gistfile1.rb

GC_DEBUG = false

CHAR_BIT = 8
BITS_SIZE = 8
BITS_BITLENGTH = BITS_SIZE * CHAR_BIT
SIZEOF_RVALUE = GC_DEBUG ? 56 : 40
SIZEOF_SIZE_T = 8
SIZEOF_STRUCT_HEAP_PAGE_HEADER = 8

def ceildiv(i, mod)
  ((i + mod - 1) / mod).to_i
end

HEAP_ALIGN_LOG = 14
HEAP_ALIGN = 1 << HEAP_ALIGN_LOG
HEAP_ALIGN_MASK = ~(~0 << HEAP_ALIGN_LOG)
REQUIRED_SIZE_BY_MALLOC = SIZEOF_SIZE_T * 5
HEAP_SIZE = HEAP_ALIGN - REQUIRED_SIZE_BY_MALLOC
HEAP_OBJ_LIMIT = ((HEAP_SIZE - SIZEOF_STRUCT_HEAP_PAGE_HEADER)/SIZEOF_RVALUE).to_i
HEAP_BITMAP_LIMIT = ceildiv(ceildiv(HEAP_SIZE, SIZEOF_RVALUE), BITS_BITLENGTH)
HEAP_BITMAP_SIZE = (BITS_SIZE * HEAP_BITMAP_LIMIT)
HEAP_BITMAP_PLANES = 3

def num_in_page(p)
  ((p & HEAP_ALIGN_MASK) / SIZEOF_RVALUE).to_i
end

def bitmap_index(p)
  num_in_page(p) / BITS_BITLENGTH
end

def page_start_limit(page_body)
  start = page_body + SIZEOF_STRUCT_HEAP_PAGE_HEADER
  limit = HEAP_OBJ_LIMIT
  if start % SIZEOF_RVALUE != 0
    delta = SIZEOF_RVALUE - (start % SIZEOF_RVALUE)
    start = start + delta
    limit = ((HEAP_SIZE - (start - page_body))/SIZEOF_RVALUE).to_i
  end
  [ start, limit ]
end

0.step(HEAP_ALIGN, SIZEOF_SIZE_T) do |addr|
  start, limit = page_start_limit(addr)
  nip = num_in_page(start)
  offset = start - nip
  bi = bitmap_index(start)
  sub = start - addr
  p body: addr, start: start, limit: limit, offset: offset if sub == nip
end