change the max square for grains

Author: glennj

config.json

@@ -185,8 +185,7 @@
         "uuid": "99408193-d0ce-4c68-8cab-e680f3ed56a4",
         "practices": [],
         "prerequisites": [],
-        "difficulty": 2,
-        "status": "wip"
+        "difficulty": 2
       },
       {
         "slug": "hello-world",

exercises/practice/grains/.docs/instructions.append.md

@@ -0,0 +1,11 @@
+## Maximum integer value
+
+According to [the Vim docs][number]:
+
+> Assuming 64 bit numbers are used (see v:numbersize) an unsigned number is truncated to 0x7fffffffffffffff or 9223372036854775807.
+
+That means that Vim cannot express any number `2^63` or greater as an integer.
+
+For the purposes of this exercise, we will declare that in Vimland, chess boards are 7x7 and have **49** squares.
+
+[number]: https://vimhelp.org/eval.txt.html#expr-number

exercises/practice/grains/.meta/example.vim

@@ -1,11 +1,11 @@
 function! Square(number) abort
-  if a:number < 1 || a:number > 64
-    throw 'square must be between 1 and 64'
+  if a:number < 1 || a:number > 49
+    throw 'square must be between 1 and 49'
   endif
 
   return float2nr(pow(2, (a:number-1)))
 endfunction
 
 function! Total() abort
-  return float2nr(pow(2, 64) - 1)
+  return float2nr(pow(2, 49) - 1)
 endfunction

exercises/practice/grains/grains.vader

@@ -29,29 +29,28 @@ Execute (grains on square 32):
   let g:expected = 2147483648
   AssertEqual g:expected, Square(g:square)
 
-Execute (grains on square 64):
-  let g:square = 64
-  let g:expected = 9223372036854775807
+Execute (grains on square 49):
+  let g:square = 49
+  let g:expected = 281474976710656
   AssertEqual g:expected, Square(g:square)
 
 Execute (square 0 is invalid):
   let g:square = 0
-  let g:expected = "square must be between 1 and 64"
+  let g:expected = "square must be between 1 and 49"
   AssertThrows call Square(g:square)
   AssertEqual g:expected, g:vader_exception
 
 Execute (negative square is invalid):
   let g:square = -1
-  let g:expected = "square must be between 1 and 64"
+  let g:expected = "square must be between 1 and 49"
   AssertThrows call Square(g:square)
   AssertEqual g:expected, g:vader_exception
 
-Execute (square greater than 64 is invalid):
-  let g:square = 65
-  let g:expected = "square must be between 1 and 64"
+Execute (square greater than 49 is invalid):
+  let g:square = 50
+  let g:expected = "square must be between 1 and 49"
   AssertThrows call Square(g:square)
   AssertEqual g:expected, g:vader_exception
-
 Execute (returns the total number of grains on the board):
-  let g:expected = 9223372036854775807
+  let g:expected = 562949953421311
   AssertEqual g:expected, Total()

exercises/practice/grains/grains.vim

@@ -1,15 +1,15 @@
 "
 " Returns the number of grains on a chessboard square given the grains on each square
 " double from the previous square. 
-" Throws an error if the square is below 1 or above 64.
+" Throws an error if the square is below 1 or above 49.
 "
 " Examples:
 "
 "   :echo Square(16)
 "   32768
 "
 "   :echo Square(-1)
-"   E605: Exception not caught: square must be between 1 and 64
+"   E605: Exception not caught: square must be between 1 and 49
 "
 function! Square(number) abort
   " your code goes here