Warnings in Xcode 4

[adonoho]

Gentlefolk,

Xcode 4/clang, as well as Xcode 3.*/gcc, issues 3 warnings when compiling nameprep.c, toxxx.c and util.c.

Here is one of the warnings:

/Users/awd/Projects/Chatter/ChatterX4/../../Libraries/IFUnicodeURL/IFUnicodeURL/IDNSDK/nameprep.c:76:14:{76:7-76:13}{76:16-76:17}: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare,2]
if (offset < 0 || offset > *length) {return;}
~~~~~~ ^ ~

/Users/awd/Projects/Chatter/ChatterX4/../../Libraries/IFUnicodeURL/IFUnicodeURL/IDNSDK/toxxx.c:192:31:{192:10-192:30}{192:33-192:34}: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare,2]
if ( *(dwzOutputString+i) < 0 || *(dwzOutputString+i) > 0x7F )
~~~~~~~~~~~~~~~~~~~~ ^ ~

There is, of course, a simple fix:

   if (offset > *length) {return;}

Or we could mask out the sign bit:

For nameprep.c:

#define SIZE_T_SIGN_BIT (SIZE_MAX - (SIZE_MAX / 2))

   if ((offset & SIZE_T_SIGN_BIT) || offset > *length) {return;}

For toxxx.c:

#define SIZE_SIGN_BIT (SIZE_MAX - (SIZE_MAX / 2))

    if ( (*(dwzOutputString+i) & SIZE_SIGN_BIT) || *(dwzOutputString+i) > 0x7F )

util.c is a bit harder:

Before:

    if (( c >= 0x0000 && c <= 0x002C ) ||
        (  c == 0x002E || c == 0x002F ) ||
        (  c >= 0x003A && c <= 0x0040 ) ||
        (  c >= 0x005B && c <= 0x0060 ) ||
        (  c >= 0x007B && c <= 0x007F ) )

After:

    if (((!c || c >= 0x0001) && c <= 0x002C ) ||
        (  c == 0x002E       || c == 0x002F ) ||
        (  c >= 0x003A       && c <= 0x0040 ) ||
        (  c >= 0x005B       && c <= 0x0060 ) ||
        (  c >= 0x007B       && c <= 0x007F ) )

Or, even simpler is to turn off tautological warnings ... but I would rather not.

What would be the "right" answer for this project? I've been using the simplest answers, which is to elide the checks on zero, without effect for a long while.

Andrew

[BigZaphod]

That's what I've been doing, too. I just modified my local version of the code to remove the useless conditions. Seemed easiest.

l8r
Sean

On Jul 2, 2011, at 10:42 AM, adonoho wrote:

Gentlefolk,

Xcode 4/clang, as well as Xcode 3.*/gcc, issues 3 warnings when compiling nameprep.c, toxxx.c and util.c.

Here is one of the warnings:

/Users/awd/Projects/Chatter/ChatterX4/../../Libraries/IFUnicodeURL/IFUnicodeURL/IDNSDK/nameprep.c:76:14:{76:7-76:13}{76:16-76:17}: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare,2]
if (offset < 0 || offset > *length) {return;}
~~~~~~ ^ ~

/Users/awd/Projects/Chatter/ChatterX4/../../Libraries/IFUnicodeURL/IFUnicodeURL/IDNSDK/toxxx.c:192:31:{192:10-192:30}{192:33-192:34}: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare,2]
if ( *(dwzOutputString+i) < 0 || *(dwzOutputString+i) > 0x7F )
~~~~~~~~~~~~~~~~~~~~ ^ ~

There is, of course, a simple fix:

  if (offset > *length) {return;}

Or we could mask out the sign bit:

For nameprep.c:

#define SIZE_T_SIGN_BIT (SIZE_MAX - (SIZE_MAX / 2))

  if ((offset & SIZE_T_SIGN_BIT) || offset > *length) {return;}

For toxxx.c:

#define SIZE_SIGN_BIT (SIZE_MAX - (SIZE_MAX / 2))

   if ( (*(dwzOutputString+i) & SIZE_SIGN_BIT) || *(dwzOutputString+i) > 0x7F )

util.c is a bit harder:

Before:

   if (( c >= 0x0000 && c <= 0x002C ) ||
       (  c == 0x002E || c == 0x002F ) ||
       (  c >= 0x003A && c <= 0x0040 ) ||
       (  c >= 0x005B && c <= 0x0060 ) ||
       (  c >= 0x007B && c <= 0x007F ) )

After:

   if (((!c || c >= 0x0001) && c <= 0x002C ) ||
       (  c == 0x002E       || c == 0x002F ) ||
       (  c >= 0x003A       && c <= 0x0040 ) ||
       (  c >= 0x005B       && c <= 0x0060 ) ||
       (  c >= 0x007B       && c <= 0x007F ) )

Or, even simpler is to turn off tautological warnings ... but I would rather not.

What would be the "right" answer for this project? I've been using the simplest answers, which is to elide the checks on zero, without effect for a long while.

Andrew

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