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Hi,
I experienced a problem with uint32 calculations.
The following code calculates a wrong result. Has anyone found other problems with the unsigned long integer data type?
xdata unsigned int test1 = 66; xdata unsigned int test2 = 1000; xdata unsigned long int result; int main () { result=(unsigned long int)test1*(unsigned long int)test2; // result is 464 instead of 66000 // it seems that the compiler does the calculation // with 16 bit operations }
The same code works correct when using signed long int.
Your answer is 66*1000 - 65536, so they performed the evaluation using a 16-bit multiplication, loosing the overflow.
The type cast to 32-bit should have had a higher priority than the multiplication so it shouldn't matter if integer promotion was active or not. And even without integer promotion, the right-hand side was 32-bit unsigned even with broken precedence rules, in which case the C language requires that both sides gets promoted to 32-bit unsigned.
Might be time to contact Keil technical support.
Are you using the most current version of the compiler?
Are you sure?
I think the C rules are "int = int * int" then the result is promoted to long. So a cast is required. long = (long)int * int.
The problematic program _does_ contain casts to unsigned long, but the answer shows that the expression was evaluated with 16-bit and not 32-bit numbers.