{"action":"created","comment":{"url":"https://api.github.com/repos/HPI-SWA-Teaching/SWT16-Project-14/pulls/comments/65931900","id":65931900,"diff_hunk":"@@ -0,0 +1,47 @@\n++++\n+date = \"2016-06-06T19:18:21+02:00\"\n+prev = \"/02_imgseg/\"\n+next = \"/_x_resources/\"\n+title = \"Object Headers\"\n+weight = 10\n++++\n+\n+The header of a Squeak object contains of up to three words with the size of 4 bytes.\n+The first is the so called base header and is always present.\n+The second is the full class pointer of the object, it has an offset of -4 and isn't present all the time.\n+The third word is also optional, it has an offset of -8 and contains the size in words of an object.\n+\n+Besides the main information every part of the header contains 2 bit which say, how big the header is.\n+( 0: just the base header is present, 1: the base header and the full class pointer are present, 3: The header contains all three words)\n+\n+Now we need to know which information are stored in the base header:\n+\n+\n+| Bits          | Content                                             |\n+| ------------- |:---------------------------------------------------:|\n+| 0-2           | storage management information                      |\n+| 3-14          | object hash                                         |\n+| 15-19         | compact class index                                 |\n+| 20-23         | object format                                       |\n+| 24-29         | size in words                                       |\n+| 30-31         | header type                                         |\n+\n+The storage management information and the object hash weren't interesting for us.\n+\n+The compact class index is an alternative to the full class pointer of the object if the class is one of 32 special classes ('Compact Classes').\n+\n+The object format gives information about the format of the object. In the table below you can see the meaning of each number:\n+\n+| Number        | Meaning                                             |\n+| ------------- |:---------------------------------------------------:|\n+| 0             |  no fields                                          |\n+| 1             | fixed pointer fields                                |\n+| 2             | indexable pointer fields                            |\n+| 3             | both fixed and indexable pointer fields             |\n+| 4+5           | not used                                            |\n+| 6             | indexable word fields (no pointer)                  |\n+| 7             | not used                                            |\n+| 8-11          | indexable byte fields (no pointers): low 2 bits are low 2 bits of size in bytes |\n+| 12-15         | compiled methods: low 2 bits are low 2 bits of size in bytes. The number of literals is specified in method header, followed by the indexable bytes that store byte codes. |\n+\n+The size in in words stores the objects size if it isn't bigger than 64 words.","path":"notes/content/02_imgseg/object-header.md","position":47,"original_position":47,"commit_id":"99756c8e61f7c138ffea18848f7ee941d06a76d2","original_commit_id":"99756c8e61f7c138ffea18848f7ee941d06a76d2","user":{"login":"TimNN","id":1178249,"avatar_url":"https://avatars.githubusercontent.com/u/1178249?v=3","gravatar_id":"","url":"https://api.github.com/users/TimNN","html_url":"https://github.com/TimNN","followers_url":"https://api.github.com/users/TimNN/followers","following_url":"https://api.github.com/users/TimNN/following{/other_user}","gists_url":"https://api.github.com/users/TimNN/gists{/gist_id}","starred_url":"https://api.github.com/users/TimNN/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/TimNN/subscriptions","organizations_url":"https://api.github.com/users/TimNN/orgs","repos_url":"https://api.github.com/users/TimNN/repos","events_url":"https://api.github.com/users/TimNN/events{/privacy}","received_events_url":"https://api.github.com/users/TimNN/received_events","type":"User","site_admin":false},"body":"Something is wrong with this sentence (\"The size in in words\"), but I don't known what it is supposed to say, so I can't fix 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