Some basic code questions

[kkobraa]

Hi,

I have some questions below:

Question #1: Is it ok if I declare like the codes below? I will use these values as constants. Or I have to use them as variables to get a float values?

Code:
#define Vref 2.1
#define R_load 0.18
#define Rs 0.036
#define Ts 1e-5
#define L 1e-4

Question #2: Do I need to do right-shift to get the right value of ADC? The sense value of ADC is 2.5V.

Code:
Vsense_adc_read = read_adc(); //10-bit ADC
Vsense_adc_read = Vsense_adc_read>>6; //right-shift
iVsense = (int32)((Vsense_adc_read)*(iADCgain));

Question #3: Is this right?

A = 2.5;
A = A>>13;
B = 3.4;
B = B>>13;
C = (int32)(A*B)>>26;

does it mean that C = 8? What if C is a float variable and the last line of code is: C = (A*B)>>26, then C = 8.5?

I'm new in this.

Thanks alot
Ken.

[PCM programmer]

[kkobraa]

Hi,

Thanks for you reply.
Let me state question #3 again.

Question #3:

Code:

A=2.5; // A is a constant
B = 3.4 // B is a constant
A1 = A*1024; // A1 = A*2^10
B1 = B*1024; // B1 = B*2^10
C1 = int32(A1*B1)>>20; // C1 is int32 variable
C2 = (A1*B1)>>20; //C2 is float variable

The question is: C1=8 and C2=8.5?

The reason I do this is because I don't want to use float variables. I need ROM for other purposes and save time.

Thanks again and any suggest would help.

Ken.

[PCM programmer]

I'm still not completely sure what you want, maybe because of the
way you're writing it.

You didn't show your variable declarations.

What are the data types for A, B, A1, B1, C1 and C2 ?

You said "I don't want to use float variables".

If none of those variables listed above are floats, you'll never
get a value such as 8.5 loaded into them. It will be 8 or 9 or
some other integer.

It's tough to know, but I think you may be asking if the
compiler pre-processor will do floating point math, and then
convert the result to an integer and stuff it into your integer
variable ? Example: