From 3f31d25152babb0e48bf25a4d5f289acfc0cb866 Mon Sep 17 00:00:00 2001
From: whiteand <andrewbeletskiy@gmail.com>
Date: Thu, 7 Oct 2021 00:35:22 +0300
Subject: [PATCH 1/3] docs: added example program that reads number from stdin
 and writes if it's a prime number or not

---
 examples/is-prime.porth | 102 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100644 examples/is-prime.porth

diff --git a/examples/is-prime.porth b/examples/is-prime.porth
new file mode 100644
index 00000000..254bf506
--- /dev/null
+++ b/examples/is-prime.porth
@@ -0,0 +1,102 @@
+include "std.porth"
+
+// Probably need to add to standard library.
+// It's useful to have such definition of true, instead of 
+// `macro true 1 end`
+// because it will allow appropriate typechecking
+macro true
+  0 0 =
+end
+
+macro false
+  0 0 !=
+end
+
+macro divisible
+  % 0 =
+end
+
+// memory 
+// 0 => 11 bytes for chars of the number
+// 11 => result number (8 bytes)
+// 19 => 
+
+macro CHAR_CAPACITY 11 end
+macro CHARS_PTR mem end
+macro DIGITS_LEN_PTR CHARS_PTR CHAR_CAPACITY + end
+macro NUM_PTR DIGITS_LEN_PTR 1 + end
+macro FREE_SPACE NUM_PTR 8 + end
+
+// digit on the stack
+macro increase_digits_len
+    drop
+    DIGITS_LEN_PTR DIGITS_LEN_PTR , 1 + .
+end
+
+macro digits_to_number
+    CHARS_PTR swap while dup 1 > do
+        swap dup , // read char
+        '0' -
+        // dig bool
+        dup 0 >= over 10 < band if
+            NUM_PTR ,64 10 * + NUM_PTR swap .64
+            1 + swap 1 - 
+        else 
+            drop
+            1 + swap dup - 
+        end
+    end drop drop
+end
+
+// returns number read from stdint
+macro read_number
+    NUM_PTR 0 .64
+    DIGITS_LEN_PTR 0 .64
+    CHAR_CAPACITY CHARS_PTR stdin read
+    dup 0 <= if
+        "ERROR: could not read your name, sorry ( ._.)\n" stderr write drop
+        1 exit
+    end
+    digits_to_number
+    NUM_PTR ,64
+end
+
+// expects number
+macro is_prime
+    dup 2 = over
+        3 = bor over
+        5 = bor
+    if
+        drop true
+    else
+        dup 2 divisible over 3 divisible bor over 5 divisible bor if
+            
+            drop false
+        else 
+            true swap 5 while over over dup * >= do
+                // RES NUMBER POSSIBLE_DIVIDER
+                over over divisible if
+                    2drop drop false 0 1 
+                    // false 0 1
+                else
+                    2 +
+                end
+                over over dup * >= if
+                    over over divisible if
+                        2drop drop false 0 1 
+                    else
+                        6 +
+                    end
+                end
+            end drop drop
+        end
+    end
+end
+
+"Enter number?\n" stdout write drop
+
+read_number
+
+is_prime
+
+if "It's prime\n" else "It's not a prime\n" end stdout write drop
\ No newline at end of file

From cea1e361ba4f20ff36ff17af1fa2071ec5c268fa Mon Sep 17 00:00:00 2001
From: whiteand <andrewbeletskiy@gmail.com>
Date: Thu, 7 Oct 2021 00:39:30 +0300
Subject: [PATCH 2/3] removed unnecessary code

---
 examples/is-prime.porth | 29 +++++++++--------------------
 1 file changed, 9 insertions(+), 20 deletions(-)

diff --git a/examples/is-prime.porth b/examples/is-prime.porth
index 254bf506..3f94c3d4 100644
--- a/examples/is-prime.porth
+++ b/examples/is-prime.porth
@@ -12,26 +12,10 @@ macro false
   0 0 !=
 end
 
-macro divisible
-  % 0 =
-end
-
-// memory 
-// 0 => 11 bytes for chars of the number
-// 11 => result number (8 bytes)
-// 19 => 
 
 macro CHAR_CAPACITY 11 end
 macro CHARS_PTR mem end
-macro DIGITS_LEN_PTR CHARS_PTR CHAR_CAPACITY + end
-macro NUM_PTR DIGITS_LEN_PTR 1 + end
-macro FREE_SPACE NUM_PTR 8 + end
-
-// digit on the stack
-macro increase_digits_len
-    drop
-    DIGITS_LEN_PTR DIGITS_LEN_PTR , 1 + .
-end
+macro NUM_PTR CHARS_PTR CHAR_CAPACITY + end
 
 macro digits_to_number
     CHARS_PTR swap while dup 1 > do
@@ -51,7 +35,6 @@ end
 // returns number read from stdint
 macro read_number
     NUM_PTR 0 .64
-    DIGITS_LEN_PTR 0 .64
     CHAR_CAPACITY CHARS_PTR stdin read
     dup 0 <= if
         "ERROR: could not read your name, sorry ( ._.)\n" stderr write drop
@@ -61,6 +44,11 @@ macro read_number
     NUM_PTR ,64
 end
 
+macro divisible
+  % 0 =
+end
+
+
 // expects number
 macro is_prime
     dup 2 = over
@@ -70,7 +58,6 @@ macro is_prime
         drop true
     else
         dup 2 divisible over 3 divisible bor over 5 divisible bor if
-            
             drop false
         else 
             true swap 5 while over over dup * >= do
@@ -99,4 +86,6 @@ read_number
 
 is_prime
 
-if "It's prime\n" else "It's not a prime\n" end stdout write drop
\ No newline at end of file
+if "It's prime\n" else "It's not a prime\n" end stdout write drop
+
+// This algorithm works with O(sqrt N)
\ No newline at end of file

From 6e1b6012ce89a13ab5d29ce878d82017bf30ce63 Mon Sep 17 00:00:00 2001
From: whiteand <andrewbeletskiy@gmail.com>
Date: Thu, 7 Oct 2021 00:46:36 +0300
Subject: [PATCH 3/3] removed unnecessary comments. added useful one

---
 examples/is-prime.porth | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/examples/is-prime.porth b/examples/is-prime.porth
index 3f94c3d4..494541d5 100644
--- a/examples/is-prime.porth
+++ b/examples/is-prime.porth
@@ -32,7 +32,7 @@ macro digits_to_number
     end drop drop
 end
 
-// returns number read from stdint
+// returns number read from stdin
 macro read_number
     NUM_PTR 0 .64
     CHAR_CAPACITY CHARS_PTR stdin read
@@ -44,6 +44,7 @@ macro read_number
     NUM_PTR ,64
 end
 
+// expects number divisor
 macro divisible
   % 0 =
 end
@@ -61,10 +62,8 @@ macro is_prime
             drop false
         else 
             true swap 5 while over over dup * >= do
-                // RES NUMBER POSSIBLE_DIVIDER
                 over over divisible if
                     2drop drop false 0 1 
-                    // false 0 1
                 else
                     2 +
                 end