sliding_window.c

   1 /*
   2  * Licensed under a two-clause BSD-style license.
   3  * See LICENSE for details.
   4  */
   5
   6 #include "git-compat-util.h"
   7 #include "sliding_window.h"
   8 #include "line_buffer.h"
   9 #include "strbuf.h"
  10
  11 static void strbuf_remove_from_left(struct strbuf *sb, size_t nbytes)
  12 {
  13         assert(nbytes <= sb->len);
  14         memmove(sb->buf, sb->buf + nbytes, sb->len - nbytes);
  15         strbuf_setlen(sb, sb->len - nbytes);
  16 }
  17
  18 static int check_overflow(off_t a, size_t b)
  19 {
  20         if ((off_t) b < 0)
  21                 return error("Unrepresentable length: "
  22                                 "%"PRIu64" > OFF_MAX", (uint64_t) b);
  23         if (signed_add_overflows(a, (off_t) b))
  24                 return error("Unrepresentable offset: "
  25                                 "%"PRIu64" + %"PRIu64" > OFF_MAX",
  26                                 (uint64_t) a, (uint64_t) b);
  27         return 0;
  28 }
  29
  30 int move_window(struct view *view, off_t off, size_t len)
  31 {
  32         off_t file_offset;
  33         assert(view && view->file);
  34         assert(!check_overflow(view->off, view->buf.len));
  35
  36         if (check_overflow(off, len))
  37                 return -1;
  38         if (off < view->off || off + len < view->off + view->buf.len)
  39                 return error("Invalid delta: window slides left");
  40
  41         file_offset = view->off + view->buf.len;
  42         if (off < file_offset)
  43                 /* Move the overlapping region into place. */
  44                 strbuf_remove_from_left(&view->buf, off - view->off);
  45         else
  46                 strbuf_setlen(&view->buf, 0);
  47         if (off > file_offset) {
  48                 /* Seek ahead to skip the gap. */
  49                 const off_t gap = off - file_offset;
  50                 const off_t nread = buffer_skip_bytes(view->file, gap);
  51                 if (nread != gap) {
  52                         if (!buffer_ferror(view->file))
  53                                 return error("Preimage ends early");
  54                         return error("Cannot seek forward in input: %s",
  55                                      strerror(errno));
  56                 }
  57                 file_offset += gap;
  58         }
  59         buffer_read_binary(&view->buf, len - view->buf.len, view->file);
  60         if (view->buf.len != len) {
  61                 if (!buffer_ferror(view->file))
  62                         return error("Preimage ends early");
  63                 return error("Cannot read preimage: %s", strerror(errno));
  64         }
  65         view->off = off;
  66         return 0;
  67 }