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dev:crosscompiler:strings

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dev:crosscompiler:strings [2015/04/06 16:14] – [Erzeugung] ursgrafdev:crosscompiler:strings [2015/04/18 08:42] – [Constant String] ursgraf
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 The field //size// holds the number of bytes of the whole object. This is analogous to other objects (see [[dev:rts:heap|Heap Manager and Garbage Collection]]). It is used for an efficient sweep phase. The field //size// holds the number of bytes of the whole object. This is analogous to other objects (see [[dev:rts:heap|Heap Manager and Garbage Collection]]). It is used for an efficient sweep phase.
  
-===== Erzeugung =====+===== Creation =====
 The Bytecode for the creation of a string is The Bytecode for the creation of a string is
 <code> <code>
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   * initialize the string.   * initialize the string.
 Finally, the reference to the newly created string has to be put into the result register of the //sCnew// instruction.   Finally, the reference to the newly created string has to be put into the result register of the //sCnew// instruction.  
-===== Feldzugriffe ===== +===== Access to Fields ===== 
-Sobald auf Felder des Stringarrays zugegriffen werden soll, muss das im Codegenerator speziell berücksichtigt werden. Ein solcher Zugriff hat in der SSA die Form+When accessing fields of a string, the code generator has to modify the code. Such an access shows up in the SSA as follows
 <code> <code>
 1: MonadicRef[sCloadFromField] {0} <value([C)> (Char-Array) 1: MonadicRef[sCloadFromField] {0} <value([C)> (Char-Array)
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 3: Dyadic[sCloadFromArray] {1, 2} (Char) 3: Dyadic[sCloadFromArray] {1, 2} (Char)
 </code> </code>
-Zuerst wird also das Feld //value// geladen. //value// ist eine Referenz. Anschliessend wird über die Referenz und ein Index auf das Array zugegriffen. Im Codegenerator muss bei einer Instruktion //sCloadFromField// geprüft werden, ob auf das Feld //String.value// zugegriffen wird. Falls ja, wird dieser Zugriff weggelassen und der Offset von //value// gemerkt. Bei der darauffolgenden Instruktion //sCloadFromArray// muss dieser Offset zum Index dazuaddiert werden. Ebenfalls darf als Arrayreferenz nicht das //value// dienen, sondern die Referenz auf den String. \\ +The field //value// is loaded. //value// is a reference. With this reference and an index into the array the proper character can be accessed. The code generator has to check for the instruction //sCloadFromField// if the field is  //String.value//. If true, the fetching is ommited and the offset of //value// is stored. With the subsequent instruction //sCloadFromArray//, the offset must be added to the index. At the same time one cannot use //value// as the array reference but must use the reference to the string. \\ 
-Analog muss auch das Schreiben auf die Stringzeichen angepasst werden. Hier gibt es aber noch eine Besonderheit. Weil Strings immutable sind, werden nur beim Initialisieren in den Fabrikmethoden die Arrayfelder geschrieben. Darum kann die Prüfung auf Arrayüberschreitung weggelassen werden.+Similarly, writing to a string must be customized. However, strings in java are immutable. Writing to strings happens only in the factory methods during initialization. Checking for array index out of bounds may be ommited as well.
  
 ===== Constant String ===== ===== Constant String =====
-Constant strings are stored in the constant block of a class, see [[Linker32]]. The layout there must be identical to the layout on the heap as given above.+Constant strings are stored in the constant block of a class, see [[dev:crosscompiler:backend_ppc:linker32|Linker32]]. The layout there must be identical to the layout on the heap as given above.
  
 ===== Special Linking ===== ===== Special Linking =====
 The type descriptor of the class //String// must have its field //nofInstPtr// set to 0. Though there is a field //char[] values// we access this field in an omtimized way as decribed above. The garbage collector must not follow this field! The type descriptor of the class //String// must have its field //nofInstPtr// set to 0. Though there is a field //char[] values// we access this field in an omtimized way as decribed above. The garbage collector must not follow this field!
dev/crosscompiler/strings.txt · Last modified: 2016/02/25 13:33 by 127.0.0.1

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