[gdal-dev] clang-tidy 23 bugprone-signed-bitwise and CPL_LSBINT32PTR macros

[Andrew C Aitchison]

Thanks. That seems fine.
I assume you can do the rest of the family now we have one resolved.

On Mon, 11 May 2026, Even Rouault wrote:

> Please re-try with the latest pushed commit in the PR that should hopefully 
> make -Wsign-conversion happy
>
> Le 11/05/2026 à 14:11, Andrew C Aitchison via gdal-dev a écrit :
>> On Sun, 10 May 2026, Even Rouault wrote:
>> 
>>> Andrew,
>>> 
>>> does https://github.com/OSGeo/gdal/pull/14524 fix the warning?
>> 
>> With that change, clang-tidy is happy, but now the compile breaks if I use
>> `clang++ -Wsign-conversion`:
>> 
>> In file included from /usr/local/gdal/git.llvm/include/gdal_dataset.h:18:
>> /usr/local/gdal/git.llvm/include/cpl_port.h:808:33: error: implicit 
>> conversion changes signedness: 'int' to 'uint32_t' (aka 'unsigned int')
>>       [-Werror,-Wsign-conversion]
>>   808 |         uint32_t unsigned_val = CPL_LSBINT32PTR(x);
>>       |                  ~~~~~~~~~~~~   ^~~~~~~~~~~~~~~~~~
>> /usr/local/gdal/git.llvm/include/cpl_port.h:788:62: note: expanded from 
>> macro
>>       'CPL_LSBINT32PTR'
>>   786 |     ((*CPL_REINTERPRET_CAST(const GByte *, x)) 
>> |                     \
>>       | 
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>   787 |      (*((CPL_REINTERPRET_CAST(const GByte *, x)) + 1) << 8) 
>> |        \
>>       | 
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>   788 |      (*((CPL_REINTERPRET_CAST(const GByte *, x)) + 2) << 16) 
>> |       \
>>       | 
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
>>   789 |      (*((CPL_REINTERPRET_CAST(const GByte *, x)) + 3) << 24))
>>       | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> qed.cpp:122:30: note: in instantiation of function template specialization
>>       'CPL_LSBSINT32PTR<unsigned char>' requested here
>>   122 |     return (static_cast<int>(CPL_LSBSINT32PTR(buf)));
>>       |                              ^
>> 
>> 
>> 
>>> Even
>>> 
>>> Le 10/05/2026 à 16:02, Andrew C Aitchison via gdal-dev a écrit :
>>>> 
>>>> clang-tidy 23 (I'm using Ubuntu 26.04 with build
>>>> ++20260508083129+d791e3a6f4c8-1~exp1~20260508083148.481
>>>> from llvm-toolchain-snapshot at https://www.llvm.org/)
>>>> has a new? check bugprone-signed-bitwise.
>>>> 
>>>> This check objects to macros like CPL_LSBINT32PTR:
>>>> 
>>>> clang-tidy --config="{Checks: 'bugprone-signed-bitwise', CheckOptions: 
>>>> {bugprone-signed-bitwise.IgnorePositiveIntegerLiterals: true}}" 
>>>> frmts/raw/lcpdataset.cpp
>>>> 
>>>> reports 63 warnings of [bugprone-signed-bitwise], starting with:
>>>> 
>>>> /home/werdna/gdal/git/frmts/raw/lcpdataset.cpp:171:10: warning: use of a 
>>>> signed integer operand with a binary bitwise operator 
>>>> [bugprone-signed-bitwise]
>>>>   171 |     if ((CPL_LSBSINT32PTR(poOpenInfo->pabyHeader) != 20 &&
>>>>       |          ^
>>>> /usr/local/gdal/git.llvm/include/cpl_port.h:799:53: note: expanded from 
>>>> macro 'CPL_LSBSINT32PTR'
>>>>   799 | #define CPL_LSBSINT32PTR(x) CPL_STATIC_CAST(GInt32, 
>>>> CPL_LSBINT32PTR(x))
>>>>       | ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
>>>> /usr/local/gdal/git.llvm/include/cpl_port.h:786:6: note: expanded from 
>>>> macro 'CPL_LSBINT32PTR'
>>>>   786 |     ((*CPL_REINTERPRET_CAST(const GByte *, x)) |                  
>>>> \
>>>>       |      ^
>>>>   787 |      (*((CPL_REINTERPRET_CAST(const GByte *, x)) + 1) << 8U) |    
>>>> \
>>>>   788 |      (*((CPL_REINTERPRET_CAST(const GByte *, x)) + 2) << 16U) |   
>>>> \
>>>> |                                                               ~
>>>> /usr/local/gdal/git.llvm/include/cpl_port.h:181:55: note: expanded from 
>>>> macro 'CPL_STATIC_CAST'
>>>>   181 | #define CPL_STATIC_CAST(type, expr) static_cast<type>(expr)
>>>>       | ^~~~
>>>> 
>>>> I suspect that default type-promotion from an unsigned GByte
>>>> to a *signed* int does not help here.
>>>> 
>>>> Not exactly a bug, but annoying.
>>>> 
>> 
>> 
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>
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> http://www.spatialys.com
> My software is free, but my time generally not.
>
>

-- 
Andrew C. Aitchison                      Kendal, UK
                    andrew at aitchison.me.uk