From fffec5660e726fc658e4eb96a26e38e8117ed16c Mon Sep 17 00:00:00 2001
From: Nickolai Zeldovich <nickolai@csail.mit.edu>
Date: Tue, 10 Feb 2026 09:39:57 -0500
Subject: [PATCH] implement memory.fill and memory.copy

---
 src/parser.rs  |  2 ++
 src/printer.rs | 18 ++++++++++++++++++
 src/wasm.rs    |  2 ++
 3 files changed, 22 insertions(+)

diff --git a/src/parser.rs b/src/parser.rs
index 1ac91eb..29a5e09 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -560,6 +560,8 @@ generate! { instr -> Instr = {
                 0x05 => Instr::ICvtOp(BitSize::B64, intop::CvtOp::TruncSatUF32),
                 0x06 => Instr::ICvtOp(BitSize::B64, intop::CvtOp::TruncSatSF64),
                 0x07 => Instr::ICvtOp(BitSize::B64, intop::CvtOp::TruncSatUF64),
+                0x0a => { run!(expect_byte(0x00)); run!(expect_byte(0x00)); Instr::MemCopy },
+                0x0b => { run!(expect_byte(0x00)); Instr::MemFill },
                 b => err!("Invalid saturation trunctation {:#x}", b),
             }
         }
diff --git a/src/printer.rs b/src/printer.rs
index 42b01ca..46d71c7 100644
--- a/src/printer.rs
+++ b/src/printer.rs
@@ -639,6 +639,24 @@ fn print_instr(
                 }
             }
         }
+        MemFill => {
+            let n = pop!(i32);
+            let v = pop!(i32);
+            let addr = pop!(i32);
+            let addr_end = format!("({} + {})", addr, n);
+
+            Ok(format!("self.memory[{} as usize..{} as usize].fill({} as u8);",
+                addr, addr_end, v))
+        }
+        MemCopy => {
+            let n = pop!(i32);
+            let src = pop!(i32);
+            let dst = pop!(i32);
+            let src_end = format!("({} + {})", src, n);
+
+            Ok(format!("self.memory.copy_within({} as usize..{} as usize, {} as usize);",
+                src, src_end, dst))
+        }
         MemSize => {
             // Note: The spec defines Page Size = 65536
             let inner_mem_size = if opts.fixed_mem_size.is_some() {
diff --git a/src/wasm.rs b/src/wasm.rs
index b03c314..c6f2be6 100644
--- a/src/wasm.rs
+++ b/src/wasm.rs
@@ -273,6 +273,8 @@ pub mod syntax {
             MemStore(MemStore),
             MemSize,
             MemGrow,
+            MemCopy,
+            MemFill,
 
             // Control instructions
             Nop,