From 8b9d6ba3824561ca641ad8db23878ce5b4b6b6ca Mon Sep 17 00:00:00 2001
From: arkpar <arkady.paronyan@gmail.com>
Date: Wed, 2 Jan 2019 16:27:51 +0300
Subject: [PATCH] Track lowest_used in copy, etc.

---
 src/memory.rs | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/src/memory.rs b/src/memory.rs
index 626fb7a..3005e0b 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -391,6 +391,10 @@ impl MemoryInstance {
         let (read_region, write_region) =
             self.checked_region_pair(&mut buffer, src_offset, len, dst_offset, len)?;
 
+		if dst_offset < self.lowest_used.get() {
+			self.lowest_used.set(dst_offset);
+		}
+
         unsafe {
             ::core::ptr::copy(
                 buffer[read_region.range()].as_ptr(),
@@ -430,6 +434,10 @@ impl MemoryInstance {
             )));
         }
 
+		if dst_offset < self.lowest_used.get() {
+			self.lowest_used.set(dst_offset);
+		}
+
         unsafe {
             ::core::ptr::copy_nonoverlapping(
                 buffer[read_region.range()].as_ptr(),
@@ -469,6 +477,10 @@ impl MemoryInstance {
             .checked_region(&mut dst_buffer, dst_offset, len)?
             .range();
 
+		if dst_offset < self.lowest_used.get() {
+			self.lowest_used.set(dst_offset);
+		}
+
         dst_buffer[dst_range].copy_from_slice(&src_buffer[src_range]);
 
         Ok(())
@@ -485,6 +497,11 @@ impl MemoryInstance {
         let mut buffer = self.buffer.borrow_mut();
 
         let range = self.checked_region(&mut buffer, offset, len)?.range();
+
+		if dst_offset < self.lowest_used.get() {
+			self.lowest_used.set(dst_offset);
+		}
+
         for val in &mut buffer[range] {
             *val = new_val
         }
@@ -497,12 +514,7 @@ impl MemoryInstance {
     ///
     /// Returns `Err` if the specified region is out of bounds.
     pub fn zero(&self, offset: usize, len: usize) -> Result<(), Error> {
-        if (offset + len) >= self.buffer.borrow().len() {
-            self.buffer.borrow_mut().resize(offset,  0u8);
-            Ok(())
-        } else {
-            self.clear(offset, 0, len)
-        }
+		self.clear(offset, 0, len)
     }
 
     /// Provides direct access to the underlying memory buffer.