sys/src/liboventi/zero.c

   1 #include <u.h>
   2 #include <libc.h>
   3 #include <oventi.h>
   4
   5 /* score of a zero length block */
   6 uchar   vtZeroScore[VtScoreSize] = {
   7         0xda, 0x39, 0xa3, 0xee, 0x5e, 0x6b, 0x4b, 0x0d, 0x32, 0x55,
   8         0xbf, 0xef, 0x95, 0x60, 0x18, 0x90, 0xaf, 0xd8, 0x07, 0x09
   9 };
  10
  11
  12 int
  13 vtZeroExtend(int type, uchar *buf, int n, int nn)
  14 {
  15         uchar *p, *ep;
  16
  17         switch(type) {
  18         default:
  19                 memset(buf+n, 0, nn-n);
  20                 break;
  21         case VtPointerType0:
  22         case VtPointerType1:
  23         case VtPointerType2:
  24         case VtPointerType3:
  25         case VtPointerType4:
  26         case VtPointerType5:
  27         case VtPointerType6:
  28         case VtPointerType7:
  29         case VtPointerType8:
  30         case VtPointerType9:
  31                 p = buf + (n/VtScoreSize)*VtScoreSize;
  32                 ep = buf + (nn/VtScoreSize)*VtScoreSize;
  33                 while(p < ep) {
  34                         memmove(p, vtZeroScore, VtScoreSize);
  35                         p += VtScoreSize;
  36                 }
  37                 memset(p, 0, buf+nn-p);
  38                 break;
  39         }
  40         return 1;
  41 }
  42
  43 int
  44 vtZeroTruncate(int type, uchar *buf, int n)
  45 {
  46         uchar *p;
  47
  48         switch(type) {
  49         default:
  50                 for(p = buf + n; p > buf; p--) {
  51                         if(p[-1] != 0)
  52                                 break;
  53                 }
  54                 return p - buf;
  55         case VtRootType:
  56                 if(n < VtRootSize)
  57                         return n;
  58                 return VtRootSize;
  59         case VtPointerType0:
  60         case VtPointerType1:
  61         case VtPointerType2:
  62         case VtPointerType3:
  63         case VtPointerType4:
  64         case VtPointerType5:
  65         case VtPointerType6:
  66         case VtPointerType7:
  67         case VtPointerType8:
  68         case VtPointerType9:
  69                 /* ignore slop at end of block */
  70                 p = buf + (n/VtScoreSize)*VtScoreSize;
  71
  72                 while(p > buf) {
  73                         if(memcmp(p - VtScoreSize, vtZeroScore, VtScoreSize) != 0)
  74                                 break;
  75                         p -= VtScoreSize;
  76                 }
  77                 return p - buf;
  78         }
  79 }