commit 030d3b13e22e9aa1af5e76470019c7c0c20323af
Author: Sigma <git@sigma-star.io>
Date:   Tue Sep 17 22:30:15 2024 +0200

    Add brainfuck interpreter

diff --git a/brainfuck.sql b/brainfuck.sql
new file mode 100644
index 0000000..b624cc3
--- /dev/null
+++ b/brainfuck.sql
@@ -0,0 +1,115 @@
+CREATE TABLE input (
+  input text
+);
+
+INSERT INTO input VALUES ('');
+
+CREATE TABLE program (
+  program text
+);
+
+
+INSERT INTO program VALUES ('>++++++++[<+++++++++>-]<.>++++[<+++++++>-]<+.+++++++..+++.>>++++++[<+++++++>-]<+
++.------------.>++++++[<+++++++++>-]<+.<.+++.------.--------.>>>++++[<++++++++>-
+]<+.$');
+
+
+WITH RECURSIVE run_state 
+  (iteration, input, output, band, band_position, program, program_position, halted) AS (
+    SELECT 
+      0,
+      input,
+      ''::text,
+      repeat('\000'::text, 10)::bytea,
+      0,
+      program,
+      1,
+      false
+    FROM input
+    CROSS JOIN program
+    UNION ALL
+    SELECT
+      iteration + 1,
+      CASE
+        WHEN substring(program, program_position, 1) = ',' THEN substring(input from 2)
+        ELSE input
+      END,
+      CASE 
+        WHEN substring(program, program_position, 1) = '.' THEN output || chr(get_byte(band, band_position))
+        ELSE output
+      END,
+      CASE
+        WHEN substring(program, program_position, 1) = ',' THEN set_byte(band, band_position, ascii(substring(input, 1, 1)))
+        WHEN substring(program, program_position, 1) = '+' THEN set_byte(band, band_position, get_byte(band, band_position) + 1)
+        WHEN substring(program, program_position, 1) = '-' THEN set_byte(band, band_position, get_byte(band, band_position) - 1)
+        ELSE band
+      END,
+      CASE
+        WHEN substring(program, program_position, 1) = '<' THEN band_position - 1
+        WHEN substring(program, program_position, 1) = '>' THEN band_position + 1
+        ELSE band_position
+      END,
+      program,
+      CASE
+        WHEN substring(program, program_position, 1) = '[' THEN
+          CASE 
+            WHEN get_byte(band, band_position) = 0 THEN
+              (
+                WITH RECURSIVE forward_search (position, stack, done) AS (
+                  SELECT program_position + 1, 0, false
+                  UNION ALL
+                  SELECT 
+                    position + 1,
+                    CASE
+                      WHEN substring(program, position, 1) = '[' THEN stack + 1
+                      WHEN substring(program, position, 1) = ']' THEN stack - 1
+                      ELSE stack
+                    END,
+                    substring(program, position, 1) = ']' AND stack = 0
+                  FROM forward_search
+                  WHERE NOT done
+                )
+                SELECT position
+                FROM forward_search
+                WHERE done
+              )
+            ELSE program_position + 1
+          END
+        WHEN substring(program, program_position, 1) = ']' THEN
+          CASE
+            WHEN get_byte(band, band_position) = 0 THEN program_position + 1
+            ELSE 
+              (
+                WITH RECURSIVE backward_search (position, stack, done) AS (
+                  SELECT program_position - 1, 0, false
+                  UNION ALL
+                  SELECT 
+                    position - 1,
+                    CASE
+                      WHEN substring(program, position, 1) = ']' THEN stack + 1
+                      WHEN substring(program, position, 1) = '[' THEN stack - 1
+                      ELSE stack
+                    END,
+                    substring(program, position, 1) = '[' AND stack = 0
+                  FROM backward_search
+                  WHERE NOT done
+                )
+                SELECT position + 2
+                FROM backward_search
+                WHERE done
+              )
+          END
+        ELSE program_position + 1
+      END,
+      substring(program, program_position, 1) = '$'
+    FROM run_state
+    WHERE NOT halted
+  )
+SELECT iteration, output
+FROM run_state
+WHERE halted
+
+
+
+
+