Re: [PATCH 4/6] Add macros for increasing data alignment

["Måns Rullgård" <mans@mansr.com>]

Eric Wong <normalperson@yhbt.net> writes:

> Måns Rullgård <mans@mansr.com> wrote:
>> Eric Wong <normalperson@yhbt.net> writes:
>> >  dnl Checks for library functions.
>> > -AC_CHECK_FUNCS(strcasecmp strdup popen vsnprintf gettimeofday mkstemp fmemopen aligned_alloc)
>> > +AC_CHECK_FUNCS(strcasecmp strdup popen vsnprintf gettimeofday mkstemp fmemopen)
>> > +
>> > +dnl aligned alloc required for sdm using AVX (32-byte) or SSE2 (16-byte)
>> > +AC_CHECK_FUNCS(aligned_alloc)
>> > +AS_IF([test "x$ac_cv_func_aligned_alloc" != xyes], [
>> > +	AC_CHECK_FUNCS([memalign])
>> > +	AS_IF([test "x$ac_cv_func_memalign" != xyes], [
>> > +		AC_CHECK_FUNCS([posix_memalign])
>> > +	])
>> > +])
>> 
>> Why don't you just add (posix_)memalign to the existing list of
>> functions?  It's not an error if some of them don't exist, and you're
>> checking the resulting HAVE_ macros in the same order anyway.
>
> I wanted to avoid the overhead of checking redundantly if one
> function was already available; but perhaps it's not worth the effort
> since `configure' is already slow in other places.

The difference in time is barely noticeable on a modern system.

>> > +static inline void *sox_aligned_alloc_m(size_t align, size_t size)
>> > +{
>> > +  void *res = malloc(align + size + sizeof(void *));
>> > +  char *aligned = (char *)res + align + sizeof(void *);
>> > +
>> > +  aligned -= ((size_t)aligned & (align - 1));
>> 
>> Use uintptr_t rather than size_t there.  Although they are usually the
>> same underlying type, there is no such guarantee, especially for systems
>> bizarre enough not to have an aligned allocation function.
>
> I wanted to, but I figure systems missing *memalign could also
> be missing uintptr_t and stdint.h
> Perhaps "unsigned long" is better?

In that case size_t should be the safe choice.  It's more likely than
unsigned long to be the same size as a pointer.  Of course it doesn't
really matter what size it is since we only care about the low 5 bits,
but the compiler doesn't know that.

-- 
Måns Rullgård

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