Syslinux - Feb 2018 - [PATCH] syslinux/com32: Fix the printing of left zero padded hexadecimals with a leading '0x'.

From: Brett Walker <brett.walker at geometry.com.au>

When printing hexadecimal numbers to a fixed width, padded with leading zeros,
and also having a leading '0x'; the resultant string can be shortened by
up to
two characters if any leading zero padding character required is.

    int hexnum = 0x00001234;

    printf("%08X", hexnum);  // results in 00001234
    printf("%#08X", hexnum); // results in 0x001234

To correct this, the zero padding counting logic needs to use ndigits instead of
nchars.

Signed-off-by: Brett Walker <brett.walker at geometry.com.au>

---

--- ./syslinux/com32/lib/vsnprintf.c.orig
+++ ./syslinux/com32/lib/vsnprintf.c
@@ -126,7 +126,7 @@ format_int(char *q, size_t n, uintmax_t

     /* Emit zero padding */
     if ((flags & (FL_MINUS | FL_ZERO)) == FL_ZERO && width >
ndigits) {
- while (width > nchars) {
+        while (width > ndigits) {
      EMIT('0');
      width--;
  }

On Thu, Feb 08, 2018 at 11:01:21AM +0000, Brett Walker via Syslinux
wrote:
> From: Brett Walker <brett.walker at geometry.com.au>
> 
> When printing hexadecimal numbers to a fixed width, padded with leading
zeros,
> and also having a leading '0x'; the resultant string can be
shortened by up to
> two characters if any leading zero padding character required is.
> 
>     int hexnum = 0x00001234;
> 
>     printf("%08X", hexnum);  // results in 00001234
>     printf("%#08X", hexnum); // results in 0x001234
> 
> To correct this, the zero padding counting logic needs to use ndigits
instead of
> nchars.
No. You asked for at least 8 chars output. You got 8 chars output. If you
want/expect at least 10 chars output, ask for 10 chars.


-- 
MartinS

You are right Martin. I haven't a lot of experience with C/C++.

What I find somewhat confusing is if hexnum is 0xFFFF1234 I would get 10
characters.

I now have a better understanding of printf's operation; the width specifier
is a minimum width specifier.

Thanks for pointing out the noobie mistake. The patch is bad.

Thanks,
Brett

________________________________
From: Syslinux <syslinux-bounces at zytor.com> on behalf of Martin
Str|mberg via Syslinux <syslinux at zytor.com>
Sent: Friday, 9 February 2018 2:19 AM
To: Brett Walker via Syslinux
Subject: Re: [syslinux] [PATCH] syslinux/com32: Fix the printing of left zero
padded hexadecimals with a leading '0x'.

On Thu, Feb 08, 2018 at 11:01:21AM +0000, Brett Walker via Syslinux
wrote:
> From: Brett Walker <brett.walker at geometry.com.au>
>
> When printing hexadecimal numbers to a fixed width, padded with leading
zeros,
> and also having a leading '0x'; the resultant string can be
shortened by up to
> two characters if any leading zero padding character required is.
>
>     int hexnum = 0x00001234;
>
>     printf("%08X", hexnum);  // results in 00001234
>     printf("%#08X", hexnum); // results in 0x001234
>
> To correct this, the zero padding counting logic needs to use ndigits
instead of
> nchars.
No. You asked for at least 8 chars output. You got 8 chars output. If you
want/expect at least 10 chars output, ask for 10 chars.


--
MartinS
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