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

[Andrew C Aitchison]

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.
>>

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