Question

我找到了将float转换为int的代码。

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;
}

您是否认为可以编辑此代码以将32 Int转换为float？

如果可以的话，你可以给我一些建议怎么做？

非常感谢你提出的所有建议和答案。

Answer 1

我的建议：

#include <stdio.h>

float itof (int i)
{
    float flt = 0.0;

    _asm
    {
        mov eax, i
        bt eax, 31
        jnc plus

        rcr [flt], 1
        neg eax

        plus:

        mov edx, 0x7F       // Bias

        bsr ebx, eax

        mov ecx, 23
        cmp ebx, ecx
        jbe fit

        // too big:
        sub bl, cl
        mov cl, bl
        shr eax, cl
        setc cl             // to round or not to round
        add eax, ecx
        add edx, ebx
        mov cl, 23

        fit:
        bsr ebx, eax
        btr eax, ebx
        sub cl, bl
        shl eax, cl
        or [flt], eax

        add ebx, edx
        shl ebx, 23
        or [flt], ebx
    }

    return flt;
}

int main ( void )
{
    float flt;
    int i;

    i = 12345678;
//  i = -0x8888888;     // different results, both are right

    flt = (float)i;
    printf("%i  %f\n",i,flt);

    flt = itof (i);
    printf("%i  %f\n",i,flt);

    return 0;
}

将32 int转换为在Assembler中的float

1 个答案: