ported fastbuf with effective backwards reading... incomplete

diff --git a/lib/fastbuf.h b/lib/fastbuf.h
index 68b2a9db18db938456fcefc309ccfb24a485ebcf..8535425335c04b1616fd024bedd34c49ecefd4df 100644 (file)
--- a/lib/fastbuf.h
+++ b/lib/fastbuf.h
@@ -166,9 +166,12 @@ fbatomic_commit(struct fastbuf *b)
 
 /* Configuring stream parameters */
 
-int bconfig(struct fastbuf *f, uns type, int data);
+enum bconfig_type {
+  BCONFIG_IS_TEMP_FILE,
+  BCONFIG_KEEP_BACK_BUF,
+};
 
-#define BCONFIG_IS_TEMP_FILE 0
+int bconfig(struct fastbuf *f, uns type, int data);
 
 /* Universal functions working on all fastbuf's */
 

diff --git a/lib/fb-file.c b/lib/fb-file.c
index 1f6dcb2eeab3632f709c04659cbc6dc6a8062af6..bf5684aff0aeaf284f3166c6c539b7f427de4e07 100644 (file)
--- a/lib/fb-file.c
+++ b/lib/fb-file.c
@@ -2,6 +2,7 @@
  *     UCW Library -- Fast Buffered I/O on Files
  *
  *     (c) 1997--2004 Martin Mares <mj@ucw.cz>
+ *     (c) 2007 Pavel Charvat <pchar@ucw.cz>
  *
  *     This software may be freely distributed and used according to the terms
  *     of the GNU Lesser General Public License.
@@ -20,6 +21,9 @@ struct fb_file {
   struct fastbuf fb;
   int fd;                              /* File descriptor */
   int is_temp_file;                    /* 0=normal file, 1=temporary file, delete on close, -1=shared FD */
+  int keep_back_buf;                   /* Optimize for backwards reading */
+  sh_off_t wpos;                       /* Real file position */
+  uns wlen;                            /* Window size */
 };
 #define FB_FILE(f) ((struct fb_file *)(f)->is_fastbuf)
 #define FB_BUFFER(f) (byte *)(FB_FILE(f) + 1)
@@ -27,22 +31,124 @@ struct fb_file {
 static int
 bfd_refill(struct fastbuf *f)
 {
-  f->bptr = f->buffer = FB_BUFFER(f);
-  int l = read(FB_FILE(f)->fd, f->buffer, f->bufend-f->buffer);
-  if (l < 0)
-    die("Error reading %s: %m", f->name);
-  f->bstop = f->buffer + l;
-  f->pos += l;
-  return l;
+  struct fb_file *F = FB_FILE(f);
+  byte *read_ptr = (f->buffer = FB_BUFFER(f));
+  uns blen = f->bufend - f->buffer, back = F->keep_back_buf ? blen >> 2 : 0, read_len = blen;
+  /* Forward or no seek */
+  if (F->wpos <= f->pos)
+    {
+      sh_off_t diff = f->pos - F->wpos;
+      if (diff > ((sh_off_t)blen << 2)) /* FIXME: Formula for long forward seeks */
+        {
+long_seek:
+         f->bptr = f->buffer + back;
+         f->bstop = f->buffer + blen;
+         goto seek;
+       }
+      if ((uns)diff < back) /* Reuse part of previous window (also F->wpos == f->pos) */
+        {
+         uns keep = back - (uns)diff;
+         if (keep >= F->wlen)
+           back = diff + (keep = F->wlen);
+         else
+           memmove(f->buffer, f->buffer + F->wlen - keep, keep);
+         read_len -= keep;
+         read_ptr += keep;
+       }
+      else /* Short forward seek */
+        {
+         uns skip = diff - back;
+         F->wpos += skip;
+         while (skip)
+           {
+             int l = read(F->fd, f->buffer, MIN(skip, blen));
+             if (unlikely(l <= 0))
+               if (l < 0)
+                 die("Error reading %s: %m", f->name);
+               else
+                 {
+                   F->wpos -= skip;
+                   goto eof;
+                 }
+             skip -= l;
+           }
+       }
+      f->bptr = f->buffer + back;
+      f->bstop = f->buffer + blen;
+    }
+  /* Backwards seek */
+  else
+    {
+      sh_off_t diff = F->wpos - f->pos;
+      if (diff > ((sh_off_t)blen << 1)) /* FIXME: Formula for long backwards seeks */
+        {
+         if ((sh_off_t)back > f->pos)
+           back = f->pos;
+         goto long_seek;
+       }
+      if ((uns)diff <= F->wlen) /* Seek into previous window (for example brewind) */
+        {
+         f->bstop = f->buffer + F->wlen;
+         f->bptr = f->bstop - diff;
+         f->pos = F->wpos;
+         return 1;
+       }
+      back *= 3;
+      if ((sh_off_t)back > f->pos)
+       back = f->pos;
+      f->bptr = f->buffer + back;
+      read_len = back + diff - F->wlen;
+      if (F->wlen && read_len < blen) /* Reuse part of previous window */
+        {
+         uns keep = MIN(F->wlen, blen - read_len);
+         memmove(f->buffer + read_len, f->buffer, keep);
+         f->bstop = f->buffer + read_len + keep;
+       }
+      else
+       f->bstop = f->buffer + (read_len = blen);
+seek:
+      F->wpos = f->pos + (f->buffer - f->bptr);
+      if (sh_seek(F->fd, F->wpos, SEEK_SET) < 0)
+       die("Error seeking %s: %m", f->name);
+    }
+  do
+    {
+      int l = read(F->fd, read_ptr, read_len);
+      if (unlikely(l < 0))
+       die("Error reading %s: %m", f->name);
+      if (!l)
+       if (unlikely(read_ptr < f->bptr))
+         goto eof;
+       else
+         break; /* Incomplete read because of EOF */
+      read_ptr += l;
+      read_len -= l;
+      F->wpos += l;
+    }
+  while (read_ptr <= f->bptr);
+  if (read_len)
+    f->bstop = read_ptr;
+  f->pos += f->bstop - f->bptr;
+  F->wlen = f->bstop - f->buffer;
+  return f->bstop - f->bptr;
+eof:
+  /* Seeked behind EOF */
+  f->bptr = f->bstop = f->buffer;
+  F->wlen = 0;
+  return 0;
 }
 
 static void
 bfd_spout(struct fastbuf *f)
 {
+  if (FB_FILE(f)->wpos != f->pos && sh_seek(FB_FILE(f)->fd, f->pos, SEEK_SET) < 0)
+    die("Error seeking %s: %m", f->name);
+
   int l = f->bptr - f->buffer;
   byte *c = f->buffer;
 
-  f->pos += l;
+  FB_FILE(f)->wpos = (f->pos += l);
+  FB_FILE(f)->wlen = 0;
   while (l)
     {
       int z = write(FB_FILE(f)->fd, c, l);
@@ -57,11 +163,28 @@ bfd_spout(struct fastbuf *f)
 static int
 bfd_seek(struct fastbuf *f, sh_off_t pos, int whence)
 {
-  sh_off_t l = sh_seek(FB_FILE(f)->fd, pos, whence);
-  if (l < 0)
-    return 0;
-  f->pos = l;
-  return 1;
+  sh_off_t l;
+  switch (whence)
+    {
+      case SEEK_SET:
+       f->pos = pos;
+       return 1;
+      case SEEK_CUR:
+       l = f->pos + pos;
+       if ((pos > 0) ^ (l > f->pos))
+         return 0;
+       f->pos = l;
+       return 1;
+      case SEEK_END:
+       l = sh_seek(FB_FILE(f)->fd, pos, SEEK_END);
+       if (l < 0)
+         return 0;
+       FB_FILE(f)->wpos = f->pos = l;
+       FB_FILE(f)->wlen = 0;
+       return 1;
+      default:
+       ASSERT(0);
+    }
 }
 
 static void
@@ -83,11 +206,14 @@ bfd_config(struct fastbuf *f, uns item, int value)
 {
   switch (item)
     {
-    case BCONFIG_IS_TEMP_FILE:
-      FB_FILE(f)->is_temp_file = value;
-      return 0;
-    default:
-      return -1;
+      case BCONFIG_IS_TEMP_FILE:
+       FB_FILE(f)->is_temp_file = value;
+       return 0;
+      case BCONFIG_KEEP_BACK_BUF:
+       FB_FILE(f)->keep_back_buf = value;
+       return 0;
+      default:
+       return -1;
     }
 }
 
@@ -96,7 +222,7 @@ bfdopen_internal(int fd, byte *name, uns buflen)
 {
   ASSERT(buflen);
   int namelen = strlen(name) + 1;
-  struct fb_file *F = xmalloc(sizeof(struct fb_file) + buflen + namelen);
+  struct fb_file *F = xmalloc_zero(sizeof(struct fb_file) + buflen + namelen);
   struct fastbuf *f = &F->fb;
 
   bzero(F, sizeof(*F));