8.0 - 2026-05-28
 
 * Add runtime jet type check in `Context` [#361](https://github.com/BlockstreamResearch/rust-simplicity/pull/361)

jets-bench/src/data_structures.rs

@@ -63,7 +63,7 @@ pub fn var_len_buf_from_slice(v: &[u8], n: usize) -> Result<Value, EarlyEndOfStr
     let mut iter = BitIter::new(v.iter().copied());
     let mut res = None;
     for i in (0..n).rev() {
-        let ty = Final::two_two_n(i + 3);
+        let ty = Final::two_two_n(i + 3).unwrap();
         let v = if v.len() & 1 << i != 0 {
             let val = Value::from_compact_bits(&mut iter, &ty)?;
             Value::some(val)
@@ -414,7 +414,7 @@ impl BenchSample for SimplicityPoint {
 // Sample genesis pegin with 50% probability
 pub fn genesis_pegin() -> Value {
     if rand::random() {
-        Value::none(Final::two_two_n(8))
+        Value::none(Final::two_two_n_fixed::<8>())
     } else {
         let genesis_hash = rand::random::<[u8; 32]>();
         Value::some(Value::u256(genesis_hash))

src/jet/type_name.rs

@@ -43,12 +43,12 @@ impl TypeName {
         for c in self.0.iter().rev() {
             match c {
                 b'1' => stack.push(Final::unit()),
-                b'2' => stack.push(Final::two_two_n(0)),
-                b'c' => stack.push(Final::two_two_n(3)),
-                b's' => stack.push(Final::two_two_n(4)),
-                b'i' => stack.push(Final::two_two_n(5)),
-                b'l' => stack.push(Final::two_two_n(6)),
-                b'h' => stack.push(Final::two_two_n(8)),
+                b'2' => stack.push(Final::two_two_n_fixed::<0>()),
+                b'c' => stack.push(Final::two_two_n_fixed::<3>()),
+                b's' => stack.push(Final::two_two_n_fixed::<4>()),
+                b'i' => stack.push(Final::two_two_n_fixed::<5>()),
+                b'l' => stack.push(Final::two_two_n_fixed::<6>()),
+                b'h' => stack.push(Final::two_two_n_fixed::<8>()),
                 b'+' | b'*' => {
                     let left = stack.pop().expect("Illegal type name syntax!");
                     let right = stack.pop().expect("Illegal type name syntax!");

src/merkle/tmr.rs

@@ -236,11 +236,129 @@ impl Tmr {
         ])),
     ];
 
+    /// The TMRs of the types (TWO^8)^<(2^(N + 1)) for small values of n
+    #[rustfmt::skip]
+    pub const BUFFER8_TWO_N_PLUS_ONE: [Tmr; 16] = [
+        Tmr(Midstate([
+            0x66, 0x8c, 0x79, 0xa6, 0xf0, 0xe0, 0x86, 0xa6,
+            0x2d, 0x73, 0xf0, 0xc6, 0x52, 0xb1, 0x5c, 0x56,
+            0xb1, 0xd3, 0x53, 0x68, 0xe1, 0xff, 0xad, 0x76,
+            0xc9, 0xd4, 0xdb, 0xae, 0xb5, 0x2d, 0xe6, 0x2f,
+        ])),
+        Tmr(Midstate([
+            0x9f, 0x91, 0xf5, 0x19, 0x9b, 0xb8, 0x16, 0x7a,
+            0x3b, 0x6c, 0xf8, 0xd0, 0x39, 0x75, 0x6e, 0x1b,
+            0x33, 0x18, 0x42, 0x6e, 0xef, 0x3a, 0x9b, 0xa0,
+            0x90, 0x2c, 0x91, 0xdc, 0x5f, 0x7e, 0x63, 0x39,
+        ])),
+        Tmr(Midstate([
+            0x16, 0x98, 0x45, 0xb0, 0xe2, 0xf0, 0x4a, 0x83,
+            0x76, 0xfe, 0x91, 0x14, 0xbd, 0x35, 0x3a, 0x29,
+            0xe9, 0xb7, 0x80, 0x42, 0xb7, 0x70, 0x1b, 0xa1,
+            0x6d, 0x02, 0xc4, 0x62, 0x18, 0xef, 0x8b, 0xdf,
+        ])),
+        Tmr(Midstate([
+            0xbd, 0x59, 0x57, 0x8c, 0x45, 0x78, 0xfe, 0xc4,
+            0xef, 0x2a, 0x29, 0xc1, 0xad, 0xea, 0x4c, 0xe1,
+            0x30, 0x6c, 0x1a, 0x2b, 0x10, 0xd6, 0x18, 0xbc,
+            0x58, 0x44, 0x67, 0x84, 0x17, 0x97, 0x3b, 0x8e,
+        ])),
+        Tmr(Midstate([
+            0x88, 0xd1, 0x8c, 0x11, 0x5f, 0x86, 0x54, 0x40,
+            0x5f, 0xd7, 0x1d, 0xe8, 0x7e, 0x6f, 0xf0, 0x80,
+            0x6c, 0x5d, 0xa7, 0x97, 0xca, 0xaf, 0x48, 0xe2,
+            0x47, 0xea, 0xcc, 0x43, 0x99, 0x96, 0x89, 0x1a,
+        ])),
+        Tmr(Midstate([
+            0x90, 0x65, 0x22, 0xe1, 0x6d, 0xf3, 0x6f, 0x83,
+            0xa4, 0x50, 0x32, 0x8a, 0xf8, 0x4e, 0x2f, 0x3e,
+            0x52, 0xf6, 0xd6, 0x49, 0xa7, 0x88, 0xe3, 0xb2,
+            0x1c, 0xca, 0xe3, 0xcd, 0x9a, 0x24, 0x66, 0x77,
+        ])),
+        Tmr(Midstate([
+            0x3a, 0xba, 0x4c, 0xce, 0x0e, 0x46, 0xc5, 0x54,
+            0xb4, 0x4f, 0x70, 0x21, 0x3d, 0x4d, 0x8b, 0xd8,
+            0xe8, 0xf1, 0x7e, 0x2b, 0xd1, 0x7b, 0xdf, 0xb7,
+            0x15, 0x0a, 0xdf, 0xfd, 0x9a, 0xdf, 0x80, 0x9d,
+        ])),
+        Tmr(Midstate([
+            0x7d, 0x81, 0x2a, 0xf0, 0x44, 0xcb, 0x04, 0xd2,
+            0xaf, 0x4f, 0xc8, 0xe9, 0xb5, 0x30, 0x66, 0x03,
+            0x9b, 0xd5, 0x89, 0x2a, 0x56, 0xa5, 0xd5, 0x64,
+            0x1c, 0x5c, 0x58, 0xc8, 0x6e, 0xed, 0x8a, 0x35,
+        ])),
+        Tmr(Midstate([
+            0x23, 0x0e, 0xa9, 0x70, 0x03, 0x3e, 0x47, 0xc5,
+            0x61, 0x68, 0x1e, 0xe7, 0x20, 0x58, 0xb9, 0xc0,
+            0x75, 0x5b, 0x8d, 0x87, 0x22, 0x80, 0x18, 0x4f,
+            0x2e, 0x3f, 0xe3, 0x93, 0xc0, 0x47, 0x8f, 0x1a,
+        ])),
+        Tmr(Midstate([
+            0x6e, 0x90, 0x88, 0x04, 0x20, 0x46, 0x2b, 0x84,
+            0xf2, 0x16, 0x30, 0x2a, 0x09, 0x56, 0x9c, 0xc8,
+            0xd4, 0x47, 0x54, 0x4a, 0xcd, 0x8a, 0xbc, 0x53,
+            0xd8, 0xa7, 0xcf, 0x21, 0x9b, 0x44, 0x9c, 0x95,
+        ])),
+        Tmr(Midstate([
+            0x7a, 0xd1, 0x5d, 0xed, 0x85, 0x02, 0xa6, 0xf1,
+            0x1e, 0xb8, 0xa4, 0x9b, 0x25, 0xc8, 0xd7, 0x62,
+            0xa0, 0xfe, 0x00, 0x4f, 0xb5, 0x7d, 0x73, 0x43,
+            0xbd, 0xf4, 0x90, 0xed, 0x7e, 0xd2, 0xf4, 0x07,
+        ])),
+        Tmr(Midstate([
+            0xaa, 0x30, 0x30, 0x15, 0x71, 0xcf, 0x8d, 0x2d,
+            0x64, 0xe9, 0x65, 0x4b, 0x0c, 0xbd, 0xe0, 0x54,
+            0x01, 0x77, 0xab, 0xc2, 0xf2, 0xef, 0xfb, 0x7f,
+            0x05, 0x2e, 0x27, 0xa8, 0xcc, 0xcc, 0xee, 0x62,
+        ])),
+        Tmr(Midstate([
+            0x28, 0x6d, 0x4d, 0x57, 0x6d, 0xb8, 0xe8, 0x45,
+            0x00, 0x9c, 0x74, 0x84, 0xe0, 0x0a, 0x9f, 0xa3,
+            0xf3, 0x18, 0xa8, 0x21, 0x9e, 0x38, 0x66, 0x2c,
+            0xda, 0x11, 0x75, 0x78, 0x22, 0xe4, 0x53, 0xbb,
+        ])),
+        Tmr(Midstate([
+            0x10, 0x56, 0xa7, 0x17, 0xdc, 0x0c, 0x86, 0xb7,
+            0x49, 0x97, 0x5e, 0x9c, 0x36, 0x4a, 0xb5, 0xa6,
+            0x64, 0x77, 0xc4, 0x2d, 0xe1, 0x6e, 0x5b, 0x05,
+            0x29, 0x81, 0x4f, 0x4c, 0xba, 0x95, 0x7c, 0xb3,
+        ])),
+        Tmr(Midstate([
+            0x94, 0x59, 0x0e, 0xf5, 0x66, 0x10, 0xaa, 0x7f,
+            0xec, 0x46, 0x5b, 0x72, 0x32, 0xab, 0xa3, 0xf4,
+            0x7c, 0x94, 0x2b, 0x8e, 0x8d, 0xc8, 0x76, 0x82,
+            0x51, 0xd3, 0x70, 0x2c, 0x99, 0xb9, 0xef, 0xef,
+        ])),
+        Tmr(Midstate([
+            0xd0, 0x7f, 0x71, 0xb7, 0xcd, 0x48, 0xb8, 0x50,
+            0xad, 0x09, 0x06, 0x8b, 0x9b, 0x48, 0xe0, 0xf8,
+            0x5f, 0x84, 0xc0, 0x1b, 0x34, 0x58, 0x6a, 0x51,
+            0x34, 0x61, 0xfa, 0xf7, 0x6d, 0x54, 0x34, 0x64,
+        ])),
+    ];
+
+    /// The TMR of the `Ctx8` type used by the SHA256 jets.
+    #[rustfmt::skip]
+    pub const CTX8: Tmr = Tmr(Midstate([
+        0x8d, 0x5c, 0xe5, 0xf6, 0xeb, 0xfc, 0x70, 0x61,
+        0xe7, 0x91, 0x16, 0xbd, 0xf6, 0x6f, 0xb4, 0xe4,
+        0xc6, 0xca, 0x32, 0xa0, 0x1c, 0xda, 0x48, 0xf6,
+        0xed, 0xc1, 0x0a, 0xee, 0xfd, 0x31, 0x0e, 0x8c,
+    ]));
+
     /// The TMR for the unit type
     pub const fn unit() -> Tmr {
         Self::UNIT_IV
     }
 
+    /// The TMR for the successor of a type.
+    ///
+    /// Given a type `X`, we define its successor `S X` as `1 + X`.
+    /// In Rust notation this would be `Option<X>`.
+    pub fn successor(self) -> Tmr {
+        Self::SUM_IV.update(Tmr::unit(), self)
+    }
+
     /// The TMR for the sum of two types, whose TMRs are given
     pub fn sum(tmr1: Tmr, tmr2: Tmr) -> Tmr {
         Self::SUM_IV.update(tmr1, tmr2)
@@ -256,8 +374,9 @@ impl Tmr {
 mod tests {
     use super::*;
 
+    use crate::jet::Jet;
     use crate::merkle::bip340_iv;
-    use crate::types;
+    use crate::types::{self, Final};
 
     #[test]
     fn ivs() {
@@ -317,4 +436,47 @@ mod tests {
             }
         });
     }
+
+    #[test]
+    fn const_buffer8() {
+        use std::sync::Arc;
+
+        let two_8_tmr = Tmr::TWO_TWO_N[3];
+        let buf_0_tmr = two_8_tmr.successor();
+
+        let two_8 = Final::two_two_n_fixed::<3>();
+        let buf_0 = Arc::clone(&two_8).successor();
+
+        assert_eq!(buf_0, Final::buffer8_two_n_plus_one(0).unwrap());
+        assert_eq!(two_8.tmr(), two_8_tmr);
+        assert_eq!(buf_0.tmr(), buf_0_tmr);
+        assert_eq!(buf_0_tmr, Tmr::BUFFER8_TWO_N_PLUS_ONE[0]);
+
+        let mut tmr = buf_0_tmr;
+        let mut fin = buf_0;
+        assert_eq!(Tmr::BUFFER8_TWO_N_PLUS_ONE.len(), 16);
+        for n in 1..Tmr::BUFFER8_TWO_N_PLUS_ONE.len() {
+            tmr = Tmr::product(Tmr::TWO_TWO_N[n + 3].successor(), tmr);
+            fin = Final::product(Final::two_two_n(n + 3).unwrap().successor(), fin);
+
+            assert_eq!(fin.tmr(), tmr);
+            assert_eq!(fin, Final::buffer8_two_n_plus_one(n).unwrap());
+            assert_eq!(tmr, Tmr::BUFFER8_TWO_N_PLUS_ONE[n]);
+
+            // For the case of n == 5, i.e. a 63-byte buffer (63 = 2^(n + 1) - 1),
+            // we can check against the SHA256 Ctx8 type to make sure that our
+            // computations are actually correct.
+            if n == 5 {
+                let extra_ctx_stuff = Final::product(
+                    Final::two_two_n_fixed::<6>(), // 2^64
+                    Final::two_two_n_fixed::<8>(), // 2^256
+                );
+                let synthetic_ctx_ty = Final::product(Arc::clone(&fin), extra_ctx_stuff);
+                let actual_ctx_ty = crate::jet::Core::Sha256Ctx8Init.target_ty().to_final();
+                assert_eq!(synthetic_ctx_ty, actual_ctx_ty,);
+                assert_eq!(synthetic_ctx_ty, Final::ctx8());
+                assert_eq!(synthetic_ctx_ty.tmr(), Tmr::CTX8);
+            }
+        }
+    }
 }