I am trying to do simple math in c using a microcontroller. The C toolset uVision that I have does not have printf scan etc functions.
In any case the code below reads in two parameters p1, p2 from the user over a serial port usig a simple routine GetHexByte () and copies the parameters into p1 and p2 using a couple of union functions for int (16 bit) and long (32 bit).
The results are displaed via a serial port using a simple routine SendASCII (), which displays ascii representation of the results.
if I enter 1234 for p1 and 5678 for p2, I get 00000060 as answer (r1 bytes)
What am I doing wrong ?
Is it not possible to do fixed point math in C ?
if I convert p1, p2 to float then it works as shown below.
==> r1 (int) = (float) p1 * (float)p2);
Can anyone help ?
Thanks.
Bhal
Code is attached below (except for GetHexByte, Disp String and SendAscii) only because they are long and have been working perfectly.
Code follows.......
union FIXTYPE
unsigned int i; //int = 16 bit//changed to unsigned...
unsigned char c[2];
};
union FIXTYPE ic;
union LONGTYPE
{
long l;
unsigned char c[4];
};
union LONGTYPE lc;
---
void main (void) {
---
unsigned int xdata p1,p2;
unsigned long xdata r1;
---
MADSM_DATA_GEN:
SendByte(0x09);DispString ("enter 2 hex char for param p1, p2 \n");
GetHexByte();ic.c[0]=USER_BYTE;GetHexByte();ic.c[1]=USER_BYTE;
p1 = ic.i;
SendAscii (ic.c[0]);SendAscii (ic.c[1]);
SendByte(0x09);
GetHexByte();ic.c[0]=USER_BYTE;GetHexByte();ic.c[1]=USER_BYTE;
p2 = ic.i;
SendAscii (ic.c[0]);SendAscii (ic.c[1]);
r1 = p1 * p2; lc.l = r1;
// p1 = 1234; p2 = 5678;
// r1 = (float)p1 * (float)p2;
// lc.l = (long int)r1;
SendAscii (lc.c[0]);SendAscii (lc.c[1]);SendAscii (lc.c[2]);SendAscii (lc.c[3]);
goto MADSM_DATA_GEN;
}
