iio: tools: Use proper macro to detect _Float16 support

[PATCH] iio: tools: Use proper macro to detect _Float16 support

Posted by Ivan A. Melnikov 6 days, 6 hours ago

__FLT16_MAX__ is an internal compiler macro. GCC defines it if
_Float16 is supported by the target in general, but the support
may depend on the exact target options. For example, on i586
without -msse2 I get the following error from GCC15:

  iio_generic_buffer.c: In function 'print2byte':
  iio_generic_buffer.c:141:17: error: invalid conversion from type '_Float16' without option '-msse2'
    141 |                 printf("%05f ", ((float)converter.f + info->offset) * info->scale);
        |                 ^~~~~~

To fix that, use the public macro without double underscores.

Fixes: cdd445d4b2a9 ("iio: tools: Add support for floating-point types in buffer scan elements")
Signed-off-by: Ivan A. Melnikov <iv@altlinux.org>
---
 tools/iio/iio_generic_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/iio/iio_generic_buffer.c b/tools/iio/iio_generic_buffer.c
index 000193612aad..9ea93984e0e9 100644
--- a/tools/iio/iio_generic_buffer.c
+++ b/tools/iio/iio_generic_buffer.c
@@ -131,7 +131,7 @@ static void print2byte(uint16_t input, struct iio_channel_info *info)
 		printf("%05f ", ((float)input + info->offset) * info->scale);
 		break;
 	case 'f': {
-#if defined(__FLT16_MAX__)
+#if defined(FLT16_MAX)
 		union {
 			uint16_t u;
 			_Float16 f;
-- 
2.50.1

Re: [PATCH] iio: tools: Use proper macro to detect _Float16 support

Posted by Joshua Crofts 5 days, 13 hours ago

On Fri, 18 Sep 2026 20:13:02 +0400
"Ivan A. Melnikov" <iv@altlinux.org> wrote:

> __FLT16_MAX__ is an internal compiler macro. GCC defines it if
> _Float16 is supported by the target in general, but the support
> may depend on the exact target options. For example, on i586
> without -msse2 I get the following error from GCC15:
> 
>   iio_generic_buffer.c: In function 'print2byte':
>   iio_generic_buffer.c:141:17: error: invalid conversion from type '_Float16' without option '-msse2'
>     141 |                 printf("%05f ", ((float)converter.f + info->offset) * info->scale);
>         |                 ^~~~~~
> 
> To fix that, use the public macro without double underscores.
> 
> Fixes: cdd445d4b2a9 ("iio: tools: Add support for floating-point types in buffer scan elements")
> Signed-off-by: Ivan A. Melnikov <iv@altlinux.org>
> ---
>  tools/iio/iio_generic_buffer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/iio/iio_generic_buffer.c b/tools/iio/iio_generic_buffer.c
> index 000193612aad..9ea93984e0e9 100644
> --- a/tools/iio/iio_generic_buffer.c
> +++ b/tools/iio/iio_generic_buffer.c
> @@ -131,7 +131,7 @@ static void print2byte(uint16_t input, struct iio_channel_info *info)
>  		printf("%05f ", ((float)input + info->offset) * info->scale);
>  		break;
>  	case 'f': {
> -#if defined(__FLT16_MAX__)
> +#if defined(FLT16_MAX)
>  		union {
>  			uint16_t u;
>  			_Float16 f;

One Sashiko issue:

Does this unintentionally disable _Float16 support for all architectures?

Since the tools build environment uses gnu11 compilation flags without
explicitly defining __STDC_WANT_IEC_60559_TYPES_EXT__, FLT16_MAX is
undefined across all architectures. This causes the preprocessor to skip
this block entirely, causing the tool to always print 
<unsupported 2-byte float> for 16-bit float data, even on platforms where 
native support previously worked.

If FLT16_MAX were actually defined, the compiler would still parse the
_Float16 block and throw the same missing -msse2 compilation error mentioned
in the commit message. Is there an alternative way to check for hardware
support without completely disabling the feature?

-- 
Kind regards,
Joshua Crofts

Re: [PATCH] iio: tools: Use proper macro to detect _Float16 support

Posted by Ivan A. Melnikov 3 days, 11 hours ago

On Sat, Sep 19, 2026 at 11:39:45AM +0200, Joshua Crofts wrote:
> On Fri, 18 Sep 2026 20:13:02 +0400
> "Ivan A. Melnikov" <iv@altlinux.org> wrote:
> 
> > __FLT16_MAX__ is an internal compiler macro. GCC defines it if
> > _Float16 is supported by the target in general, but the support
> > may depend on the exact target options. For example, on i586
> > without -msse2 I get the following error from GCC15:
> > 
> >   iio_generic_buffer.c: In function 'print2byte':
> >   iio_generic_buffer.c:141:17: error: invalid conversion from type '_Float16' without option '-msse2'
> >     141 |                 printf("%05f ", ((float)converter.f + info->offset) * info->scale);
> >         |                 ^~~~~~
> > 
> > To fix that, use the public macro without double underscores.
> > 
> > Fixes: cdd445d4b2a9 ("iio: tools: Add support for floating-point types in buffer scan elements")
> > Signed-off-by: Ivan A. Melnikov <iv@altlinux.org>
> > ---
> >  tools/iio/iio_generic_buffer.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/tools/iio/iio_generic_buffer.c b/tools/iio/iio_generic_buffer.c
> > index 000193612aad..9ea93984e0e9 100644
> > --- a/tools/iio/iio_generic_buffer.c
> > +++ b/tools/iio/iio_generic_buffer.c
> > @@ -131,7 +131,7 @@ static void print2byte(uint16_t input, struct iio_channel_info *info)
> >  		printf("%05f ", ((float)input + info->offset) * info->scale);
> >  		break;
> >  	case 'f': {
> > -#if defined(__FLT16_MAX__)
> > +#if defined(FLT16_MAX)
> >  		union {
> >  			uint16_t u;
> >  			_Float16 f;
> 
> One Sashiko issue:
> 
> Does this unintentionally disable _Float16 support for all architectures?

Indeed, it does. Sorry, my patch is incorrect. I must have completely
messed up all my checks on Friday.

> Since the tools build environment uses gnu11 compilation flags without
> explicitly defining __STDC_WANT_IEC_60559_TYPES_EXT__, FLT16_MAX is
> undefined across all architectures. This causes the preprocessor to skip
> this block entirely, causing the tool to always print 
> <unsupported 2-byte float> for 16-bit float data, even on platforms where 
> native support previously worked.
> 
> If FLT16_MAX were actually defined, the compiler would still parse the
> _Float16 block and throw the same missing -msse2 compilation error mentioned
> in the commit message. Is there an alternative way to check for hardware
> support without completely disabling the feature?

Apparently, the only correct way to detect _Float16 is to try compiling
some code that uses it. For that, a feature can be added to tools/build.

On other hand, x86 without SSE2 is the only platform I could find where
__FLT16_MAX__ is defined, but _Float16 does not work, so a simple
platform-specific workaround would also work and would be much less
elaborate.

WDYT?

-- 
  wbr,
    iv m.