Dixon factorization, automatic parameters

app/FactorizationUI.hs

@@ -3,7 +3,7 @@ module FactorizationUI (run) where
 import System.Exit (exitSuccess)
 import Utils (askChoice, askNumber)
 import Factorization
-    ( fermatFactorization, pollardPminus1, dixon
+    ( fermatFactorization, pollardPminus1, dixon, dixonDefaultParams
     , gnfsWith, GNFSParams(..), defaultParams
     )
 
@@ -45,13 +45,33 @@ pollardUI = do
 
 dixonUI :: IO ()
 dixonUI = do
+    putStrLn "Dixon"
+    putStrLn "Factors a composite n (not a prime, a perfect square or a prime power)."
+    putStrLn "Practical for n up to roughly 22 digits; 24 digits already takes about a minute."
     n <- askNumber "Enter an integer n > 1:"
-    b <- askNumber "Enter the bound B:"
-    x <- askNumber "Enter the max random integer x:"
 
+    putStrLn "Parameters:"
+    putStrLn "1) Automatic (recommended)"
+    putStrLn "2) Custom"
+    mode <- askChoice 2
+
+    let (autoB, autoX) = dixonDefaultParams n
+    (b, x) <- case mode of
+        1 -> return (autoB, autoX)
+        _ -> do
+            putStrLn ("Automatic values for this n: bound B = " ++ show autoB
+                      ++ ", max x = " ++ show autoX)
+            b' <- askNumber "Enter the bound B:"
+            x' <- askNumber "Enter the max integer x (the search starts at floor(sqrt n) + 1):"
+            return (b', x')
+
+    putStrLn "Running Dixon (this may take a while)..."
     case dixon n b x of
         Left err -> do
             putStrLn ("Error: " ++ err)
+            if mode == 1
+                then putStrLn "Check that n is composite and not a perfect square or a prime power."
+                else return ()
         Right (p, q) -> do
             putStrLn ("n = " ++ show n)
             putStrLn ("p = " ++ show p)