SMV: convert typecasts to SMV

This adds conversion for a variety of typecast expressions into SMV syntax.

Author: kroening

regression/ebmc/smv-word-level/verilog1.desc

@@ -6,7 +6,7 @@ verilog1.sv
 ^INIT main\.x = 0ud32_0$
 ^INVAR Verilog::main\.x_aux0 = main\.x \+ 0ud32_1$
 ^TRANS next\(main\.x\) = Verilog::main\.x_aux0$
-^LTLSPEC F main\.x = 0sd32_10$
+^LTLSPEC F main\.x = unsigned\(0sd32_10\)$
 ^EXIT=0$
 ^SIGNAL=0$
 --

src/smvlang/expr2smv.cpp

@@ -9,6 +9,10 @@ Author: Daniel Kroening, [email protected]
 #include "expr2smv.h"
 #include "expr2smv_class.h"
 
+#include <util/mathematical_types.h>
+
+#include "smv_expr.h"
+
 /*******************************************************************\
 
 Function: expr2smvt::convert_nondet_choice
@@ -221,6 +225,115 @@ expr2smvt::resultt expr2smvt::convert_function_application(
 
 /*******************************************************************\
 
+Function: expr2smvt::convert_typecast
+
+  Inputs:
+
+ Outputs:
+
+ Purpose:
+
+\*******************************************************************/
+
+expr2smvt::resultt expr2smvt::convert_typecast(const typecast_exprt &expr)
+{
+  // typecasts can repesent a variety of functions
+  auto &src_type = expr.op().type();
+  auto &dest_type = expr.type();
+
+  if(src_type.id() == ID_unsignedbv && dest_type.id() == ID_signedbv)
+  {
+    // unsigned to signed
+    auto src_width = to_unsignedbv_type(src_type).get_width();
+    auto dest_width = to_signedbv_type(dest_type).get_width();
+
+    if(src_width == dest_width)
+    {
+      // signess change only
+      return convert_rec(smv_signed_cast_exprt{expr.op(), dest_type});
+    }
+    else if(dest_width > src_width)
+    {
+      // Signedness _and_ width change. First go to signed, then extend.
+      return convert_rec(smv_extend_exprt{
+        smv_signed_cast_exprt{expr.op(), signedbv_typet{src_width}},
+        dest_width - src_width,
+        dest_type});
+    }
+    else
+    {
+      // First shrink, then go signed.
+      return convert_rec(smv_signed_cast_exprt{
+        smv_resize_exprt{expr.op(), dest_width, unsignedbv_typet{dest_width}},
+        dest_type});
+    }
+  }
+  else if(src_type.id() == ID_signedbv && dest_type.id() == ID_unsignedbv)
+  {
+    // signed to unsigned
+    auto src_width = to_signedbv_type(src_type).get_width();
+    auto dest_width = to_unsignedbv_type(dest_type).get_width();
+
+    if(
+      to_signedbv_type(src_type).get_width() ==
+      to_unsignedbv_type(dest_type).get_width())
+    {
+      // signess change only
+      return convert_rec(smv_unsigned_cast_exprt{expr.op(), dest_type});
+    }
+    else if(dest_width > src_width)
+    {
+      // Signedness _and_ width change.
+      // First enlarge, then go unsigned.
+      return convert_rec(smv_unsigned_cast_exprt{
+        smv_extend_exprt{
+          expr.op(), dest_width - src_width, signedbv_typet{dest_width}},
+        dest_type});
+    }
+    else
+    {
+      // First go unsigned, then shrink
+      return convert_rec(smv_resize_exprt{
+        smv_unsigned_cast_exprt{expr.op(), unsignedbv_typet{src_width}},
+        dest_width,
+        dest_type});
+    }
+  }
+  else if(src_type.id() == ID_signedbv && dest_type.id() == ID_signedbv)
+  {
+    // signed to signed, width change.
+    // Note that resize(...) preserves the sign bit, unlike our typecast.
+    auto src_width = to_signedbv_type(src_type).get_width();
+    auto dest_width = to_signedbv_type(dest_type).get_width();
+    if(dest_width > src_width)
+    {
+      return convert_rec(
+        smv_extend_exprt{expr.op(), dest_width - src_width, dest_type});
+    }
+    else
+      return convert_norep(expr);
+  }
+  else if(src_type.id() == ID_unsignedbv && dest_type.id() == ID_unsignedbv)
+  {
+    // Unsigned to unsigned, width change. Use extend when enlarging.
+    auto src_width = to_unsignedbv_type(src_type).get_width();
+    auto dest_width = to_unsignedbv_type(dest_type).get_width();
+    if(dest_width > src_width)
+    {
+      return convert_rec(
+        smv_extend_exprt{expr.op(), dest_width - src_width, dest_type});
+    }
+    else
+    {
+      return convert_rec(smv_resize_exprt{expr.op(), dest_width, dest_type});
+    }
+  }
+  else
+    return convert_norep(expr);
+}
+
+/*******************************************************************\
+
 Function: expr2smvt::convert_rtctl
 
   Inputs:
@@ -713,9 +826,7 @@ expr2smvt::resultt expr2smvt::convert_rec(const exprt &src)
     return convert_function_application("unsigned", src);
 
   else if(src.id() == ID_typecast)
-  {
-    return convert_rec(to_typecast_expr(src).op());
-  }
+    return convert_typecast(to_typecast_expr(src));
 
   else // no SMV language expression for internal representation
     return convert_norep(src);

src/smvlang/expr2smv_class.h

@@ -126,6 +126,8 @@ class expr2smvt
   resultt
   convert_function_application(const std::string &symbol, const exprt &);
 
+  resultt convert_typecast(const typecast_exprt &);
+
   resultt convert_norep(const exprt &);
 };