minimal addition to rewrite bit-vector to character conversion using constant folding.

src/ast/rewriter/char_rewriter.cpp

@@ -0,0 +1,62 @@
+/*++
+Copyright (c) 2015 Microsoft Corporation
+
+Module Name:
+
+    char_rewriter.cpp
+
+Abstract:
+
+    Basic rewriting rules for character constraints
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2015-12-5
+
+--*/
+
+#include "util/debug.h"
+#include "ast/rewriter/char_rewriter.h"
+#include "ast/bv_decl_plugin.h"
+
+char_rewriter::char_rewriter(ast_manager& m):
+    m(m) {
+    m_char = static_cast<char_decl_plugin*>(m.get_plugin(m.mk_family_id("char")));
+}
+
+family_id char_rewriter::get_fid() {
+    return m_char->get_family_id();
+}
+
+br_status char_rewriter::mk_app_core(func_decl * f, unsigned num_args, expr * const * args, expr_ref & result) {
+    SASSERT(f->get_family_id() == get_fid());
+    br_status st = BR_FAILED;
+    switch (f->get_decl_kind()) {
+    case OP_CHAR_CONST:
+        break;
+    case OP_CHAR_LE:
+        break;
+    case OP_CHAR_TO_INT:
+        break;
+    case OP_CHAR_TO_BV:
+        break;
+    case OP_CHAR_FROM_BV:
+        st = mk_char_from_bv(args[0], result);
+        break;
+    case OP_CHAR_IS_DIGIT:
+        break;
+    }
+    return st;
+}
+
+br_status char_rewriter::mk_char_from_bv(expr* e, expr_ref& result) {
+    bv_util bv(m);
+    rational n;
+    if (bv.is_numeral(e, n) && n.is_unsigned()) {
+        if (n > m_char->max_char())
+            return BR_FAILED;
+        result = m_char->mk_char(n.get_unsigned());
+        return BR_DONE;
+    }
+    return BR_FAILED;
+}