We have question about INT16/INT32 multiplication by “-1” but given by minimum negative number:
Is this CPU limitation or compiler error that result value is not changed ?
PS.
In limits.h we have minimum values for 16 bits:
#define SHRT_MIN (-SHRT_MAX-1) /* MIN VALUE FOR SHORT */
#define SHRT_MAX 32767 /* MAX VALUE FOR SHORT */
and for 32 bits:
#define INT_MIN (-INT_MAX-1) /* MIN VALUE FOR INT */
#define INT_MAX 2147483647 /* MAX VALUE FOR INT */
Is this CPU limitation or compiler error that result value is not changed ?
But what result are you expecting?
I hope you can see that the result of val = val * -1 might be unexpected because its value exceeds SHRT_MAX. i.e. -32768 x -1 = 32768 but 32768 is greater than 32767 so the "usual" on-paper result cannot be stored. The question is: what do you expect the CPU to do in this circumstance?
In the case of val = val * (-1); the compiler will use the NEG AX instruction. In the CPU instruction manual, it says that if the initial value is -32768 (0x8000) then the result is unchanged but an overflow is indicated.
So there is no error. The behaviour you see is the behaviour defined by the CPU.
