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Annotation of 42BSD/ucb/ex/ex_temp.h, revision 1.1

1.1     ! root        1: /* Copyright (c) 1981 Regents of the University of California */
        !             2: /* sccs id:    @(#)ex_temp.h   7.3     8/2/81  */
        !             3: /*
        !             4:  * The editor uses a temporary file for files being edited, in a structure
        !             5:  * similar to that of ed.  The first block of the file is used for a header
        !             6:  * block which guides recovery after editor/system crashes.
        !             7:  * Lines are represented in core by a pointer into the temporary file which
        !             8:  * is packed into 16 bits (32 on VMUNIX).  All but the low bit index the temp
        !             9:  * file; the last is used by global commands.  The parameters below control
        !            10:  * how much the other bits are shifted left before they index the temp file.
        !            11:  * Larger shifts give more slop in the temp file but allow larger files
        !            12:  * to be edited.
        !            13:  *
        !            14:  * The editor does not garbage collect the temporary file.  When a new
        !            15:  * file is edited, the temporary file is rather discarded and a new one
        !            16:  * created for the new file.  Garbage collection would be rather complicated
        !            17:  * in ex because of the general undo, and in any case would require more
        !            18:  * work when throwing lines away because marks would have be carefully
        !            19:  * checked before reallocating temporary file space.  Said another way,
        !            20:  * each time you create a new line in the temporary file you get a unique
        !            21:  * number back, and this is a property used by marks.
        !            22:  *
        !            23:  * The following temp file parameters allow 256k bytes in the temporary
        !            24:  * file.  By changing to the numbers in comments you can get 512k.
        !            25:  * For VMUNIX you get more than you could ever want.
        !            26:  * VMUNIX uses long (32 bit) integers giving much more
        !            27:  * space in the temp file and no waste.  This doubles core
        !            28:  * requirements but allows files of essentially unlimited size to be edited.
        !            29:  */
        !            30: #ifndef VMUNIX
        !            31: #define        BLKMSK  0777            /* 01777 */
        !            32: #define        BNDRY   8               /* 16 */
        !            33: #define        INCRMT  0200            /* 0100 */
        !            34: #define        LBTMSK  0770            /* 0760 */
        !            35: #define        NMBLKS  506             /* 1018 */
        !            36: #define        OFFBTS  7               /* 6 */
        !            37: #define        OFFMSK  0177            /* 077 */
        !            38: #define        SHFT    2               /* 3 */
        !            39: #else
        !            40: #define        BLKMSK  077777
        !            41: #define        BNDRY   2
        !            42: #define        INCRMT  02000
        !            43: #define        LBTMSK  01776
        !            44: #define        NMBLKS  077770
        !            45: #define        OFFBTS  10
        !            46: #define        OFFMSK  01777
        !            47: #define        SHFT    0
        !            48: #endif
        !            49: 
        !            50: /*
        !            51:  * The editor uses three buffers into the temporary file (ed uses two
        !            52:  * and is very similar).  These are two read buffers and one write buffer.
        !            53:  * Basically, the editor deals with the file as a sequence of BUFSIZ character
        !            54:  * blocks.  Each block contains some number of lines (and lines
        !            55:  * can run across block boundaries.
        !            56:  *
        !            57:  * New lines are written into the last block in the temporary file
        !            58:  * which is in core as obuf.  When a line is needed which isn't in obuf,
        !            59:  * then it is brought into an input buffer.  As there are two, the choice
        !            60:  * is to take the buffer into which the last read (of the two) didn't go.
        !            61:  * Thus this is a 2 buffer LRU replacement strategy.  Measurement
        !            62:  * shows that this saves roughly 25% of the buffer reads over a one
        !            63:  * input buffer strategy.  Since the editor (on our VAX over 1 week)
        !            64:  * spends (spent) roughly 30% of its time in the system read routine,
        !            65:  * this can be a big help.
        !            66:  */
        !            67: var bool       hitin2;         /* Last read hit was ibuff2 not ibuff */
        !            68: var bool       ichang2;        /* Have actually changed ibuff2 */
        !            69: var bool       ichanged;       /* Have actually changed ibuff */
        !            70: var short      iblock;         /* Temp file block number of ibuff (or -1) */
        !            71: var short      iblock2;        /* Temp file block number of ibuff2 (or -1) */
        !            72: var short      ninbuf;         /* Number useful chars left in input buffer */
        !            73: var short      nleft;          /* Number usable chars left in output buffer */
        !            74: var short      oblock;         /* Temp file block number of obuff (or -1) */
        !            75: #ifndef VMUNIX
        !            76: var short      tline;          /* Current temp file ptr */
        !            77: #else
        !            78: var int        tline;
        !            79: #endif
        !            80: 
        !            81: var char       ibuff[BUFSIZ];
        !            82: var char       ibuff2[BUFSIZ];
        !            83: var char       obuff[BUFSIZ];
        !            84: 
        !            85: /*
        !            86:  * Structure of the descriptor block which resides
        !            87:  * in the first block of the temporary file and is
        !            88:  * the guiding light for crash recovery.
        !            89:  *
        !            90:  * As the Blocks field below implies, there are temporary file blocks
        !            91:  * devoted to (some) image of the incore array of pointers into the temp
        !            92:  * file.  Thus, to recover from a crash we use these indices to get the
        !            93:  * line pointers back, and then use the line pointers to get the text back.
        !            94:  * Except for possible lost lines due to sandbagged I/O, the entire
        !            95:  * file (at the time of the last editor "sync") can be recovered from
        !            96:  * the temp file.
        !            97:  */
        !            98: 
        !            99: /* This definition also appears in expreserve.c... beware */
        !           100: struct         header {
        !           101:        time_t  Time;                   /* Time temp file last updated */
        !           102:        int     Uid;
        !           103: #ifndef VMUNIX
        !           104:        short   Flines;                 /* Number of lines in file */
        !           105: #else
        !           106:        int     Flines;
        !           107: #endif
        !           108:        char    Savedfile[FNSIZE];      /* The current file name */
        !           109:        short   Blocks[LBLKS];          /* Blocks where line pointers stashed */
        !           110: }; 
        !           111: var struct     header H;
        !           112: 
        !           113: #define        uid             H.Uid
        !           114: #define        flines          H.Flines
        !           115: #define        savedfile       H.Savedfile
        !           116: #define        blocks          H.Blocks

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