From c9ff3ce67cce47f83177fec9cb5f7dbed35cd7c3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Aurimas=20Bla=C5=BEulionis?= <0x60@pm.me>
Date: Tue, 28 Mar 2023 20:48:19 +0300
Subject: [PATCH] Add rev jet

---
 rust/ares/src/jets.rs      |  1 +
 rust/ares/src/jets/math.rs | 46 ++++++++++++++++++++++++++++++++++++++
 rust/ares/src/noun.rs      | 38 ++++++++++++++++++++++---------
 3 files changed, 75 insertions(+), 10 deletions(-)

diff --git a/rust/ares/src/jets.rs b/rust/ares/src/jets.rs
index 354b8ad..85534f7 100644
--- a/rust/ares/src/jets.rs
+++ b/rust/ares/src/jets.rs
@@ -61,6 +61,7 @@ pub fn get_jet(jet_name: Noun) -> Option<Jet> {
         tas!(b"rip") => Some(jet_rip),
         tas!(b"met") => Some(jet_met),
         tas!(b"mug") => Some(jet_mug),
+        tas!(b"rev") => Some(jet_rev),
         _ => {
             // eprintln!("Unknown jet: {:?}", jet_name);
             None
diff --git a/rust/ares/src/jets/math.rs b/rust/ares/src/jets/math.rs
index 222d7da..5190cfe 100644
--- a/rust/ares/src/jets/math.rs
+++ b/rust/ares/src/jets/math.rs
@@ -651,6 +651,41 @@ pub fn met(bloq: usize, a: Atom) -> usize {
     }
 }
 
+pub fn jet_rev(stack: &mut NockStack, subject: Noun) -> Result<Noun, JetErr> {
+    let arg = raw_slot(subject, 6);
+    let boz = raw_slot(arg, 2).as_atom()?.as_direct()?.data();
+
+    if boz >= 64 {
+        return Err(NonDeterministic);
+    }
+
+    let boz = boz as usize;
+
+    let len = raw_slot(arg, 6).as_atom()?.as_direct()?.data();
+
+    let dat = raw_slot(arg, 7).as_atom()?;
+
+    let bits = len << boz;
+
+    let mut output = if dat.is_direct() && bits < 64 {
+        unsafe { DirectAtom::new_unchecked(0).as_atom() }
+    } else {
+        unsafe { IndirectAtom::new_raw(stack, ((bits + 7) / 8) as usize, &0).as_atom() }
+    };
+
+    let src = dat.as_bitslice();
+    let dest = output.as_bitslice_mut();
+
+    let len = len as usize;
+    let total_len = len << boz;
+
+    for (start, end) in (0..len).map(|b| (b << boz, (b + 1) << boz)) {
+        dest[start..end].copy_from_bitslice(&src[(total_len - end)..(total_len - start)]);
+    }
+
+    Ok(output.as_noun())
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -1292,4 +1327,15 @@ mod tests {
         let sam = T(s, &[sam, a0, a24, a63, a96, a128]);
         assert_jet(s, jet_mug, sam, D(0x7543cac7));
     }
+
+    #[test]
+    fn test_rev() {
+        let ref mut s = init();
+        let (_a0, a24, _a63, a96, a128) = atoms(s);
+        let sam = T(s, &[D(0), D(60), a24]);
+        assert_jet(s, jet_rev, sam, D(0xc2a6e1000000000));
+        let test = 0x1234567890123u64;
+        let sam = T(s, &[D(3), D(7), D(test)]);
+        assert_jet(s, jet_rev, sam, D(test.swap_bytes() >> 8));
+    }
 }
diff --git a/rust/ares/src/noun.rs b/rust/ares/src/noun.rs
index 068c4a4..3dca704 100644
--- a/rust/ares/src/noun.rs
+++ b/rust/ares/src/noun.rs
@@ -182,6 +182,10 @@ impl DirectAtom {
     pub fn as_bitslice(&self) -> &BitSlice<u64, Lsb0> {
         BitSlice::from_element(&self.0)
     }
+
+    pub fn as_bitslice_mut<'a>(&'a mut self) -> &'a mut BitSlice<u64, Lsb0> {
+        BitSlice::from_element_mut(&mut self.0)
+    }
 }
 
 impl fmt::Display for DirectAtom {
@@ -372,10 +376,18 @@ impl IndirectAtom {
         unsafe { self.to_raw_pointer().add(2) as *const u64 }
     }
 
+    pub fn data_pointer_mut(&mut self) -> *mut u64 {
+        unsafe { self.to_raw_pointer_mut().add(2) as *mut u64 }
+    }
+
     pub fn as_slice(&self) -> &[u64] {
         unsafe { from_raw_parts(self.data_pointer(), self.size()) }
     }
 
+    pub fn as_mut_slice(&mut self) -> &mut [u64] {
+        unsafe { from_raw_parts_mut(self.data_pointer_mut(), self.size()) }
+    }
+
     pub fn as_bytes(&self) -> &[u8] {
         unsafe { from_raw_parts(self.data_pointer() as *const u8, self.size() << 3) }
     }
@@ -385,6 +397,10 @@ impl IndirectAtom {
         BitSlice::from_slice(self.as_slice())
     }
 
+    pub fn as_bitslice_mut<'a>(&'a mut self) -> &'a mut BitSlice<u64, Lsb0> {
+        BitSlice::from_slice_mut(self.as_mut_slice())
+    }
+
     pub fn as_ubig<S: Stack>(&self, stack: &mut S) -> UBig {
         UBig::from_le_bytes_stack(stack, self.as_bytes())
     }
@@ -595,16 +611,10 @@ impl Atom {
         let bit_size = big.bit_len();
         let buffer = big.to_le_bytes_stack();
         if bit_size < 64 {
-            #[rustfmt::skip]
-            let value: u64 =
-                  if bit_size == 0  { 0 } else { (buffer[0] as u64)
-                | if bit_size <= 8  { 0 } else { (buffer[1] as u64) << 8
-                | if bit_size <= 16 { 0 } else { (buffer[2] as u64) << 16
-                | if bit_size <= 24 { 0 } else { (buffer[3] as u64) << 24
-                | if bit_size <= 32 { 0 } else { (buffer[4] as u64) << 32
-                | if bit_size <= 40 { 0 } else { (buffer[5] as u64) << 40
-                | if bit_size <= 48 { 0 } else { (buffer[6] as u64) << 48
-                | if bit_size <= 56 { 0 } else { (buffer[7] as u64) << 56 } } } } } } } };
+            let mut value = 0u64;
+            for i in (0..bit_size).step_by(8) {
+                value |= (buffer[i / 8] as u64) << i;
+            }
             unsafe { DirectAtom::new_unchecked(value).as_atom() }
         } else {
             let byte_size = (big.bit_len() + 7) >> 3;
@@ -652,6 +662,14 @@ impl Atom {
         }
     }
 
+    pub fn as_bitslice_mut<'a>(&'a mut self) -> &'a mut BitSlice<u64, Lsb0> {
+        if self.is_indirect() {
+            unsafe { self.indirect.as_bitslice_mut() }
+        } else {
+            unsafe { self.direct.as_bitslice_mut() }
+        }
+    }
+
     pub fn as_ubig<S: Stack>(self, stack: &mut S) -> UBig {
         if self.is_indirect() {
             unsafe { self.indirect.as_ubig(stack) }