Fix a bytes bug when creating slices of slices with a non-zero offset.

lib/bytes.cc

@@ -138,14 +138,14 @@ uint8_t& Bytes::operator [] (unsigned pos)
 
 Bytes Bytes::slice(unsigned start, unsigned len) const
 {
-    start += _low;
-    unsigned end = start + len;
-    if (start >= _high)
+    unsigned datastart = _low + start;
+    unsigned dataend = datastart + len;
+    if (datastart >= _high)
     {
         /* Asking for a completely out-of-range slice --- just return zeroes. */
         return Bytes(len);
     }
-    else if (end > _high)
+    else if (dataend > _high)
     {
         /* Can't share the buffer, as we need to zero-pad the end. */
         Bytes b(len);
@@ -155,7 +155,7 @@ Bytes Bytes::slice(unsigned start, unsigned len) const
     else
     {
         /* Use the magic of shared_ptr to share the data. */
-        Bytes b(_data, start, end);
+        Bytes b(_data, datastart, dataend);
         return b;
     }
 }

lib/bytes.h

@@ -65,6 +65,16 @@ public:
     void writeToFile(const std::string& filename) const;
 	void writeTo(std::ostream& stream) const;
 
+	template <class T> std::vector<T> toVector() const
+	{
+		std::vector<T> v(size());
+		for (int i=0; i<size(); i++)
+			v[i] = (*this)[i];
+		return v;
+	}
+
+	std::vector<uint8_t> toVector() const;
+
 private:
     std::shared_ptr<std::vector<uint8_t>> _data;
     unsigned _low;

tests/bytes.cc

@@ -1,5 +1,8 @@
 #include "globals.h"
 #include "bytes.h"
+#include "snowhouse/snowhouse.h"
+
+using namespace snowhouse;
 
 static void check_oob(Bytes& b, unsigned pos)
 {
@@ -113,6 +116,13 @@ static void test_slice()
     
     bs = b.slice(4, 2);
     assert((bs == Bytes{ 0, 0 }));
+    
+    bs = b.slice(2, 2);
+    assert((bs == Bytes{ 3, 0 }));
+
+	bs = b.slice(1, 4);
+	bs = bs.slice(1, 4);
+	AssertThat(bs.toVector<int>(), Equals(Bytes{ 3, 0, 0, 0 }.toVector<int>()));
 }
 
 static void test_tobits()