Update to use a more efficient power of 2 check. (#274)

src/pal/pal.h

@@ -76,8 +76,7 @@ namespace snmalloc
   static constexpr size_t OS_PAGE_SIZE = Pal::page_size;
 
   static_assert(
-    bits::next_pow2_const(OS_PAGE_SIZE) == OS_PAGE_SIZE,
-    "OS_PAGE_SIZE must be a power of two");
+    bits::is_pow2(OS_PAGE_SIZE), "OS_PAGE_SIZE must be a power of two");
   static_assert(
     OS_PAGE_SIZE % Aal::smallest_page_size == 0,
     "The smallest architectural page size must divide OS_PAGE_SIZE");

src/pal/pal_bsd_aligned.h

@@ -32,7 +32,7 @@ namespace snmalloc
     static void* reserve_aligned(size_t size) noexcept
     {
       // Alignment must be a power of 2.
-      SNMALLOC_ASSERT(size == bits::next_pow2(size));
+      SNMALLOC_ASSERT(bits::is_pow2(size));
       SNMALLOC_ASSERT(size >= minimum_alloc_size);
 
       size_t log2align = bits::next_pow2_bits(size);

src/pal/pal_freebsd_kernel.h

@@ -62,7 +62,7 @@ namespace snmalloc
     template<bool committed>
     static void* reserve_aligned(size_t size) noexcept
     {
-      SNMALLOC_ASSERT(size == bits::next_pow2(size));
+      SNMALLOC_ASSERT(bits::is_pow2(size));
       SNMALLOC_ASSERT(size >= minimum_alloc_size);
       size_t align = size;
 

src/pal/pal_posix.h

@@ -212,7 +212,7 @@ namespace snmalloc
      */
     static std::pair<void*, size_t> reserve_at_least(size_t size) noexcept
     {
-      SNMALLOC_ASSERT(size == bits::next_pow2(size));
+      SNMALLOC_ASSERT(bits::is_pow2(size));
 
       // Magic number for over-allocating chosen by the Pal
       // These should be further refined based on experiments.

src/pal/pal_windows.h

@@ -185,7 +185,7 @@ namespace snmalloc
     template<bool committed>
     static void* reserve_aligned(size_t size) noexcept
     {
-      SNMALLOC_ASSERT(size == bits::next_pow2(size));
+      SNMALLOC_ASSERT(bits::is_pow2(size));
       SNMALLOC_ASSERT(size >= minimum_alloc_size);
 
       DWORD flags = MEM_RESERVE;
@@ -215,7 +215,7 @@ namespace snmalloc
 #  else
     static std::pair<void*, size_t> reserve_at_least(size_t size) noexcept
     {
-      SNMALLOC_ASSERT(size == bits::next_pow2(size));
+      SNMALLOC_ASSERT(bits::is_pow2(size));
 
       // Magic number for over-allocating chosen by the Pal
       // These should be further refined based on experiments.