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RENESAS TOOL NEWS on March 1, 2006: RSO-M3T-CC32R-060301D
A Note on Using
the C/C++ Compiler Package--M3T-CC32R--
for the M32R Family of MCUs |
Please take note of the following problem in using the C/C++ Compiler
Package--M3T-CC32R--for the M32R family of MCUs:
- On constant expressions of integers containing a shift operator whose right operand is an unsigned integer type
- Versions Concerned
CC32R V.1.00 Release 1--V.5.00 Release 00
- Description
If a constant expression of integers contains a left- or right-shift
operation whose right operand (a shift count) is an unsigned integer
type, any of the following problems arises according to what the
constant expression specifies. Note, however, that if you compile
programs in C++ language mode using the CC32R V.5.00 Release 00,
those problems will not arise:
| (1) |
|
When a constant expression specifies the size of a member of
a bit field (as shown in Example 1 in Section 3), an incorrect
size is assumed to be the correct one, which provides the
following warning message:
Warning message:
"xxxx", line XX: warning: shift count greater than number of bits
Here, xxxx denotes the name of a source file, and XX does the
number of the line where the constant expression is placed.
|
| (2) |
|
When a constant expression specifies the size of an array
(as shown in Example 2 in Section 3), an error arises which
provides the following error message as well as the warning
message in (1) above:
error: array: subscript must be positive, non-zero, integral value |
| (3) |
|
When a constant expression specifies the value of an enumeration
constant (as shown in Example 3 in Section 3), an error arises
which provides the following error message as well as the warning
message in (1) above:
error: enumeration-constant out of range |
| (4) |
|
When a constant expression is used as the integer constant
expression of a case label (as shown in Example 4 in Section 3),
an error arises which provides the following error message as
well as the warning message in (1) above:
error: unable to evaluate case label (out of range?) |
| (5) |
|
When a constant expression is used in the other cases (for
example, as shown in Example 5 in Section 3), compilation
is properly performed but the warning message in (1) above
appears.
|
- Conditions
The above problems occur if the following conditions are both
satisfied:
| (1) |
|
In a program exists an constant expression of integers that
contains a left- or right-shift operation. |
| (2) |
|
The right operand (a shift count) of the shift operation in (1)
is an unsigned integer type. |
Examples:
-------------------------------------------------------------
struct SBtag {
short b01:1<<(unsigned)2; /* Example 1 */
short b02:1;
};
int array[8>>1u]; /* Example 2 */
enum Etag {
A,
B = 2<<(unsigned)2 /* Example 3 */
};
int func3(int key)
{
switch (key) {
case ((3*8)>>(7UL-5)): /* Example 4 */
return 1;
}
return 0;
}
int data = 0x8000>>12u; /* Example 5 */
-------------------------------------------------------------
- Workarounds
The above problems can be circumvented either of the following ways:
| (1) |
|
Cast the right operand of a shift operation to the signed integer
type; for example, convert its type using the type cast operator
(signed) as shown in Example below.
Example:
-----------------------------------------------------------------------
struct SBtag {
short b01:1<<(signed)(unsigned)2;/* Right operand cast by (signed) */
short b02:1;
};
int array[8>>(signed)1u]; /* Right operand cast by (signed) */
enum Etag {
A,
B = 2<<(signed)(unsigned)2 /* Right operand cast by (signed) */
};
int func3(int key)
{
switch (key) {
case ((3*8)>>(signed)(7UL-5)): /* Right operand cast by (signed) */
return 1;
}
return 0;
}
int data = 0x8000>>(signed)12u; /* Right operand cast by (signed) */
----------------------------------------------------------------------- |
| (2) |
|
In the M3T-CC32R V.5.00 Release 00, compile the program in C++
language mode; that is, place extern "C" immediately before the
original C source program and enclose the program in braces { } as
shown below (this change must be made to file by file), and then
compile it using the -lang=cpp option.
--------------------
extern "C" {
. . . . . . . . .
(Original C source program)
. . . . . . . . .
}
--------------------
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- Schedule of Fixing the Problem
We plan to fix this problem in the next release of the product.
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