Annotation of gforth/blocks.fs, revision 1.2

1.1       anton       1: \ A simple immplementation of the blocks wordset. 
                      2: 
                      3: \ This implementation uses only a single buffer and will therefore be a
                      4: \ little slow. An efficient implementation would use mmap on OSs that
                      5: \ provide it and many buffers on OSs that do not provide mmap.
                      6: 
                      7: \ I think I avoid the assumption 1 char = 1 here, but I have not tested this
                      8: 
1.2     ! pazsan      9: \ 1024 constant chars/block \ mandated by the standard
1.1       anton      10: 
                     11: create block-buffer chars/block chars allot
                     12: 
                     13: variable buffer-block 0 buffer-block ! \ the block currently in the buffer
                     14: variable block-fid 0 block-fid ! \ the file id of the current block file
                     15: variable buffer-dirty buffer-dirty off
                     16: 
                     17: 
                     18: : get-block-fid ( -- fid )
                     19:     block-fid @ 0=
                     20:     if
                     21:        s" blocks.fb" r/w open-file 0<>
                     22:        if
                     23:            s" blocks.fb" r/w create-file .s throw
                     24:        then
                     25:        block-fid !
                     26:     then
                     27:     block-fid @ ;
                     28: 
                     29: : block-position ( u -- )
                     30:     \ positions the block file to the start of block u
                     31:     1- chars/block chars um* get-block-fid reposition-file .s throw ;
                     32: 
                     33: : update ( -- )
                     34:     buffer-dirty on ;
                     35: 
                     36: : save-buffers ( -- )
                     37:     buffer-dirty @
                     38:     if
                     39:        buffer-block @ block-position
                     40:        block-buffer chars/block get-block-fid write-file throw
                     41:        buffer-dirty off
                     42:     endif ;
                     43: 
                     44: : empty-buffers ( -- )
                     45:     0 buffer-block ! ;
                     46: 
                     47: : flush ( -- )
                     48:     save-buffers
                     49:     empty-buffers ;
                     50: 
                     51: : block ( u -- a-addr )
                     52:     dup 0= -35 and throw
                     53:     dup buffer-block @ <>
                     54:     if
                     55:        save-buffers
                     56:        dup block-position
                     57:        block-buffer chars/block get-block-fid read-file .s throw
                     58:        \ clear the rest of the buffer if the file is too short
                     59:        block-buffer over chars + chars/block rot - blank
                     60:        buffer-block !    
                     61:     else
                     62:        drop
                     63:     then
                     64:     block-buffer ;
                     65: 
                     66: : buffer ( u -- a-addr )
                     67:     \ reading in the block is unnecessary, but simpler
                     68:     block ;
                     69: 
1.2     ! pazsan     70: User scr 0 scr !
1.1       anton      71: 
                     72: : list ( u -- )
                     73:     \ calling block again and again looks inefficient but is necessary
                     74:     \ in a multitasking environment
                     75:     dup scr !
                     76:     ." Screen " u. cr
                     77:     16 0
                     78:     ?do
                     79:        scr @ block i 64 * chars + 64 type cr
                     80:     loop ;
                     81: 
1.2     ! pazsan     82: : (source)  ( -- addr len )
        !            83:   blk @ ?dup
        !            84:   IF    block chars/block
        !            85:   ELSE  tib #tib @
        !            86:   THEN ;
        !            87: 
        !            88: ' (source) IS source
        !            89: 
        !            90: : load ( i*x n -- j*x )
        !            91:   push-file
        !            92:   dup loadline ! blk ! >in off ( ['] ) interpret ( catch )
        !            93:   pop-file ( throw ) ;
1.1       anton      94: 
1.2     ! pazsan     95: : thru ( i*x n1 n2 -- j*x )
        !            96:   1+ swap 0 ?DO  I load  LOOP ;
1.1       anton      97: 
1.2     ! pazsan     98: : +load ( i*x n -- j*x )  blk @ + load ;
        !            99: 
        !           100: : +thru ( i*x n1 n2 -- j*x )
        !           101:   1+ swap 0 ?DO  I +load  LOOP ;

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