I have to read fixed point numbers either 4 bytes or 8 bytes and the location of the decimal moves for each item (a known location)(scale number)

Is there a library where this is automated? C/C++ is the language of choice

For Example:

This is assuming a scale of 20

```
double toDoublePrecisionFixedPoint(short first,short second,short third,short forth)
{
double d = 0;
int top = (first << 0x10) | (second & 0x0000FFFF);
top/=8;
top >>= 8;
d+=top;
long long a = 0x0;
a = ((long long)second&0x07FF)<< 0x20;
long long t = 0x0;
t = (((long long)third) << 0x10) & 0xFFFF0000;
long long f = 0x0;
f = (((long long) forth)) & 0xFFFF;
long long bottom = a | t | f;
long long maxflag= 0x80000000000;
double dlong = (double)bottom/(double)maxflag;
d += dlong;
return d;
}
```

This is assuming a scale of 15:

```
float toSinglePrecisionFixedPoint (short first, short second)
{
float f;
float dec = ((float)second) / ((float)0x10000);
f = (float)first;
if(f> 0 && dec >0)
f += dec;
else if(f >0 && dec <0)
f += (1 + dec);
else if(f < 0 && dec < 0)
f += dec;
else if(f < 0 && dec >0)
f -= (1 - dec);
else if(f == 0)
f += dec;
return f;
}
void floatToShorts(float f,short*ret)
{
ret[0] = 0x00;
ret[1] = 0x00;
ret[0] = (short)f;
double decimal = 0;
//THIS IS REMOVING THE WHOLE NUMBER
modf(f , &decimal);
ret[1] = (short)(decimal * 0x10000);
}
void doubleToShorts(double d,short*ret)
{
ret[0] = 0x00;
ret[1] = 0x00;
ret[2] = 0x00;
ret[3] = 0x00;
d*=0x80000000000;
long long l = (long long)d;
ret[0] = ((short)((l & 0xFFFF000000000000) >> 48));
ret[1] = ((short)((l & 0x0000FFFF00000000) >> 32));
ret[2] = ((short)((l & 0x00000000FFFF0000) >> 16));
ret[3] = ((short)((l & 0x000000000000FFFF)));
}
```

This was going okay for me until my project now needs a variable scale location. That is fine - but I'm just curious if there is a better way to do this? There must be a full library

This is complicated quickly and I can easily fat finger something making my code not work - I am also sure I am not doing as much error checking as I should be - so curious if there is a library.

Perhaps you need to use a 'bignum' library. Might be overkill but here's one example: GMP

answered on Stack Overflow Feb 15, 2013 by Jay

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