 |
|
|
MAEC TOOL NEWS:
MAECT-M3T-NC308WA-020501D
Notes on C Compilers
M3T-NC308WA, M3T-NC30WA, and M3T-NC79WA
|
|---|
Please take note of the following problems in using C compilers (with an assembler and integrated development environment) M3T-NC308WA, M3T-NC30WA, and M3T-NC79WA:
- On testing bit fields in an if construct
- On conditional expressions containing a subtraction
- Problem on Testing Bit Fields in an if Construct
- 1.1 Products and Versions Concerned
- C compiler for the M32C/80 and M16C/80 series MCUs :
- M3T-NC308WA V.2.00 Release 1 -- V.3.10 Release 3
- C compiler for the M16C/60, M16C/30, M16C/20, and M16C/10 series MCUs :
- M3T-NC30WA V.3.20 Release 1 -- V.5.00 Release 1
- C compiler for the 79xx series MCUs :
- M3T-NC79WA V.3.20 Release 1 -- V.4.10 Release 1
- 1.2 Description
- When in the conditional expression of an if construct are included two (or more) expressions that are logically ANDed one another and each of which tests a bit field, incorrect code will be generated.
- 1.3 Conditions
- This problem occurs if the following six conditions are satisfied:
- (1) Optimizing option "-OR" is used along with "-O5" or "-O4".
- (2) Two (or more) expressions testing a bit field (stored in one bit) are included in the conditional expression of an if construct.
- (3) All the expressions in (2) test equality only (with operator "==").
- (4) More than one expression in (2) tests equality between a bit field and an immediate value of 1.
- (5) All the expressions in (2) are logically ANDed one another (with operator &&).
- (6) The program statement of the if construct is non or an unconditional jump.
- 1.4 Example
---------------------------------------------------------------------
struct bitf {
int b0:1;
int b1:1;
int b2:1;
}bit;
int i;
void func1(void){
if((bit.b0 == 1)&&(bit.b2 == 1)){ /* Conditions (2)--(5) */
; /* Conditions (6) */
}else{
i = 1;
}
}
void func2(void){
if((bit.b0 == 1)&&(bit.b2 == 1)){ /* Conditions (2)--(5) */
goto L1; /* Conditions (6) */
}
i = 1;
L1:;
}
----------------------------------------------------------------------
- 1.5 Workaround
- Use option "-Ono_logical_or_combine" (-ONLOC) at compilation.
- 1.6 Schedule of Fixing the Problem
- We plan to fix this problem in our next release.
Notes on C Compilers M3T-NC308WA, M3T-NC30WA, and M3T-NC79WA
MAECT-M3T-NC308WA-020501D
- Problem on conditional expressions containing a subtraction
- 2.1 Product and Version Concerned
- C compiler for the M16C/60, M16C/30, M16C/20, and M16C/10 series MCUs:
- M3T-NC30WA V.5.00 Release 1
- 2.2 Description
- When the result of a subtraction involving one or two variables of type unsigned is compared with 0 in a conditional expression, incorrect code will be generated.
- 2.3 Conditions
- This problem occurs if the following four conditions are satisfied:
- (1) The conditional expression contains a subtraction.
- (2) The combination of minuend and subtrahend in the subtraction above is any of those, a, b, and c, shown below.
| Minuend | Subtrahend |
| a. | Variable | Variable |
| b. | Variable | Immediate value greater than 8 |
| c. | Immediate value | Variable |
- (3) The variables in (2) are of type unsigned int or unsigned char.
- (4) The result of the subtraction is:
- less than 0 (< 0) or
- less than or equal to 0 (<= 0)
- 2.4 Examples
- In Example 2 below, if the high-order bit is set to 1 by subtracting an immediate value from a variable of type unsigned, the result is interpreted as positive according to the rules of C language. Then, though the less-than-0 condition is always FALSE, it is assumed to be TRUE if the problem arises.
----------------------------------------------------------------------
void func(void)
{
unsigned int i1,i2; /* Condition (3)*/
unsigned char c1; /* Condition (3)*/
// Example 1: The program statement in TRUE executed
i1 = 1;
c1 = 2;
if((i1 - c1) < 0){ /* Conditions (1)--(4)*/
i2 = -1;
}else{
i2 = 1;
}
// Example 2: The program statement in TRUE executed
if((i1 - 10) < 0){ /* Conditions (1)--(4)*/
i2 = -1;
}else{
i2 = 1;
}
// Example 3: The program statement in TRUE executed
i1 = 10;
if((3 - i1) < 0){ /* Conditions (1)--(4)*/
i2 = -1;
}else{
i2 = 1;
}
}
----------------------------------------------------------------------
- 2.5 Workaround
- Cast the unsigned value(s) used in the subtraction in the conditional expression to a signed value.
[Examples]
----------------------------------------------------------------------
void func(void)
{
unsigned int i1,i2;
unsigned char c1;
// Example 1:
i1 = 1;
c1 = 2;
if(((int)i1 - c1) <= 0){ /* Cast to a signed value */
i2 = -1;
}else{
i2 = 1;
}
// Example 2:
if(((int)i1 - 10) <= 0){ /* Cast to a signed value */
i2 = -1;
}else{
i2 = 1;
}
// Example 3:
i1 = 10;
if((3 - (int)i1) <= 0){ /* Cast to a signed value */
i2 = -1;
}else{
i2 = 1;
}
}
----------------------------------------------------------------------
- 2.6 Schedule of Fixing the Problem
- We plan to fix this problem in our next release.
|
|
