Silence -Wstrict-overflow warnings

[orbea]

Silences the following warnings in ibxm-ac/ibxm.c with gcc-7.1.0 and -O3.

gcc -O3 -ansi -pedantic -Wall -g xm2wav.c ibxm.c -o xm2wav
ibxm.c: In function ‘module_load’:
ibxm.c:95:4: warning: assuming signed overflow does not occur when assuming that (X + c) >= X is always true [-Wstrict-overflow]
  if( offset + length > data->length ) {
    ^
ibxm.c:95:4: warning: assuming signed overflow does not occur when assuming that (X + c) >= X is always true [-Wstrict-overflow]
  if( offset + length > data->length ) {
    ^

Please review to make sure my solution is correct, thanks!

[orbea]

@martincameron When you have a chance can you review this PR? Thanks!

[martincameron]

I suppose the warning means that the optimizer has determined that the function is never called with out-of-bounds parameters unless overflow occurs.

Changing the length parameter to "unsigned int" also avoids the warning, would prefer that.

Cheers, Martin

On 20 August 2017 at 14:42, orbea notifications@github.com wrote:

@martincameron https://github.com/martincameron When you have a chance can you review this PR? Thanks!

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[orbea]

Do you mean like this?

diff --git a/ibxm-ac/ibxm.c b/ibxm-ac/ibxm.c
index b7c1786..1a15dd2 100644
--- a/ibxm-ac/ibxm.c
+++ b/ibxm-ac/ibxm.c
@@ -86,7 +86,7 @@ static int log_2( int x ) {
    return y;
 }

-static char* data_ascii( struct data *data, int offset, int length, char *dest ) {
+static char* data_ascii( struct data *data, int offset, unsigned int length, char *dest ) {
    int idx, chr;
    memset( dest, 32, length );
    if( offset > data->length ) {

While that does silence the warnings it creates new ones as well...

ibxm.c: In function ‘data_ascii’:
ibxm.c:95:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if( offset + length > data->length ) {
                      ^
ibxm.c:98:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for( idx = 0; idx < length; idx++ ) {

This PR suffers from the same issue unfortunately...

[martincameron]

I've checked in a fix that seems to do the right thing.

Thanks a lot! Martin

On 22 August 2017 at 23:21, orbea notifications@github.com wrote:

Do you mean like this?

diff --git a/ibxm-ac/ibxm.c b/ibxm-ac/ibxm.c index b7c1786..1a15dd2 100644 --- a/ibxm-ac/ibxm.c +++ b/ibxm-ac/ibxm.c @@ -86,7 +86,7 @@ static int log_2( int x ) { return y; }

-static char data_ascii( struct data data, int offset, int length, char dest ) { +static char data_ascii( struct data data, int offset, unsigned int length, char dest ) { int idx, chr; memset( dest, 32, length ); if( offset > data->length ) {

While that does silence the warnings it creates new ones as well...

ibxm.c: In function ‘data_ascii’: ibxm.c:95:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if( offset + length > data->length ) { ^ ibxm.c:98:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( idx = 0; idx < length; idx++ ) {

This PR suffers from the same issue unfortunately...

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[orbea]

Thanks, but I am still getting a warning here.

gcc -O3 -ansi -pedantic -Wall -g xm2wav.c ibxm.c -o xm2wav
ibxm.c: In function ‘module_load’:
ibxm.c:96:14: warning: assuming signed overflow does not occur when assuming that (X + c) >= X is always true [-Wstrict-overflow]
  if( end < 0 || end > data->length ) {
      ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~

[orbea]

@martincameron, I updated my commit to attempt to correctly silence the last warning. With this I no longer get any warnings with gcc or clang using -O3, -Wall and -Wextra. Can you review this change to see if the solution is correct?

[martincameron]

Hmm. Well, that's because sizeof( int expression ) always returns 4!

This is a difficult warning to silence, I'm currently on GCC6, so I'm going to have to upgrade to GCC7 to reproduce what you're seeing.

Thanks, Martin

On 29 August 2017 at 02:36, orbea notifications@github.com wrote:

@martincameron https://github.com/martincameron, I updated my commit to attempt to correctly silence the last warning. With this I no longer get any warnings with gcc or clang using -O3, -Wall and -Wextra. Can you review this change to see if the solution is correct?

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[orbea]

Alright, thanks for the feedback!

[martincameron]

Hi, I've finally got GCC7 up and running and checked-in a change that seems to silence the warning when compiling with "-O3 -Wall".

Cheers, Martin.

On 30 August 2017 at 22:20, orbea notifications@github.com wrote:

Alright, thanks for the feedback!

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[orbea]

Cheers, it works here too.