First pass at nqp::decode(...).

Author: jnthn

src/vm/jvm/QAST/Compiler.nqp

@@ -2074,6 +2074,7 @@ QAST::OperationsJAST.add_core_op('rindex',  -> $qastcomp, $op {
 
 QAST::OperationsJAST.map_classlib_core_op('codepointfromname', $TYPE_OPS, 'codepointfromname', [$RT_STR], $RT_INT);
 QAST::OperationsJAST.map_classlib_core_op('encode', $TYPE_OPS, 'encode', [$RT_STR, $RT_STR, $RT_OBJ], $RT_OBJ, :tc);
+QAST::OperationsJAST.map_classlib_core_op('decode', $TYPE_OPS, 'decode', [$RT_OBJ, $RT_STR], $RT_STR, :tc);
 
 # serialization context opcodes
 QAST::OperationsJAST.map_classlib_core_op('sha1', $TYPE_OPS, 'sha1', [$RT_STR], $RT_STR);

src/vm/jvm/runtime/org/perl6/nqp/runtime/Ops.java

@@ -16,6 +16,7 @@
 import java.math.BigInteger;
 import java.math.RoundingMode;
 import java.nio.ByteBuffer;
+import java.nio.charset.Charset;
 import java.nio.file.Files;
 import java.nio.file.LinkOption;
 import java.nio.file.Path;
@@ -2979,6 +2980,57 @@ else if (encoding.equals("utf32")) {
         }
     }
 
+    public static String decode8(SixModelObject buf, String csName, ThreadContext tc) {
+        ByteBuffer bb;
+        if (buf instanceof VMArrayInstance_i8) {
+            VMArrayInstance_i8 bufi8 = (VMArrayInstance_i8)buf;
+            bb = bufi8.slots != null
+                ? ByteBuffer.wrap(bufi8.slots, bufi8.start, bufi8.elems)
+                : ByteBuffer.allocate(0);
+        }
+        else {
+            int n = (int)buf.elems(tc);
+            bb = ByteBuffer.allocate(n);
+            for (int i = 0; i < n; i++) {
+                buf.at_pos_native(tc, i);
+                bb.put((byte)tc.native_i);
+            }
+        }
+        return Charset.forName(csName).decode(bb).toString();
+    }
+    public static String decode(SixModelObject buf, String encoding, ThreadContext tc) {
+        if (encoding.equals("utf8")) {
+            return decode8(buf, "UTF-8", tc);
+        }
+        else if (encoding.equals("ascii")) {
+            return decode8(buf, "US-ASCII", tc);
+        }
+        else if (encoding.equals("iso-8859-1")) {
+            return decode8(buf, "ISO-8859-1", tc);
+        }
+        else if (encoding.equals("utf16")) {
+            int n = (int)buf.elems(tc);
+            StringBuilder sb = new StringBuilder(n);
+            for (int i = 0; i < n; i++) {
+                buf.at_pos_native(tc, i);
+                sb.append((char)tc.native_i);
+            }
+            return sb.toString();
+        }
+        else if (encoding.equals("utf32")) {
+            int n = (int)buf.elems(tc);
+            StringBuilder sb = new StringBuilder(n);
+            for (int i = 0; i < n; i++) {
+                buf.at_pos_native(tc, i);
+                sb.appendCodePoint((int)tc.native_i);
+            }
+            return sb.toString();
+        }
+        else {
+            throw ExceptionHandling.dieInternal(tc, "Unknown encoding '" + encoding + "'");
+        }
+    }
+    
     private static final int CCLASS_ANY          = 65535;
     private static final int CCLASS_UPPERCASE    = 1;
     private static final int CCLASS_LOWERCASE    = 2;