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how to convert float to int16?

 
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ronnarone.r



Joined: 23 Dec 2008
Posts: 12

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how to convert float to int16?
PostPosted: Sat Mar 13, 2010 6:44 am     Reply with quote

I want to convert float to int16. How to?
SherpaDoug



Joined: 07 Sep 2003
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PostPosted: Sat Mar 13, 2010 7:19 am     Reply with quote

What is wrong with the obvious:

long L;
float F = 12345.6;

L = F;

Should leave L = 12345
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Gavin Pinto



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PostPosted: Sun Mar 14, 2010 9:55 pm     Reply with quote

SherpaDoug wrote:
What is wrong with the obvious:

long L;
float F = 12345.6;

L = F;

Should leave L = 12345


int16 i;

Cast it

i=(int16)F;
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Ttelmah



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PostPosted: Mon Mar 15, 2010 3:42 am     Reply with quote

Both Sherpa Dog's, and Gavin Pinto's answers, do exactly the same thing.
C peforms an automatic 'cast', when variables are assigned to other variables of different types.
Where they would differ, is if you do something 'with' the value on the right of the equation. The explicit cast as shown by Gavin, converts the value 'then and there', into a value of the lower type. The automatic cast, does it at the time the value is put into the variable. Example of the difference:
Code:

float fpval=1234.56;
int16 ival;

ival=fpval; //ival=1234
ival=(int16)fpval; //ival=1234

ival=fpval*2; //ival=2469 - maths is performed using fp arithmetic,
//since 'fpval' is a float value. 1234.56*2 = 2469.12.

ival=(int16)fpval*2; //ival=2468 - the _integer_ 1234, is multipled by two
//using integer arithmetic (faster), giving 2468.....


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Gavin Pinto



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PostPosted: Mon Mar 15, 2010 6:09 pm     Reply with quote

In addition I will show how float is stored. It is stored with 32 bits in memory.

Now look at my demonstration below

Example 1

int buff[10];

int32 *fp;
float F =123.45;
fp = &F;
itoa(*fp,16,buff);
puts(buff);

on hyterminal you will see

66E67685

This is bit pattern in memory.

23 bit mantissa, sign bit, 8 bit exponent with bias of 7F

Example 2

int buff[10];

int32 *fp;
float F =123.45E20;
fp = &F;
itoa(*fp,16,buff);
puts(buff);

on hyterminal you will see

534E27C8

This is bit pattern in memory.

23 bit mantissa, sign bit, 8 bit exponent with bias of 7F



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