Add whole sqrt example

examples/.gitignore

@@ -8,3 +8,4 @@ seq
 fib
 gol
 fizz-buzz
+whole-sqrt

examples/whole-sqrt.porth

@@ -0,0 +1,51 @@
+include "std.porth"
+
+// in : s n
+// out: ((s // n) + n) // 2
+// one iteration of the Babylonian method
+macro _apply
+  over over /
+  over +
+  2 /
+  swap drop
+  swap drop
+end
+
+// in : s
+// out: floor(sqrt(s))
+// uses Babylonian method
+macro whole_sqrt
+  if dup 1 = do  // 1 is a special case for Babylonian method
+    drop 1  // sqrt(1) == 1
+  else if dup 0 < do
+    "\nValue error, input: " eputs dup print
+    here eputs " Can't get sqrt from negative number" eputs 1 exit
+  else  // general case
+    dup  // `previous`
+    dup 2 /  // `current` - firt guess
+    while 2dup swap < do
+      swap drop // we don't need `previous` anymore
+      // dup print // debug
+      2dup _apply // apply one iteration and get `current`
+      // old `current` becomes `previous`
+    end
+    drop // drop `current`
+    swap drop // drop `s`
+    // leave `previous`
+  end end
+end
+
+// in : number
+// out: number == whole_sqrt(number)**2
+macro is_perfect_square
+  dup whole_sqrt dup * =
+end
+
+// test is_perfect_square
+100 while dup -101 != do
+  if dup is_perfect_square do
+    "Perfect square: " puts dup print
+  end
+  1 -
+end
+drop

examples/whole-sqrt.txt

@@ -0,0 +1,21 @@
+:i argc 0
+:b stdin 0
+
+:i returncode 1
+:b stdout 209
+Perfect square: 100
+Perfect square: 81
+Perfect square: 64
+Perfect square: 49
+Perfect square: 36
+Perfect square: 25
+Perfect square: 16
+Perfect square: 9
+Perfect square: 4
+Perfect square: 1
+Perfect square: 0
+-1
+
+:b stderr 89
+
+Value error, input: ./examples/whole-sqrt.porth:22:5 Can't get sqrt from negative number