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Convert Float to Int using Assembly Language Programming

, 15 Jun 2005
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An article on Converting Float value to an integer value trimming off the decimal part

Introduction

This program takes a floating point value as input and converts it into an integer by trimming the decimal point. Please e-mail your suggestion to Jayadev at jayadevmv@rediffmail.com.

Background

The code uses the tag _asm in VC++. Using the assembly code, the floating point value is converted into an integer value.

Using the Code

The code is very simple and it can be plugged into any other code easily.

The function ftoi looks like this:

int ftoi(float flt)
{
    int i;
    _asm
    {
        mov  eax,flt; //loaded mem to acc
        rcl  eax,1;   //left shift acc to remove the sign
        mov  ebx,eax; //save the acc
        mov  edx,4278190080; //clear reg edx;
        and  eax,edx; //and acc to retrieve the exponent
        shr  eax,24;
        sub  eax,7fh; //subtract 7fh(127) to get the actual power 
        mov  edx,eax; //save acc val power
        mov  eax,ebx; //retrieve from ebx
        rcl  eax,8;     //trim the left 8 bits that contain the power
        mov  ebx,eax; //store
        mov  ecx, 1fh; //subtract 17 h
        sub  ecx,edx; 
        mov  edx,00000000h;
        cmp  ecx,0;
        je   loop2;
        shr  eax,1;
        or   eax,80000000h;        
loop1:    
        shr  eax,1; //shift (total bits - power bits);
        sub  ecx,1;
        add  edx,1;
        cmp  ecx,0;
        ja   loop1;
loop2:  
        mov  i, eax;        
    
//check sign +/-        
sign:
        mov  eax,flt;
        and  eax,80000000h;
        cmp  eax,80000000h;
        je     putsign;
    }

    return i;

putsign:
    return -i;
}

History

  • 15th June, 2005: Initial version

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Jayadev MV
Web Developer
India India
Hi.. I have been working on C/C++ for more than 2 years. My areas of interest are Network programming and System Level programming.
I work with C/C++ over Windows and Solaris.

Comments and Discussions

 
GeneralProblem with conversion of float to int using C++ PinmemberKishore JP3-Mar-08 1:25 
Questionhi why so difficult ? Pinmemberjustme2215-Jun-05 2:00 
Answer2+2 == sqrt(16) PinmemberKochise15-Jun-05 3:11 
I think the author just wanted to trim the mantissa to keep the integer part from a floating point, without having to deals with the FPU...
 
Kochise
 
In Code we trust !
GeneralRe: 2+2 == sqrt(16) PinmemberRick York15-Jun-05 8:11 
AnswerRounding mode PinmemberDon Clugston15-Jun-05 14:29 
GeneralRe: Rounding mode PinmemberJohn M. Drescher15-Jun-05 16:16 
AnswerRe: hi why so difficult ? PinmemberJohn M. Drescher15-Jun-05 16:10 
AnswerRe: hi why so difficult ? PinmemberJeanLuc_17-Sep-09 6:52 

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