Explanation for the basics of datatypes

[patan.gova]

Hello,

I am new to the microcontrollers and want to know the working of the below two functions for the mutliplication of two 16bit numbers, if the 16bit microcontroller is used

Multilication function1
int32_t z; 
z=mutliplication ( 0x1234, 0x5678); 
return  z >> 15;

Multilication function2
signed long z;  
RESLO and RESHI =mutliplication ( 0x1234, 0x5678); //if results are stored in two different variables of 16bits(RESLO=lower,RESHI=higher)
z = RESHI;                          
z = (result<<16)|RESLO;             

Can someone explain me thw working of above lines.

thanks.

 

[paulfjujo]

hello

this is my understanding ...

Multilication function1
int32_t z; 
z=mutliplication ( 0x1234, 0x5678); 
return z >> 15;

Z shifted right 15 times...
i don't know why result of muttiplication is divided by 2^15 (/ 32768)
if you want to get the sign
return z>>31 most significatif bit is the sign 1=Negativ 0 Positive

Multilication function2
signed long z; 
RESLO and RESHI =mutliplication ( 0x1234, 0x5678); //if results are stored in two different variables of 16bits(RESLO=lower,RESHI=higher)
z = RESHI; 
z = (result<<16)|RESLO;

Bad results !

from where do you find "result" variable ?

z =mutliplication ( 0x1234, 0x5678)
RESHI=(int16) ( z>>16);
RESLO=( int16 ) (z & 0x0000FFFF);

 

[patan.gova]

sorry,
I made a mistake while writing and it should be should 'z' instead of 'result' as this
signed long z;
RESLO and RESHI =mutliplication ( 0x1234, 0x5678); //if results are stored in two different variables of 16bits(RESLO=lower,RESHI=higher)
z = RESHI;
z = (z<<16)|RESLO;

 

[patan.gova]

And also which line says so "result of multiplication is divided by 2^15 (/ 32768)