Function _mi_os_alloc_aligned_offset

3rd/mimalloc-2.0.9/src/os.c:851–874

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void* _mi_os_alloc_aligned_offset(size_t size, size_t alignment, size_t offset, bool commit, bool* large, mi_stats_t* tld_stats) {
  mi_assert(offset <= MI_SEGMENT_SIZE);
  mi_assert(offset <= size);
  mi_assert((alignment % _mi_os_page_size()) == 0);
  if (offset > MI_SEGMENT_SIZE) return NULL;
  if (offset == 0) {
    // regular aligned allocation
    return _mi_os_alloc_aligned(size, alignment, commit, large, tld_stats);
  }
  else {
    // overallocate to align at an offset
    const size_t extra = _mi_align_up(offset, alignment) - offset;
    const size_t oversize = size + extra;
    void* start = _mi_os_alloc_aligned(oversize, alignment, commit, large, tld_stats);
    if (start == NULL) return NULL;
    void* p = (uint8_t*)start + extra;
    mi_assert(_mi_is_aligned((uint8_t*)p + offset, alignment));
    // decommit the overallocation at the start
    if (commit && extra > _mi_os_page_size()) {
      _mi_os_decommit(start, extra, tld_stats);
    }
    return p;
  }
}

void _mi_os_free_aligned(void* p, size_t size, size_t alignment, size_t align_offset, bool was_committed, mi_stats_t* tld_stats) {
  mi_assert(align_offset <= MI_SEGMENT_SIZE);