Iterators are now working far more reliably and have more extensive tests that randomize inputs and fuzz them to check they keep working.

matrix.cpp

@@ -3,7 +3,24 @@
 #include <fmt/core.h>
 
 using namespace fmt;
-using matrix::Matrix;
+using std::min, std::max;
+
+inline size_t next_x(size_t x, size_t width) {
+  return (x + 1) * ((x + 1) < width);
+}
+
+inline size_t next_y(size_t x, size_t y) {
+  return y + (x == 0);
+}
+
+inline bool at_end(size_t y, size_t height) {
+  return y < height;
+}
+
+inline bool end_row(size_t x, size_t width) {
+  return x == width - 1;
+}
+
 
 namespace matrix {
 
@@ -14,10 +31,9 @@ namespace matrix {
   }
 
   bool each_cell::next() {
-    x++;
-    x *= (x < width);
-    y = y + (x == 0);
-    return y < height;
+    x = next_x(x, width);
+    y = next_y(x, y);
+    return at_end(y, height);
   }
 
   each_row::each_row(Matrix &mat) :
@@ -28,26 +44,59 @@ namespace matrix {
   }
 
   bool each_row::next() {
-    x++;
-    x *= (x < width);
-    y = y + (x == 0);
-    row = x == width - 1;
-    cell = y < height ? $mat[y][x] : -1;
-    return y < height;
+    x = next_x(x, width);
+    y = next_y(x, y);
+    row = end_row(x, width);
+    return at_end(y, height);
+  }
+
+  in_box::in_box(Matrix &mat, size_t from_x, size_t from_y, size_t size) {
+    size_t h = mat.size();
+    size_t w = mat[0].size();
+
+    // keeps it from going below zero
+    // need extra -1 to compensate for the first next()
+    left = max(from_x, size) - size;
+    x = left - 1;  // must be -1 for next()
+    // keeps it from going above width
+    right = min(from_x + size + 1, w);
+
+    // same for these two
+    top = max(from_y, size) - size;
+    y = top - (left == 0);
+    bottom = min(from_y + size + 1, h);
+  }
+
+  bool in_box::next() {
+    // calc next but allow to go to 0 for next
+    x = next_x(x, right);
+    // x will go to 0, which signals new line
+    y = next_y(x, y);  // this must go here
+    // if x==0 then this moves it to min_x
+    x = max(x, left);
+    // and done
+    return at_end(y, bottom);
+  }
+
+  void in_box::dump() {
+    println("BOX: x={},y={}; left={},right={}; top={},bottom={}",
+        x, y, left, right, top, bottom);
   }
 
   void dump(const std::string &msg, Matrix &map, int show_x, int show_y) {
     println("----------------- {}", msg);
 
     for(each_row it{map}; it.next();) {
+      int cell = map[it.y][it.x];
+
       if(int(it.x) == show_x && int(it.y) == show_y) {
-        print("{:x}<", it.cell);
-      } else if(it.cell == WALL_PATH_LIMIT) {
+        print("{:x}<", cell);
+      } else if(cell == WALL_PATH_LIMIT) {
         print("# ");
-      } else if(it.cell > 15) {
+      } else if(cell > 15) {
         print("* ");
       } else {
-        print("{:x} ", it.cell);
+        print("{:x} ", cell);
       }
 
       if(it.row) print("\n");