The following content is quoted from:
http://www.esacademy.com/automation/docs/c51primer/c15.htm#15
General Things to be Aware of
The ANSI standard says that the product of two 8 bit numbers is also an 8 bit number. This means that any unsigned chars which might have to be multiplied must actually be declared as unsigned int's if there is any possibility that they may produce even an intermediate result over 255.
However it is very wasteful to use integer quantities in an 8051 if a char can do the job! The solution is to temporarily convert (cast) a char to an int. Here the numerator potentially could be 16 bits but the result always 8 bits. The "(unsigned int)" casts ensure that a 16 bit multiply is used by C51.
{
unsigned char z ;
unsigned char x ;
unsigned char y ;
z = ((unsigned int) y * (unsigned int) x) >> 8 ;
}
Here the two eight bit numbers x and y are multiplied and then divided by 256. The intermediate 16 bit (unsigned int) result is permissible because y and x have been loaded by the multiplier library routine as int's.
