Assembly Code for base conversion

[gwalia]

I am working on an assembly code that can read a number in base 7, and print it to a base 9 number. The input of the program can be assumed to be a text file with proper base 7 numbers, one on each line.

I have the C code for what im trying to implement, but im unsure how i would go about doing it in assembly...any suggestions or help will be nice. Thank You in advance.

C Code:

#include <stdio.h>

int main(void)
{
  char ch;
  unsigned int value;
  unsigned int power9;
  
  while (fread(&ch, 1, 1, stdin))
  {
    value = 0;
    // if I am here, I read one character, not at EOF
    // and the character is read into ch
    do
    {
      if (ch != '\n') 
      {
        // if I am here, I just read a digit
        value = (value * 7) + (ch - '0');
      }
      else
      {
        // we are now at the end of line, nothing to do
      }
    } while ((ch != '\n') && (fread(&ch, 1, 1, stdin) != 0));
    // if I am here, we have a value read and interpreted
    printf("%u\n",value);
    power9 = 9*9*9*9*9;
    while (power9 > 0) 
    {
      unsigned quotient;

      quotient = value / power9;
      ch = quotient + '0';
      fwrite(&ch, 1, 1, stdout);
      value %= power9;
      power9 /= 9;
    }
    ch = '\n';
    fwrite(&ch, 1, 1, stdout);
  }
}

[redhead]

I've got a question.. why

power9 = 9*9*9*9*9;

instead of:

power9 = 59049; // floor(pow(9,5)), or 9*9*9*9*9

That would save some cyckles, but most of your intelligent compilers will automaticaly sort that out.

With a bit of optimazation, gcc will give you something like this:

.LC0:
	.string	"%u\n"
	.text
	.p2align 4,,15
.globl main
	.type	main, @function
main:
	pushl	%ebp
	movl	%esp, %ebp
	pushl	%edi
	pushl	%esi
	pushl	%ebx
	subl	$28, %esp
	andl	$-16, %esp
	.p2align 4,,15
.L2:
	movl	stdin, %ebx
	movl	$1, %eax
	movl	$1, %ecx
	movl	%eax, 8(%esp)
	leal	-13(%ebp), %edx
	movl	%ecx, 4(%esp)
	movl	%ebx, 12(%esp)
	xorl	%ebx, %ebx
	movl	%edx, (%esp)
	call	fread
	testl	%eax, %eax
	je	.L19
	.p2align 4,,15
.L5:
	movzbl	-13(%ebp), %edx
	cmpb	$10, %dl
	je	.L6
	leal	0(,%ebx,8), %ecx
	movl	stdin, %esi
	movsbl	%dl,%edi
	subl	%ebx, %ecx
	movl	$1, %edx
	leal	-48(%edi,%ecx), %ebx
	movl	%edx, 4(%esp)
	movl	$1, %ecx
	leal	-13(%ebp), %edx
	movl	%esi, 12(%esp)
	movl	%ecx, 8(%esp)
	movl	%edx, (%esp)
	call	fread
	testl	%eax, %eax
	jne	.L5
.L6:
	movl	%ebx, 4(%esp)
	movl	$59049, %esi
	movl	$954437177, %edi
	movl	$.LC0, (%esp)
	call	printf
	.p2align 4,,15
.L15:
	movl	%ebx, %eax
	xorl	%edx, %edx
	movl	stdout, %ecx
	divl	%esi
	movl	%ecx, 12(%esp)
	movl	$1, %ecx
	movl	%ecx, 4(%esp)
	movl	%edx, %ebx
	addb	$48, %al
	movb	%al, -13(%ebp)
	movl	$1, %edx
	movl	%edx, 8(%esp)
	leal	-13(%ebp), %edx
	movl	%edx, (%esp)
	call	fwrite
	movl	%esi, %eax
	mull	%edi
	shrl	%edx
	testl	%edx, %edx
	movl	%edx, %esi
	jne	.L15
	movb	$10, -13(%ebp)
	movl	stdout, %edi
	movl	$1, %esi
	movl	%esi, 8(%esp)
	movl	$1, %ebx
	leal	-13(%ebp), %eax
	movl	%ebx, 4(%esp)
	movl	%edi, 12(%esp)
	movl	%eax, (%esp)
	call	fwrite
	jmp	.L2
.L19:
	leal	-12(%ebp), %esp
	popl	%ebx
	popl	%esi
	popl	%edi
	popl	%ebp
	ret
	.size	main, .-main

Now with hand uptimazation there are a few instructions which could be eliminated, but execution time would probably be unaffected.

[gwalia]

I think what you have replaced 9*9*9*9*9 with is just fine. I am using gdb as my compiler. Also, i dont know if this might help but there are other requirements as well.

Requirements are:

The input of the program can be assumed to be a text file with proper base 7 numbers, one on each line. You can assume each number starts on a line without leading spaces, and ends on a line without trailing spaces. In other words, each number begins on column 0, and is terminated by the linefeed (newline) character (ASCII 10).

The output of the program should be fixed width base 9 numbers. Each number should have exactly 11 digits (including leading zeros).

[gwalia]

Anyone else have any suggestions?

[deutsch]

I am still fairly new to assembly, did C and C++ for awhile.

I couldn't figure how to post a new topic.

Would there be someone who could help me with some
Win32 assembly code ?

Having problems setting a registry key.

Thanks.

[Hamlin]

Deutsch:

Sure. Gimme a little context and I'll be happy to help.

-Carl