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V0.9: Improve the out of range check in tgt-vhdl/stmt.cc 

Promote the unsigned values to long to get a good comparison and on a
machine where an unsigned is the same size as a long (32 bit) assert
that the unsigned values are constrained to fit into a long. It's unlikely
the values needed to create invalid results would ever happen, but this
patch makes sure it doesn't go undetected.
This commit is contained in:
Cary R 2011-10-25 15:57:05 -07:00 committed by Stephen Williams
parent 17344563a8
commit 0ad589eaca
1 changed files with 12 additions and 2 deletions
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14
tgt-vhdl/stmt.cc
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@ -1,7 +1,7 @@
/*
* VHDL code generation for statements.
*
* Copyright (C) 2008-2009 Nick Gasson (nick@nickg.me.uk)
* Copyright (C) 2008-2011 Nick Gasson (nick@nickg.me.uk)
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@ -1161,6 +1161,15 @@ static bool process_signal(vhdl_binop_expr *all, vhdl_var_ref *test,
}
unsigned ewid = ivl_expr_width(expr);
if (sizeof(unsigned) >= sizeof(long)) {
// Since we will be casting i (constrained by swid) to a long make sure
// it will fit into a long. This is actually off by one, but this is the
// best we can do since on 32 bit machines an unsigned and long are the
// same size.
assert(swid <= static_cast<unsigned>(numeric_limits<long>::max()));
// We are also going to cast ewid to long so check it as well.
assert(ewid <= static_cast<unsigned>(numeric_limits<long>::max()));
}
for (unsigned i = 0; i < swid; i++) {
// Generate a comparison for this bit position
vhdl_binop_expr *cmp;
@ -1170,7 +1179,8 @@ static bool process_signal(vhdl_binop_expr *all, vhdl_var_ref *test,
// Check if this is an out of bounds access. If this is a casez
// then check against a constant 'x' for the out of bound bits
// otherwise skip the check (casex).
if (i + sbase >= ewid || i + sbase < 0) {
if (static_cast<long>(i) + sbase >= static_cast<long>(ewid) ||
static_cast<long>(i) + sbase < 0) {
if (is_casez) {
// Get the current test bit.
type = vhdl_type::nunsigned(width);