fix internal interpretation of negative number literals

- detect and forbid non-positive size casts
- detect and forbid negative struct pattern literal indices
- avoid invalid constant folding of negative based literals

CHANGELOG.md

+## Unreleased
+
+* Non-positive integer size casts are now detected and forbidden
+* Negative indices in struct pattern literals are now detected and forbidden
+
 ## v0.0.8
 
 Future releases will have complete change logs.

src/Convert/Cast.hs

@@ -110,12 +110,17 @@ traverseExprM other =
     traverseSinglyNestedExprsM traverseExprM other
 
 convertCastM :: Expr -> Expr -> Bool -> SC Expr
+convertCastM (Number size) _ _
+    | maybeInt == Nothing = illegal "an integer"
+    | int <= 0            = illegal "a positive integer"
+    where
+        maybeInt = numberToInteger size
+        Just int = maybeInt
+        illegal s = error $ "size cast width " ++ show size ++ " is not " ++ s
 convertCastM (Number size) (Number value) signed =
     return $ Number $
-    case numberToInteger size of
-        Just size' -> numberCast signed (fromIntegral size') value
-        Nothing -> error $ "size cast width " ++ show size
-                        ++ " is not an integer"
+        numberCast signed (fromIntegral size') value
+    where Just size' = numberToInteger size
 convertCastM size value signed = do
     value' <- traverseExprM value
     sizeUsesLocalVars <- embedScopes usesLocalVars size
@@ -177,11 +182,8 @@ castFnName size signed =
     "sv2v_cast_" ++ sizeStr ++ suffix
     where
         sizeStr = case size of
-            Number n ->
-                case numberToInteger n of
-                    Just v -> show v
-                    _ -> error $ "size cast width " ++ show n
-                            ++ " is not an integer"
+            Number n -> show v
+                where Just v = numberToInteger n
             _ -> shortHash size
         suffix = if signed then "_signed" else ""
 

src/Convert/ExprUtils.hs

@@ -177,7 +177,7 @@ pattern NegDec :: Integer -> Expr
 pattern NegDec n <- UniOp UniSub (Dec n)
 
 pattern Bas :: Integer -> Expr
-pattern Bas n <- Number (Based _ _ _ n 0)
+pattern Bas n <- Number (Based _ False _ n 0)
 
 
 -- returns the size of a range

src/Convert/Struct.hs

@@ -229,7 +229,8 @@ convertExpr (struct @ (Struct _ fields [])) (Pattern itemsOrig) =
         isNumbered (Right (Number n)) =
             if maybeIndex == Nothing
                 then error msgNonInteger
-                else index < length fieldNames || error msgOutOfBounds
+                else 0 <= index && index < length fieldNames
+                        || error msgOutOfBounds
             where
                 maybeIndex = fmap fromIntegral $ numberToInteger n
                 Just index = maybeIndex

src/Convert/TypeOf.hs

@@ -128,6 +128,9 @@ traverseExprM other =
 
 -- carry forward the signedness of the expression when cast to the given size
 elaborateSizeCast :: Expr -> Expr -> ST Expr
+elaborateSizeCast (Number size) _ | Just 0 == numberToInteger size =
+    -- special case because zero-width ranges cannot be represented
+    error $ "size cast width " ++ show size ++ " is not a positive integer"
 elaborateSizeCast size value = do
     t <- typeof value
     force <- isStringParam value

src/Language/SystemVerilog/AST/Number.hs

@@ -17,7 +17,7 @@ module Language.SystemVerilog.AST.Number
     , bitToVK
     ) where
 
-import Data.Bits (shiftL)
+import Data.Bits ((.&.), shiftL)
 import Data.Char (digitToInt, intToDigit, toLower)
 import Data.List (elemIndex)
 import Text.Read (readMaybe)
@@ -220,8 +220,13 @@ numberToInteger :: Number -> Maybe Integer
 numberToInteger (UnbasedUnsized Bit1) = Just 1
 numberToInteger (UnbasedUnsized Bit0) = Just 0
 numberToInteger UnbasedUnsized{} = Nothing
-numberToInteger (Decimal _ _ num) = Just num
-numberToInteger (Based _ _ _ num 0) = Just num
+numberToInteger (Decimal sz sg num)
+    | not sg || num .&. pow == 0 = Just num
+    | num == 1                   = Just $ -1
+    | otherwise                  = Just $ negate $ num - pow
+    where pow = 2 ^ (abs sz - 1)
+numberToInteger (Based sz sg _ num 0) =
+    numberToInteger $ Decimal sz sg num
 numberToInteger Based{} = Nothing
 
 -- return the number of bits in a number (i.e. ilog2)

test/core/dimensions.sv

@@ -40,6 +40,10 @@ module top;
 
         $display("args %b", $size(RamPair, 1));
         $display("args %b", $size(RamPair, 1'b1));
+        $display("args %b", $size(RamPair, 1'sb1));
+        $display("args %b", $size(RamPair, 2'sb1));
+        $display("args %b", $size(RamPair, 2'sb01));
+        $display("args %b", $size(RamPair, 2'sb11));
         $display("args %b", $size(RamPair, '1));
         $display("args %b", $size(RamPair, 'o1));
         $display("args %b", $size(RamPair, 1'h1));

test/core/dimensions.v

@@ -37,6 +37,10 @@ module top;
 
         $display("args %b", 2);
         $display("args %b", 2);
+        $display("args %b", 1'bx);
+        $display("args %b", 2);
+        $display("args %b", 2);
+        $display("args %b", 1'bx);
         $display("args %b", 2);
         $display("args %b", 2);
         $display("args %b", 2);

test/error/size_cast_neg_lit_1.sv

+// pattern: size cast width 1'sb1 is not a positive integer
+module top;
+    initial $display((1'sb1)'(2));
+endmodule

test/error/size_cast_neg_lit_2.sv

+// pattern: size cast width 2'sb11 is not a positive integer
+module top;
+    initial $display((2'sb11)'(2));
+endmodule

test/error/size_cast_neg_var_1.sv

+// pattern: size cast width 1'sb1 is not a positive integer
+module top;
+    wire x = 0;
+    initial $display((1'sb1)'(x));
+endmodule

test/error/size_cast_neg_var_2.sv

+// pattern: size cast width 2'sb11 is not a positive integer
+module top;
+    wire x = 0;
+    initial $display((2'sb11)'(x));
+endmodule

test/error/size_cast_x_var.sv

+// pattern: size cast width 1'bx is not an integer
+module top;
+    wire x = 0;
+    initial $display((1'bx)'(x));
+endmodule

test/error/size_cast_zero_lit.sv

+// pattern: size cast width 0 is not a positive integer
+module top;
+    initial $display((0)'(2));
+endmodule

test/error/size_cast_zero_var.sv

+// pattern: size cast width 0 is not a positive integer
+module top;
+    wire x = 0;
+    initial $display((0)'(x));
+endmodule

test/error/struct_out_of_bounds_neg.sv

+// pattern: pattern index -1 is out of bounds for struct packed \{..logic x;.\}
+module top;
+    struct packed {
+        logic x;
+    } s = '{ 1'sb1: 1 };
+endmodule