stringto 64 - Forums - ASM Community

how would i convert a string(number), into a 64bit varable stored in eax and ebx?

Posted on 2004-09-19 19:58:38 by Qages

As you probably know, there may be 1001 ways to achieve that in assembler. One of them could be with the FPU as follows (you should add error checking for unacceptable characters and/or overflow if intended for use by others than yourself):

str2qw proc public lpsrc:DWORD

LOCAL   units    :DWORD

LOCAL   ten      :DWORD

LOCAL   answer   :QWORD

   mov  ten,10

   finit

   fldz             ;initialize top FPU register

   push esi

   mov  esi,lpsrc

   xor  eax,eax

loop1:

   lodsb

   or   al,al

   jz   finish      ;reached end of string

   sub  al,30h      ;convert from ASCII to binary

   mov  units,eax

   fimul ten

   fiadd units

   jmp  loop1

finish:

   fistp answer     ;store answer in memory

   lea  esi,answer

   mov  eax,[esi]   ;LS dword in EAX

   mov  ebx,[esi+4] ;MS dword in EBX

   pop  esi

   ret

srt2qw endp

Raymond

Posted on 2004-09-19 22:06:00 by Raymond

stringto 64

Hi...

It is not bad your code...You wrote it to show how to use FPU instructions...it is true that not a lot of persons use them...

For my own I find your code too long in time...

and the better way to multiply by 10 is...



mov ebx,eax

shl ebx,1                 ; x 2

shl eax,3                 ; x 8  

add eax,ecx               ; 2+8 =10

And like that you can confim your adage...

Gerard...
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Posted on 2004-09-20 00:40:31 by gerard

stringto 64

You meant



mov ebx,eax

shl ebx,1                 ; x 2

shl eax,3                 ; x 8 

add eax,ebx               ; 2+8 =10

I guess..

Posted on 2004-09-20 07:24:09 by roticv

stringto 64

gerard

An even better way to multiply by 10 is:

shl  eax,1

lea  eax,[eax+eax*4]

However, this thread is to convert a string to a qword. At some point, the partial sum may exceed 32 bits and reside in 2 registers if the FPU is not used. Although multiplying it by 10 is still possible, it would be somewhat more complicated than the above code or yours.

Raymond

Posted on 2004-09-20 10:13:36 by Raymond