sys/src/libbio/bseek.c

   1 #include        <u.h>
   2 #include        <libc.h>
   3 #include        <bio.h>
   4
   5 vlong
   6 Bseek(Biobufhdr *bp, vlong offset, int base)
   7 {
   8         vlong n, d;
   9
  10         switch(bp->state) {
  11         default:
  12                 fprint(2, "Bseek: unknown state %d\n", bp->state);
  13                 return Beof;
  14
  15         case Bracteof:
  16                 bp->state = Bractive;
  17                 bp->icount = 0;
  18                 bp->gbuf = bp->ebuf;
  19
  20         case Bractive:
  21                 n = offset;
  22                 if(base == 1) {
  23                         n += Boffset(bp);
  24                         base = 0;
  25                 }
  26
  27                 /*
  28                  * try to seek within buffer
  29                  */
  30                 if(base == 0) {
  31                         /*
  32                          * if d is too large for an int, icount may wrap,
  33                          * so we need to ensure that icount hasn't wrapped
  34                          * and points within the buffer's valid data.
  35                          */
  36                         d = n - Boffset(bp);
  37                         bp->icount += d;
  38                         if(d <= bp->bsize && bp->icount <= 0 &&
  39                             bp->ebuf - bp->gbuf >= -bp->icount)
  40                                 return n;
  41                 }
  42
  43                 /*
  44                  * reset the buffer
  45                  */
  46                 n = seek(bp->fid, n, base);
  47                 bp->icount = 0;
  48                 bp->gbuf = bp->ebuf;
  49                 break;
  50
  51         case Bwactive:
  52                 Bflush(bp);
  53                 n = seek(bp->fid, offset, base);
  54                 break;
  55         }
  56         bp->offset = n;
  57         return n;
  58 }