Andrew's git - gitweb.git/blob - vcs-svn/sliding

   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
  11static int input_error(struct line_buffer *file)
  12{
  13        if (!buffer_ferror(file))
  14                return error("delta preimage ends early");
  15        return error("cannot read delta preimage: %s", strerror(errno));
  16}
  17
  18static int skip_or_whine(struct line_buffer *file, off_t gap)
  19{
  20        if (buffer_skip_bytes(file, gap) != gap)
  21                return input_error(file);
  22        return 0;
  23}
  24
  25static int read_to_fill_or_whine(struct line_buffer *file,
  26                                struct strbuf *buf, size_t width)
  27{
  28        buffer_read_binary(file, buf, width - buf->len);
  29        if (buf->len != width)
  30                return input_error(file);
  31        return 0;
  32}
  33
  34static int check_overflow(off_t a, size_t b)
  35{
  36        if (b > maximum_signed_value_of_type(off_t))
  37                return error("unrepresentable length in delta: "
  38                                "%"PRIuMAX" > OFF_MAX", (uintmax_t) b);
  39        if (signed_add_overflows(a, (off_t) b))
  40                return error("unrepresentable offset in delta: "
  41                                "%"PRIuMAX" + %"PRIuMAX" > OFF_MAX",
  42                                (uintmax_t) a, (uintmax_t) b);
  43        return 0;
  44}
  45
  46int move_window(struct sliding_view *view, off_t off, size_t width)
  47{
  48        off_t file_offset;
  49        assert(view);
  50        assert(view->width <= view->buf.len);
  51        assert(!check_overflow(view->off, view->buf.len));
  52
  53        if (check_overflow(off, width))
  54                return -1;
  55        if (off < view->off || off + width < view->off + view->width)
  56                return error("invalid delta: window slides left");
  57        if (view->max_off >= 0 && view->max_off < off + width)
  58                return error("delta preimage ends early");
  59
  60        file_offset = view->off + view->buf.len;
  61        if (off < file_offset) {
  62                /* Move the overlapping region into place. */
  63                strbuf_remove(&view->buf, 0, off - view->off);
  64        } else {
  65                /* Seek ahead to skip the gap. */
  66                if (skip_or_whine(view->file, off - file_offset))
  67                        return -1;
  68                strbuf_setlen(&view->buf, 0);
  69        }
  70
  71        if (view->buf.len > width)
  72                ; /* Already read. */
  73        else if (read_to_fill_or_whine(view->file, &view->buf, width))
  74                return -1;
  75
  76        view->off = off;
  77        view->width = width;
  78        return 0;
  79}