Floating point number handling bug

[kazinoz]

I think there is a bug in the way that LabWindows/CVI handles floating point
numbers, both single and double precision. Double first; the few lines shown
below give a
result = 2.936788244924931 E +194 when the
actual decimal conversion is -48.9121589. (See this conversion page <a href="http://babbage.cs.qc.edu/IEEE-754/64bit.html" target="_blank">http://babbage.cs.qc.edu/IEEE-754/64bit.html</a>).
I have a binary stream coming from a Vector Network Analyser which I can output
in Single Precision Binary(32 bit) &nbsp;or Double precision Binary (64 bit)
(IEEE-754). The line below simplifies the problem from a longer array.

void
main (void)
{
char&nbsp;&nbsp;&nbsp; Input[16] = &quot;C04874C1A0000000&quot;;
double&nbsp;
Result;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Scan(Input, &quot;%s&gt;%f&quot;,
&amp;Result);
}
Following an example I tried the line below. This gave a result
= 2.1738120934444362 E -71 when the actual decimal conversion is
-48.9121589.&nbsp;
void main
(void)
{
char&nbsp;Input[16] =
&quot;C04874C1A0000000&quot;;
double&nbsp;Result;
&nbsp;
&nbsp;Scan(Input, &quot;%1f[z]&gt;%f&quot;,
&amp;Result);
}
&nbsp;
I then tried Single Precision which is actually my desired
format. This gives the result of 1.8364521 E -39 when the actual decimal
conversion is -48.9121589. (See the conversion page
<a href="http://babbage.cs.qc.edu/IEEE-754/32bit.html" target="_blank">http://babbage.cs.qc.edu/IEEE-754/32bit.html</a>)
&nbsp;
void main (void)
{
char&nbsp;Input[8] =
&quot;C243A60D&quot;;
float&nbsp;Result;
&nbsp;
&nbsp;Scan(Input, &quot;%s&gt;%f[b4]&quot;,
&amp;Result);
} &nbsp;If&nbsp; the error of my ways can be explained, I would be grateful.&nbsp;

[jr_2005]

I think you may be expecting more of the Scan function than it is capable of. It would be happy with this conversion:&nbsp;char Input [16] = &quot;-48.9121589&quot;;
float Result;

Scan (Input, &quot;%s&gt;%f&quot;, &amp;Result);
&nbsp;but your ASCII representation of a binary code corresponding to a floating point number will need more manipulation.&nbsp;JR&nbsp;

[ldp]

Hello,&nbsp;a&nbsp;string&nbsp;with&nbsp;hexadecimal&nbsp;digits&nbsp;is&nbsp;not&nbsp;a&nbsp;valid&nbsp;interpretation&nbsp;of&nbsp;a&nbsp;number&nbsp;in&nbsp;ANSI&nbsp;C.&nbsp;It's&nbsp;a&nbsp;mere&nbsp;string.&nbsp;If&nbsp;you&nbsp;have&nbsp;binary data coming in from the vector analyzer, then you can convert each 8-byte group into a double number directly. Example below:unsigned char buffer[]={0x00,0x00,0x00,0xA0,0xC1,0x74,0x48,0xC0}; &nbsp;&nbsp;&nbsp;// Binary representation of double -48.9121589
double *dptr=(double*)buffer; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//&nbsp;Direct&nbsp;conversion&nbsp;to&nbsp;double&nbsp;type&nbsp;&nbsp;The pointer dptr&nbsp;now&nbsp;points to a double value of -48.912158966064453.&nbsp;If your vector analyzer sends the data in text format, you would need to first convert the data to raw&nbsp;binary and&nbsp;then&nbsp;to&nbsp;double.&nbsp;Hope&nbsp;this&nbsp;helps.LDP&nbsp;