-- File DBStorageString.mesa -- Last edited by MBrown on 20-Jun-81 16:14:59 DIRECTORY DBStorageTID USING[TID], DBStorageVec USING[SlotIndexField, VecHeader, LengthField]; DBStorageString: DEFINITIONS = BEGIN OPEN DBStorageTID; -- This interface contains the internal storage level definitions that relate to the --representation of VarByte (and VarWord) fields. IString: TYPE = MACHINE DEPENDENT RECORD[ bytesInString: DBStorageVec.LengthField, -- length, in bytes, of string stored in text portion of InlineString. slotOfExtension: DBStorageVec.SlotIndexField, -- zero means no extension (whole string fits into text field) -- nonzero is slot number of an LString. rest: SELECT OVERLAID * FROM word => [words: ARRAY [0..0) OF WORD _ NULL], text => [text: PACKED ARRAY [0..0) OF CHARACTER _ NULL], ENDCASE ];--IString -- This is the portion of a variable length field (VarByte or VarWord) that is stored --in the tuple body. The text portion allows space to be reserved in the tuple body --for the "expected" length of the field. The actual amount of space for text in an --IString is not represented anywhere in the tuple body, but is kept in the field --handle that is used for all accesses to this field. SizeOfNullIString: CARDINAL = SIZE[IString]; LString: TYPE = MACHINE DEPENDENT RECORD[ header: DBStorageVec.VecHeader, -- LString is stored in a vec, so prefix is a VecHeader bytesInRemString: CARDINAL, -- length of string represented by this LString (so storage allocation can be done --all at once). eStringID: TID -- ID of a "tuple" on another page; this tuple holds the first chars from --remainder of string. Can't be null. ];--LString SizeOfNullLString: CARDINAL = SIZE[LString]; EString: TYPE = MACHINE DEPENDENT RECORD[ header: DBStorageVec.VecHeader, -- EString is stored in a vec, so prefix is a VecHeader eStringID: TID, -- ID of a "tuple" on another page; this tuple holds the first chars from --remainder of string. Null => this tuple holds tail of string. rest: SELECT OVERLAID * FROM word => [words: ARRAY [0..0) OF WORD _ NULL], text => [text: PACKED ARRAY [0..0) OF CHARACTER _ NULL], ENDCASE ];--EString SizeOfNullEString: CARDINAL = SIZE[EString]; END.--DBStorageString CHANGE LOG Created by MBrown on August 12, 1980 11:03 AM Changed by MBrown on 20-Jun-81 16:14:07 -- use overlaid variants to view variable part of records as words or bytes.