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Annotation of gforth/blocks.fs, revision 1.3

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: 
1.3     ! anton      18: \ the file is opened as binary file, since it either will contain text
        !            19: \ without newlines or binary data
1.1       anton      20: : get-block-fid ( -- fid )
                     21:     block-fid @ 0=
                     22:     if
1.3     ! anton      23:        s" blocks.fb" r/w bin open-file 0<>
1.1       anton      24:        if
1.3     ! anton      25:            s" blocks.fb" r/w bin create-file throw
1.1       anton      26:        then
                     27:        block-fid !
                     28:     then
                     29:     block-fid @ ;
                     30: 
                     31: : block-position ( u -- )
                     32:     \ positions the block file to the start of block u
1.3     ! anton      33:     1- chars/block chars um* get-block-fid reposition-file throw ;
1.1       anton      34: 
                     35: : update ( -- )
                     36:     buffer-dirty on ;
                     37: 
                     38: : save-buffers ( -- )
                     39:     buffer-dirty @
                     40:     if
                     41:        buffer-block @ block-position
                     42:        block-buffer chars/block get-block-fid write-file throw
                     43:        buffer-dirty off
                     44:     endif ;
                     45: 
                     46: : empty-buffers ( -- )
                     47:     0 buffer-block ! ;
                     48: 
                     49: : flush ( -- )
                     50:     save-buffers
                     51:     empty-buffers ;
                     52: 
                     53: : block ( u -- a-addr )
                     54:     dup 0= -35 and throw
                     55:     dup buffer-block @ <>
                     56:     if
                     57:        save-buffers
                     58:        dup block-position
1.3     ! anton      59:        block-buffer chars/block get-block-fid read-file throw
1.1       anton      60:        \ clear the rest of the buffer if the file is too short
                     61:        block-buffer over chars + chars/block rot - blank
                     62:        buffer-block !    
                     63:     else
                     64:        drop
                     65:     then
                     66:     block-buffer ;
                     67: 
                     68: : buffer ( u -- a-addr )
                     69:     \ reading in the block is unnecessary, but simpler
                     70:     block ;
                     71: 
1.2       pazsan     72: User scr 0 scr !
1.1       anton      73: 
                     74: : list ( u -- )
                     75:     \ calling block again and again looks inefficient but is necessary
                     76:     \ in a multitasking environment
                     77:     dup scr !
                     78:     ." Screen " u. cr
                     79:     16 0
                     80:     ?do
                     81:        scr @ block i 64 * chars + 64 type cr
                     82:     loop ;
                     83: 
1.2       pazsan     84: : (source)  ( -- addr len )
                     85:   blk @ ?dup
                     86:   IF    block chars/block
                     87:   ELSE  tib #tib @
                     88:   THEN ;
                     89: 
                     90: ' (source) IS source
                     91: 
                     92: : load ( i*x n -- j*x )
                     93:   push-file
                     94:   dup loadline ! blk ! >in off ( ['] ) interpret ( catch )
                     95:   pop-file ( throw ) ;
1.1       anton      96: 
1.2       pazsan     97: : thru ( i*x n1 n2 -- j*x )
                     98:   1+ swap 0 ?DO  I load  LOOP ;
1.1       anton      99: 
1.2       pazsan    100: : +load ( i*x n -- j*x )  blk @ + load ;
                    101: 
                    102: : +thru ( i*x n1 n2 -- j*x )
                    103:   1+ swap 0 ?DO  I +load  LOOP ;