Hallo to everyone.
My problem is to have the upper 4 Byte result of a multiply. For example:
unsigned int a=1000000000;//only example value unsigned int b=10000000000; unsigned int c;
the result of a*b = 0x8AC7230489E80000 How to get the upper 4 Bytes: 0x8AC72304 How to get the lower 4 Bytes: 0x89E80000
Can anybody help? I have to programm a super-fast-interrupt-routine for an microcontroller, there is not enough time for floating point.
Define them as long long int (unsigned int if you desire)
long long int a; long long int b; long long int c;
int lower32; int upper32;
c = a * b;
lower32 = *((u32 *) &c); upper32 = *(((u32 *) &c) + 1); // little endian assumed
Don't worry the the last assignments look ugly. The compiler will easily optimize this to a direct 32-bit fetch of the value.
Hello, this is perfect but very slow code...
long long int a; long long int b; long long int c; int lower32; int upper32; c = a * b; lower32 = *((u32 *) &c); upper32 = *(((u32 *) &c) + 1); // little endian assumed
i had to replace u32 by unsigned int :-)
Another side effect: Writing
a=3162277660;// = 0XBC7C871C
gives the result a=0XFFFFFFFFBC7C871C
a=0xBC7C871C;// = 3162277660
gives the result a=0X00000000BC7C871C