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RENESAS TOOL NEWS on June 1, 2005: RSO-M3T-NC30WA_1-050601D
A Note on Using the C Compiler Packages
M3T-NC308WA and M3T-NC30WA
--On Using the labs and abs Functions-- |
Please take note of the following problem in using for the M32C series (M3T-NC308WA); and for the M16C series (M3T-NC30WA) of MCUs:
- On using the labs and abs functions
- Versions Concerned
M3T-NC30WA V.1.00 Release 1 ～ V.5.30 Release 02
M3T-NC308WA V.1.00 Release 1 ～ V.5.40 Release 00
- Description
Calculating an absolute value using the labs or abs function may result in an incorrect value being obtained.
- 2.1 Conditions
- This problem occurs if the following conditions are all satisfied:
| (1) |
The standard header file stdlib.h is included. |
| (2) |
The labs or abs function takes an expression as an argument. |
- 2.2 Example
-
--------------------------------------------------------------------
#include <stdlib.h> /* Condition (1) */
unsigned int b=10;
unsigned int a=8;
unsigned int result;
void func(void)
{
result=abs(a - b); /* Condition (2) */
}
--------------------------------------------------------------------
- Workaround
After including stdlib.h, disable the labs macro using preprocessing directive #undef labs or
disable the abs macro using preprocessing directive #undef.
Example:
--------------------------------------------------------------------
#include <stdlib.h>
#undef abs /* Disable abs macro */
unsigned int b=10;
unsigned int a=8;
unsigned int result;
void func(void)
{
result=abs( a-b );
}
--------------------------------------------------------------------
- Schedule of Fixing the Problem
We plan to fix this problem in the next release of the product.
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