Bell 32V development

[unix-history] / usr / src / cmd / sdb / bio.c

#include "bio.h"

/*
* NAMES:  bread(), brseek(), blseek()
*
* DESCRIPTION:
*       This is a buffered read package.
*
*       Bread may be called with a negative nbytes which causes it to
*      read backwards.  In this case, buffer should point to the first
*      byte following the buffer.  If only a partial read is possible
*      (due to beginning of file), only the last bytes of the buffer
*      will be filled.
*/


bread(brs, buff, nbytes)
struct brbuf *brs; char *buff; {
       register int k, nb;

       if (nbytes > 0) {
               for (nb=nbytes; nb>0; nb--) {
                       if (brs->nr == 0) {
                               brs->nr = read(brs->fd, brs->next=brs->b, 512);
                               brs->nl = 0;
                               if (brs->nr < 0) return(-1);
                               if (brs->nr == 0) return(nbytes-nb);
                               }
                       *buff++ = *brs->next++;
                       brs->nr--;
                       brs->nl++;
                       }
               }
       else {
               nbytes = -nbytes;
               for (nb=nbytes; nb>0; nb--) {
                       if (brs->nl == 0) {
                               lseek(brs->fd, (long) -(512 + brs->nr), 1);
                               brs->nl = read(brs->fd, brs->b, 512);
                               if (brs->nl < 0) {
                                       for (k=511; k>0; k--) {
                                               lseek(brs->fd, 1, 1);
                                               brs->nl = read(brs->fd, brs->b, k);
                                               if (brs->nl >= 0) break;
                                               }
                                       if (brs->nl < 0) return(nbytes-nb);
                                       }
                               if (brs->nl == 0) return(nbytes-nb);
                               brs->next = brs->b + brs->nl;
                               brs->nr = 0;
                               }
                       *--buff = *--brs->next;
                       brs->nr++;
                       brs->nl--;
                       }
               }
       return(nbytes);
       }

blseek(brs, offset, flag) 
struct brbuf *brs; long offset; {
       brs->nl = 0;
       brs->nr = 0;
       return(lseek(brs->fd,offset,flag));
       }

binit(brs)
struct brbuf *brs; {
       brs->nl = brs->nr = 0;
}