tndbsubstitute.c - plan9port - [fork] Plan 9 from user space
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       ---
       tndbsubstitute.c (692B)
       ---
            1 #include <u.h>
            2 #include <libc.h>
            3 #include <bio.h>
            4 #include <ndb.h>
            5 
            6 /* replace a in t with b, the line structure in b is lost, c'est la vie */
            7 Ndbtuple*
            8 ndbsubstitute(Ndbtuple *t, Ndbtuple *a, Ndbtuple *b)
            9 {
           10         Ndbtuple *nt;
           11 
           12         if(a == b)
           13                 return t;
           14         if(b == nil)
           15                 return ndbdiscard(t, a);
           16 
           17         /* all pointers to a become pointers to b */
           18         for(nt = t; nt != nil; nt = nt->entry){
           19                 if(nt->line == a)
           20                         nt->line = b;
           21                 if(nt->entry == a)
           22                         nt->entry = b;
           23         }
           24 
           25         /* end of b chain points to a's successors */
           26         for(nt = b; nt->entry; nt = nt->entry){
           27                 nt->line = nt->entry;
           28         }
           29         nt->line = a->line;
           30         nt->entry = a->entry;
           31 
           32         a->entry = nil;
           33         ndbfree(a);
           34 
           35         if(a == t)
           36                 return b;
           37         else
           38                 return t;
           39 }