Ensure posix_memalign() is never called with bad alignment values

changelog/current.md

@@ -1,4 +1,6 @@
 
 - Fix [rapidyaml#445](https://github.com/biojppm/biojppm/pull/445): Amalgamate: fix include of `<charconv>`.
+- Ensure `posix_memalign()` is never called with bad alignment values ([PR#138](https://github.com/biojppm/c4core/pull/138))
+- Annotate `c4::handle_error()` with `[[noreturn]]` ([PR#137](https://github.com/biojppm/c4core/pull/137))
 - Add `bool from_chars(csubstr s, fmt::overflow_checked_<T> *wrapper)`. There was already is a function receiving `&wrapper`, but `*wrapper` was missing for use with generic code.
 - Update fast_float to v6.1.1 ([PR#136](https://github.com/biojppm/c4core/pull/136))

src/c4/memory_resource.cpp

@@ -38,6 +38,15 @@ void afree_impl(void *ptr)
 
 void* aalloc_impl(size_t size, size_t alignment)
 {
+    // alignment must be nonzero and a power of 2
+    C4_CHECK(alignment > 0 && (alignment & (alignment - 1u)) == 0);
+    // NOTE: alignment needs to be sized in multiples of sizeof(void*)
+    if(C4_UNLIKELY(alignment < sizeof(void*)))
+    {
+        alignment = sizeof(void*);
+    }
+    static_assert((sizeof(void*) & (sizeof(void*)-1u)) == 0, "sizeof(void*) must be a power of 2");
+    C4_CHECK(((alignment & (sizeof(void*) - 1u))) == 0u);
     void *mem;
 #if defined(C4_WIN) || defined(C4_XBOX)
     mem = ::_aligned_malloc(size, alignment);
@@ -48,21 +57,11 @@ void* aalloc_impl(size_t size, size_t alignment)
     mem = memalign(alignment, size);
     C4_CHECK(mem != nullptr || size == 0);
 #elif defined(C4_POSIX) || defined(C4_IOS) || defined(C4_MACOS)
-    // NOTE: alignment needs to be sized in multiples of sizeof(void*)
-    size_t amult = alignment;
-    if(C4_UNLIKELY(alignment < sizeof(void*)))
-    {
-        amult = sizeof(void*);
-    }
-    int ret = ::posix_memalign(&mem, amult, size);
+    int ret = ::posix_memalign(&mem, alignment, size);
     if(C4_UNLIKELY(ret))
     {
-        if(ret == EINVAL)
-        {
-            C4_ERROR("The alignment argument %zu was not a power of two, "
-                     "or was not a multiple of sizeof(void*)", alignment);
-        }
-        else if(ret == ENOMEM)
+        C4_ASSERT(ret != EINVAL); // this was already handled above
+        if(ret == ENOMEM)
         {
             C4_ERROR("There was insufficient memory to fulfill the "
                      "allocation request of %zu bytes (alignment=%lu)", size, size);