JS: fix for overlap with copyMutableByteArray# (#23033)

The code wasn't taking into account some kind of overlap.

cgrun070 has been extended to test the missing case.

1 files changed, 22 insertions, 1 deletions

diff --git a/rts/js/mem.js b/rts/js/mem.js
index c1f586c282..3dcdc7979f 100644
--- a/rts/js/mem.js
+++ b/rts/js/mem.js
@@ -531,12 +531,17 @@ function h$sliceArray(a, start, n) {
   return r;
 }
 
+//////////////////////////////////////////////////////////
+//
 // copy between two mutable arrays. Range may overlap
+// so we check which offset is bigger to make a front-to-back or
+// back-to-front traversal of the arrays.
+
 function h$copyMutableArray(a1,o1,a2,o2,n) {
   if (n <= 0) return;
 
   if (o1 < o2) {
-    for (var i=n-1;i>=0;i--) { // start from the end to handle potential overlap
+    for (var i=n-1;i>=0;i--) {
       a2[o2+i] = a1[o1+i];
     }
   } else {
@@ -546,6 +551,22 @@ function h$copyMutableArray(a1,o1,a2,o2,n) {
   }
 }
 
+function h$copyMutableByteArray(a1,o1,a2,o2,n) {
+  if (n <= 0) return;
+
+  if (o1 < o2) {
+    for (var i=n-1;i>=0;i--) {
+      a2.u8[o2+i] = a1.u8[o1+i];
+    }
+  } else {
+    for (var i=0;i<n;i++) {
+      a2.u8[o2+i] = a1.u8[o1+i];
+    }
+  }
+}
+
+//////////////////////////////////////////////////////////
+
 function h$memcpy() {
   if(arguments.length === 3) {  // ByteArray# -> ByteArray# copy
     var dst = arguments[0];