X-Git-Url: https://code.delx.au/gnu-emacs-elpa/blobdiff_plain/a43c92f5481895d492c4323f880ac89cb13d69f6..bdea86718db09678b8f16b2756ef458c544daaef:/packages/vlf/vlf.el

diff --git a/packages/vlf/vlf.el b/packages/vlf/vlf.el
index 4e85d14de..8eb2a4ca3 100644
--- a/packages/vlf/vlf.el
+++ b/packages/vlf/vlf.el
@@ -1,13 +1,14 @@
 ;;; vlf.el --- View Large Files  -*- lexical-binding: t -*-
 
-;; Copyright (C) 2006, 2012, 2013  Free Software Foundation, Inc.
+;; Copyright (C) 2006, 2012-2014 Free Software Foundation, Inc.
 
-;; Version: 0.9
+;; Version: 1.5
 ;; Keywords: large files, utilities
 ;; Maintainer: Andrey Kotlarski <m00naticus@gmail.com>
 ;; Authors: 2006 Mathias Dahl <mathias.dahl@gmail.com>
 ;;          2012 Sam Steingold <sds@gnu.org>
-;;          2013 Andrey Kotlarski <m00naticus@gmail.com>
+;;          2013-2014 Andrey Kotlarski <m00naticus@gmail.com>
+;; URL: https://github.com/m00natic/vlfi
 
 ;; This file is free software; you can redistribute it and/or modify
 ;; it under the terms of the GNU General Public License as published by
@@ -25,11 +26,12 @@
 ;; Boston, MA 02111-1307, USA.
 
 ;;; Commentary:
-
-;; This package provides the M-x vlf command, which visits part of a
-;; large file without loading the entire file.
-;; The buffer uses VLF mode, which defines several commands for
-;; moving around, searching and editing selected part of file.
+;; This package provides the M-x vlf command, which visits part of
+;; large file without loading it entirely.  The buffer uses VLF mode,
+;; which provides several commands for moving around, searching,
+;; comparing and editing selected part of file.
+;; To have it offered when opening large files:
+;; (require 'vlf-integrate)
 
 ;; This package was inspired by a snippet posted by Kevin Rodgers,
 ;; showing how to use `insert-file-contents' to extract part of a
@@ -37,26 +39,42 @@
 
 ;;; Code:
 
-(defgroup vlf nil
-  "View Large Files in Emacs."
-  :prefix "vlf-"
-  :group 'files)
-
-(defcustom vlf-batch-size 1024
-  "Defines how large each batch of file data is (in bytes)."
-  :type 'integer
-  :group 'vlf)
-
-;;; Keep track of file position.
-(defvar vlf-start-pos 0
-  "Absolute position of the visible chunk start.")
-(defvar vlf-end-pos 0 "Absolute position of the visible chunk end.")
-(defvar vlf-file-size 0 "Total size of presented file.")
+(defgroup vlf nil "View Large Files in Emacs."
+  :prefix "vlf-" :group 'files)
+
+(defcustom vlf-before-batch-functions nil
+  "Hook that runs before multiple batch operations.
+One argument is supplied that specifies current action.  Possible
+values are: `write', `ediff', `occur', `search', `goto-line'."
+  :group 'vlf :type 'hook)
+
+(defcustom vlf-after-batch-functions nil
+  "Hook that runs after multiple batch operations.
+One argument is supplied that specifies current action.  Possible
+values are: `write', `ediff', `occur', `search', `goto-line'."
+  :group 'vlf :type 'hook)
+
+(require 'vlf-base)
+
+(autoload 'vlf-write "vlf-write" "Write current chunk to file." t)
+(autoload 'vlf-re-search-forward "vlf-search"
+  "Search forward for REGEXP prefix COUNT number of times." t)
+(autoload 'vlf-re-search-backward "vlf-search"
+  "Search backward for REGEXP prefix COUNT number of times." t)
+(autoload 'vlf-goto-line "vlf-search" "Go to line." t)
+(autoload 'vlf-occur "vlf-occur"
+  "Make whole file occur style index for REGEXP." t)
+(autoload 'vlf-toggle-follow "vlf-follow"
+  "Toggle continuous chunk recenter around current point." t)
+(autoload 'vlf-stop-follow "vlf-follow" "Stop continuous recenter." t)
+(autoload 'vlf-ediff-buffers "vlf-ediff"
+  "Run batch by batch ediff over VLF buffers." t)
 
 (defvar vlf-mode-map
   (let ((map (make-sparse-keymap)))
-    (define-key map [M-next] 'vlf-next-batch)
-    (define-key map [M-prior] 'vlf-prev-batch)
+    (define-key map "n" 'vlf-next-batch)
+    (define-key map "p" 'vlf-prev-batch)
+    (define-key map " " 'vlf-next-batch-from-point)
     (define-key map "+" 'vlf-change-batch-size)
     (define-key map "-"
       (lambda () "Decrease vlf batch size by factor of 2."
@@ -67,113 +85,160 @@
     (define-key map "o" 'vlf-occur)
     (define-key map "[" 'vlf-beginning-of-file)
     (define-key map "]" 'vlf-end-of-file)
-    (define-key map "e" 'vlf-edit-mode)
     (define-key map "j" 'vlf-jump-to-chunk)
     (define-key map "l" 'vlf-goto-line)
+    (define-key map "e" 'vlf-ediff-buffers)
+    (define-key map "f" 'vlf-toggle-follow)
+    (define-key map "g" 'vlf-revert)
     map)
   "Keymap for `vlf-mode'.")
 
-(define-derived-mode vlf-mode special-mode "VLF"
-  "Mode to browse large files in."
-  (setq buffer-read-only t)
-  (set-buffer-modified-p nil)
-  (buffer-disable-undo)
-  (make-local-variable 'write-file-functions)
-  (add-hook 'write-file-functions 'vlf-write)
-  (make-local-variable 'revert-buffer-function)
-  (setq revert-buffer-function 'vlf-revert)
-  (make-local-variable 'vlf-batch-size)
-  (put 'vlf-batch-size 'permanent-local t)
-  (make-local-variable 'vlf-start-pos)
-  (put 'vlf-start-pos 'permanent-local t)
-  (make-local-variable 'vlf-end-pos)
-  (put 'vlf-end-pos 'permanent-local t)
-  (make-local-variable 'vlf-file-size)
-  (put 'vlf-file-size 'permanent-local t))
-
-;;;###autoload
-(defun vlf (file)
-  "View Large FILE.
-Batches of the file data from FILE will be displayed in a read-only
-buffer.  You can customize number of bytes displayed by customizing
-`vlf-batch-size'."
-  (interactive "fFile to open: ")
-  (with-current-buffer (generate-new-buffer "*vlf*")
-    (vlf-mode)
-    (setq buffer-file-name file
-          vlf-file-size (vlf-get-file-size file))
-    (vlf-insert-file)
-    (switch-to-buffer (current-buffer))))
+(defvar vlf-prefix-map
+  (let ((map (make-sparse-keymap)))
+    (define-key map "\C-c\C-v" vlf-mode-map)
+    map)
+  "Prefixed keymap for `vlf-mode'.")
 
-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-;;; integration with other packages
+(define-minor-mode vlf-mode
+  "Mode to browse large files in."
+  :lighter " VLF" :group 'vlf :keymap vlf-prefix-map
+  (cond (vlf-mode
+         (set (make-local-variable 'require-final-newline) nil)
+         (add-hook 'write-file-functions 'vlf-write nil t)
+         (set (make-local-variable 'revert-buffer-function)
+              'vlf-revert)
+         (make-local-variable 'vlf-batch-size)
+         (setq vlf-file-size (vlf-get-file-size buffer-file-truename)
+               vlf-start-pos 0
+               vlf-end-pos 0)
+         (let* ((pos (position-bytes (point)))
+                (start (* (/ pos vlf-batch-size) vlf-batch-size)))
+           (goto-char (byte-to-position (- pos start)))
+           (vlf-move-to-batch start))
+         (add-hook 'after-change-major-mode-hook 'vlf-keep-alive t t)
+         (vlf-keep-alive))
+        ((or (not large-file-warning-threshold)
+             (< vlf-file-size large-file-warning-threshold)
+             (y-or-n-p (format "Load whole file (%s)? "
+                               (file-size-human-readable
+                                vlf-file-size))))
+         (kill-local-variable 'revert-buffer-function)
+         (vlf-stop-follow)
+         (kill-local-variable 'require-final-newline)
+         (remove-hook 'write-file-functions 'vlf-write t)
+         (remove-hook 'after-change-major-mode-hook
+                      'vlf-keep-alive t)
+         (let ((hexl (derived-mode-p 'hexl-mode)))
+           (if hexl (hexl-mode-exit))
+           (let ((pos (+ vlf-start-pos (position-bytes (point)))))
+             (vlf-with-undo-disabled
+              (insert-file-contents buffer-file-name t nil nil t))
+             (goto-char (byte-to-position pos)))
+           (if hexl (hexl-mode)))
+         (rename-buffer (file-name-nondirectory buffer-file-name) t))
+        (t (setq vlf-mode t))))
+
+(defun vlf-keep-alive ()
+  "Keep `vlf-mode' on major mode change."
+  (if (derived-mode-p 'hexl-mode)
+      (set (make-local-variable 'revert-buffer-function) 'vlf-revert))
+  (setq vlf-mode t))
 
 ;;;###autoload
-(defun dired-vlf ()
-  "In Dired, visit the file on this line in VLF mode."
-  (interactive)
-  (vlf (dired-get-file-for-visit)))
+(defun vlf (file &optional minimal)
+  "View Large FILE in batches.  When MINIMAL load just a few bytes.
+You can customize number of bytes displayed by customizing
+`vlf-batch-size'.
+Return newly created buffer."
+  (interactive (list (read-file-name "File to open: ") nil))
+  (let ((vlf-buffer (generate-new-buffer "*vlf*")))
+    (set-buffer vlf-buffer)
+    (set-visited-file-name file)
+    (set-buffer-modified-p nil)
+    (if (or minimal (file-remote-p file))
+        (set (make-local-variable 'vlf-batch-size) 1024))
+    (vlf-mode 1)
+    (when minimal                 ;restore batch size to default value
+      (kill-local-variable 'vlf-batch-size)
+      (make-local-variable 'vlf-batch-size))
+    (switch-to-buffer vlf-buffer)
+    vlf-buffer))
 
-;;;###autoload
-(eval-after-load "dired"
-  '(define-key dired-mode-map "V" 'dired-vlf))
+(defun vlf-next-batch (append)
+  "Display the next batch of file data.
+When prefix argument is supplied and positive
+ jump over APPEND number of batches.
+When prefix argument is negative
+ append next APPEND number of batches to the existing buffer."
+  (interactive "p")
+  (vlf-verify-size)
+  (let* ((end (min (+ vlf-end-pos (* vlf-batch-size (abs append)))
+                   vlf-file-size))
+         (start (if (< append 0)
+                    vlf-start-pos
+                  (- end vlf-batch-size))))
+    (vlf-move-to-chunk start end)))
 
-;;;###autoload
-(defun vlf-if-file-too-large (size op-type &optional filename)
-  "If file SIZE larger than `large-file-warning-threshold', \
-allow user to view file with `vlf', open it normally, or abort.
-OP-TYPE specifies the file operation being performed over FILENAME."
-  (and large-file-warning-threshold size
-       (> size large-file-warning-threshold)
-       (let ((char nil))
-         (while (not (memq (setq char
-                                 (read-event
-                                  (propertize
-                                   (format
-                                    "File %s is large (%s): \
-%s normally (o), %s with vlf (v) or abort (a)"
-                                    (if filename
-                                        (file-name-nondirectory filename)
-                                      "")
-                                    (file-size-human-readable size)
-                                    op-type op-type)
-                                   'face 'minibuffer-prompt)))
-                           '(?o ?O ?v ?V ?a ?A))))
-         (cond ((memq char '(?o ?O)))
-               ((memq char '(?v ?V))
-                (vlf filename)
-                (error ""))
-               ((memq char '(?a ?A))
-                (error "Aborted"))))))
-
-;; hijack `abort-if-file-too-large'
-;;;###autoload
-(fset 'abort-if-file-too-large 'vlf-if-file-too-large)
+(defun vlf-prev-batch (prepend)
+  "Display the previous batch of file data.
+When prefix argument is supplied and positive
+ jump over PREPEND number of batches.
+When prefix argument is negative
+ append previous PREPEND number of batches to the existing buffer."
+  (interactive "p")
+  (if (zerop vlf-start-pos)
+      (error "Already at BOF"))
+  (let* ((start (max 0 (- vlf-start-pos (* vlf-batch-size (abs prepend)))))
+         (end (if (< prepend 0)
+                  vlf-end-pos
+                (+ start vlf-batch-size))))
+    (vlf-move-to-chunk start end)))
 
 ;; scroll auto batching
 (defadvice scroll-up (around vlf-scroll-up
                              activate compile)
   "Slide to next batch if at end of buffer in `vlf-mode'."
-  (if (and (eq major-mode 'vlf-mode)
-           (eobp))
+  (if (and vlf-mode (pos-visible-in-window-p (point-max)))
       (progn (vlf-next-batch 1)
              (goto-char (point-min)))
     ad-do-it))
 
 (defadvice scroll-down (around vlf-scroll-down
                                activate compile)
-  "Slide to previous batch if at beginning of buffer  in `vlf-mode'."
-  (if (and (eq major-mode 'vlf-mode)
-           (bobp))
+  "Slide to previous batch if at beginning of buffer in `vlf-mode'."
+  (if (and vlf-mode (pos-visible-in-window-p (point-min)))
       (progn (vlf-prev-batch 1)
              (goto-char (point-max)))
     ad-do-it))
 
-;; non-recent Emacs
-(unless (fboundp 'file-size-human-readable)
-  (defun file-size-human-readable (file-size)
-    "Print FILE-SIZE in MB."
-    (format "%.1fMB" (/ file-size 1048576.0))))
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;; hexl mode integration
+
+(eval-after-load "hexl"
+  '(progn
+     (defadvice hexl-save-buffer (around vlf-hexl-save
+                                         activate compile)
+       "Prevent hexl save if `vlf-mode' is active."
+       (if vlf-mode
+           (vlf-write)
+         ad-do-it))
+
+     (defadvice hexl-scroll-up (around vlf-hexl-scroll-up
+                                       activate compile)
+       "Slide to next batch if at end of buffer in `vlf-mode'."
+       (if (and vlf-mode (pos-visible-in-window-p (point-max))
+                (or (not (numberp arg)) (< 0 arg)))
+           (progn (vlf-next-batch 1)
+                  (goto-char (point-min)))
+         ad-do-it))
+
+     (defadvice hexl-scroll-down (around vlf-hexl-scroll-down
+                                         activate compile)
+       "Slide to previous batch if at beginning of buffer in `vlf-mode'."
+       (if (and vlf-mode (pos-visible-in-window-p (point-min)))
+           (progn (vlf-prev-batch 1)
+                  (goto-char (point-max)))
+         ad-do-it))))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;; utilities
@@ -183,680 +248,64 @@ OP-TYPE specifies the file operation being performed over FILENAME."
 Normally, the value is doubled;
 with the prefix argument DECREASE it is halved."
   (interactive "P")
-  (or (assq 'vlf-batch-size (buffer-local-variables))
-      (error "%s is not local in this buffer" 'vlf-batch-size))
-  (setq vlf-batch-size (if decrease
-                            (/ vlf-batch-size 2)
-                          (* vlf-batch-size 2)))
-  (vlf-move-to-batch vlf-start-pos))
+  (vlf-set-batch-size (if decrease (/ vlf-batch-size 2)
+                        (* vlf-batch-size 2))))
 
-(defun vlf-format-buffer-name ()
-  "Return format for vlf buffer name."
-  (format "%s(%s)[%d/%d](%d)"
-          (file-name-nondirectory buffer-file-name)
-          (file-size-human-readable vlf-file-size)
-          (/ vlf-end-pos vlf-batch-size)
-          (/ vlf-file-size vlf-batch-size)
-          vlf-batch-size))
-
-(defun vlf-update-buffer-name ()
-  "Update the current buffer name."
-  (rename-buffer (vlf-format-buffer-name) t))
-
-(defun vlf-get-file-size (file)
-  "Get size in bytes of FILE."
-  (nth 7 (file-attributes file)))
-
-(defun vlf-insert-file (&optional from-end)
-  "Insert first chunk of current file contents in current buffer.
-With FROM-END prefix, start from the back."
-  (if from-end
-      (setq vlf-start-pos (max 0 (- vlf-file-size vlf-batch-size))
-            vlf-end-pos vlf-file-size)
-    (setq vlf-start-pos 0
-          vlf-end-pos (min vlf-batch-size vlf-file-size)))
-  (vlf-move-to-chunk vlf-start-pos vlf-end-pos))
+(defun vlf-set-batch-size (size)
+  "Set batch to SIZE bytes and update chunk."
+  (interactive (list (read-number "Size in bytes: " vlf-batch-size)))
+  (setq vlf-batch-size size)
+  (vlf-move-to-batch vlf-start-pos))
 
 (defun vlf-beginning-of-file ()
   "Jump to beginning of file content."
   (interactive)
-  (vlf-insert-file))
+  (vlf-move-to-batch 0))
 
 (defun vlf-end-of-file ()
   "Jump to end of file content."
   (interactive)
-  (vlf-insert-file t))
+  (vlf-verify-size)
+  (vlf-move-to-batch vlf-file-size))
 
-(defun vlf-revert (&optional _ignore-auto noconfirm)
-  "Revert current chunk.  Ignore IGNORE-AUTO.
+(defun vlf-revert (&optional _auto noconfirm)
+  "Revert current chunk.  Ignore _AUTO.
 Ask for confirmation if NOCONFIRM is nil."
-  (or noconfirm
-      (yes-or-no-p (format "Revert buffer from file %s? "
-                           buffer-file-name))
-      (vlf-move-to-chunk vlf-start-pos vlf-end-pos)))
+  (interactive)
+  (when (or noconfirm
+            (yes-or-no-p (format "Revert buffer from file %s? "
+                                 buffer-file-name)))
+    (set-buffer-modified-p nil)
+    (vlf-move-to-chunk-2 vlf-start-pos vlf-end-pos)))
 
 (defun vlf-jump-to-chunk (n)
   "Go to to chunk N."
   (interactive "nGoto to chunk: ")
   (vlf-move-to-batch (* (1- n) vlf-batch-size)))
 
-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-;;; batch movement
-
-(defun vlf-next-batch (append)
-  "Display the next batch of file data.
-When prefix argument is supplied and positive
- jump over APPEND number of batches.
-When prefix argument is negative
- append next APPEND number of batches to the existing buffer."
-  (interactive "p")
-  (or (verify-visited-file-modtime (current-buffer))
-      (setq vlf-file-size (vlf-get-file-size buffer-file-name)))
-  (let ((end (min (+ vlf-end-pos (* vlf-batch-size
-                                     (abs append)))
-                  vlf-file-size)))
-    (let ((inhibit-read-only t)
-          (do-append (< append 0))
-          (pos (position-bytes (point))))
-      (if do-append
-          (goto-char (point-max))
-        (setq vlf-start-pos (- end vlf-batch-size))
-        (erase-buffer))
-      (insert-file-contents buffer-file-name nil (if do-append
-                                                     vlf-end-pos
-                                                   vlf-start-pos)
-                            end)
-      (setq vlf-end-pos end)
-      (goto-char (or (byte-to-position (+ pos (vlf-adjust-chunk)))
-                     (point-max)))))
-  (set-visited-file-modtime)
-  (set-buffer-modified-p nil)
-  (vlf-update-buffer-name))
-
-(defun vlf-prev-batch (prepend)
-  "Display the previous batch of file data.
-When prefix argument is supplied and positive
- jump over PREPEND number of batches.
-When prefix argument is negative
- append previous PREPEND number of batches to the existing buffer."
-  (interactive "p")
-  (if (zerop vlf-start-pos)
-      (error "Already at BOF"))
-  (or (verify-visited-file-modtime (current-buffer))
-      (setq vlf-file-size (vlf-get-file-size buffer-file-name)))
-  (let ((inhibit-read-only t)
-        (start (max 0 (- vlf-start-pos (* vlf-batch-size
-                                           (abs prepend)))))
-        (do-prepend (< prepend 0))
-        (pos (- (position-bytes (point-max))
-                (position-bytes (point)))))
-    (if do-prepend
-        (goto-char (point-min))
-      (setq vlf-end-pos (min (+ start vlf-batch-size)
-                              vlf-file-size))
-      (erase-buffer))
-    (insert-file-contents buffer-file-name nil start
-                          (if do-prepend
-                              vlf-start-pos
-                            vlf-end-pos))
-    (setq vlf-start-pos start)
-    (setq pos (+ pos (vlf-adjust-chunk)))
-    (goto-char (or (byte-to-position (- (position-bytes (point-max))
-                                        pos))
-                   (point-max))))
-  (set-visited-file-modtime)
-  (set-buffer-modified-p nil)
-  (vlf-update-buffer-name))
+(defun vlf-no-modifications ()
+  "Ensure there are no buffer modifications."
+  (if (buffer-modified-p)
+      (error "Save or discard your changes first")
+    t))
 
 (defun vlf-move-to-batch (start &optional minimal)
   "Move to batch determined by START.
 Adjust according to file start/end and show `vlf-batch-size' bytes.
 When given MINIMAL flag, skip non important operations."
-  (or (verify-visited-file-modtime (current-buffer))
-      (setq vlf-file-size (vlf-get-file-size buffer-file-name)))
-  (setq vlf-start-pos (max 0 start)
-        vlf-end-pos (min (+ vlf-start-pos vlf-batch-size)
-                          vlf-file-size))
-  (if (= vlf-file-size vlf-end-pos)   ; re-check file size
-      (setq vlf-start-pos (max 0 (- vlf-end-pos vlf-batch-size))))
-  (let ((inhibit-read-only t)
-        (pos (position-bytes (point))))
-    (erase-buffer)
-    (insert-file-contents buffer-file-name nil
-                          vlf-start-pos vlf-end-pos)
-    (goto-char (or (byte-to-position (+ pos (vlf-adjust-chunk)))
-                   (point-max))))
-  (set-buffer-modified-p nil)
-  (set-visited-file-modtime)
-  (or minimal(vlf-update-buffer-name)))
-
-(defun vlf-move-to-chunk (start end &optional minimal)
-  "Move to chunk determined by START END.
-When given MINIMAL flag, skip non important operations."
-  (or (verify-visited-file-modtime (current-buffer))
-      (setq vlf-file-size (vlf-get-file-size buffer-file-name)))
-  (setq vlf-start-pos (max 0 start)
-        vlf-end-pos (min end vlf-file-size))
-  (let ((inhibit-read-only t)
-        (pos (position-bytes (point))))
-    (erase-buffer)
-    (insert-file-contents buffer-file-name nil
-                          vlf-start-pos vlf-end-pos)
-    (goto-char (or (byte-to-position (+ pos (vlf-adjust-chunk)))
-                   (point-max))))
-  (set-buffer-modified-p nil)
-  (set-visited-file-modtime)
-  (or minimal (vlf-update-buffer-name)))
-
-(defun vlf-adjust-chunk ()
-  "Adjust chunk beginning until content can be properly decoded.
-Return number of bytes moved back for this to happen."
-  (let ((shift 0)
-        (chunk-size (- vlf-end-pos vlf-start-pos)))
-    (while (and (not (zerop vlf-start-pos))
-                (< shift 4)
-                (/= chunk-size
-                    (length (encode-coding-region
-                             (point-min) (point-max)
-                             buffer-file-coding-system t))))
-      (setq shift (1+ shift)
-            vlf-start-pos (1- vlf-start-pos)
-            chunk-size (1+ chunk-size))
-      (let ((inhibit-read-only t))
-        (erase-buffer)
-        (insert-file-contents buffer-file-name nil
-                              vlf-start-pos vlf-end-pos)))
-    (set-buffer-modified-p nil)
-    shift))
-
-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-;;; search
-
-(defun vlf-re-search (regexp count backward batch-step)
-  "Search for REGEXP COUNT number of times forward or BACKWARD.
-BATCH-STEP is amount of overlap between successive chunks."
-  (assert (< 0 count))
-  (let* ((match-chunk-start vlf-start-pos)
-         (match-chunk-end vlf-end-pos)
-         (match-start-pos (+ vlf-start-pos (position-bytes (point))))
-         (match-end-pos match-start-pos)
-         (to-find count)
-         (reporter (make-progress-reporter
-                    (concat "Searching for " regexp "...")
-                    (if backward
-                        (- vlf-file-size vlf-end-pos)
-                      vlf-start-pos)
-                    vlf-file-size)))
-    (unwind-protect
-        (catch 'end-of-file
-          (if backward
-              (while (not (zerop to-find))
-                (cond ((re-search-backward regexp nil t)
-                       (setq to-find (1- to-find)
-                             match-chunk-start vlf-start-pos
-                             match-chunk-end vlf-end-pos
-                             match-start-pos (+ vlf-start-pos
-                                                (position-bytes
-                                                 (match-beginning 0)))
-                             match-end-pos (+ vlf-start-pos
-                                              (position-bytes
-                                               (match-end 0)))))
-                      ((zerop vlf-start-pos)
-                       (throw 'end-of-file nil))
-                      (t (let ((batch-move (- vlf-start-pos
-                                              (- vlf-batch-size
-                                                 batch-step))))
-                           (vlf-move-to-batch
-                            (if (< match-start-pos batch-move)
-                                (- match-start-pos vlf-batch-size)
-                              batch-move) t))
-                         (goto-char (if (< match-start-pos
-                                           vlf-end-pos)
-                                        (or (byte-to-position
-                                             (- match-start-pos
-                                                vlf-start-pos))
-                                            (point-max))
-                                      (point-max)))
-                         (progress-reporter-update
-                          reporter (- vlf-file-size
-                                      vlf-start-pos)))))
-            (while (not (zerop to-find))
-              (cond ((re-search-forward regexp nil t)
-                     (setq to-find (1- to-find)
-                           match-chunk-start vlf-start-pos
-                           match-chunk-end vlf-end-pos
-                           match-start-pos (+ vlf-start-pos
-                                              (position-bytes
-                                               (match-beginning 0)))
-                           match-end-pos (+ vlf-start-pos
-                                            (position-bytes
-                                             (match-end 0)))))
-                    ((= vlf-end-pos vlf-file-size)
-                     (throw 'end-of-file nil))
-                    (t (let ((batch-move (- vlf-end-pos batch-step)))
-                         (vlf-move-to-batch
-                          (if (< batch-move match-end-pos)
-                              match-end-pos
-                            batch-move) t))
-                       (goto-char (if (< vlf-start-pos match-end-pos)
-                                      (or (byte-to-position
-                                           (- match-end-pos
-                                              vlf-start-pos))
-                                          (point-min))
-                                    (point-min)))
-                       (progress-reporter-update reporter
-                                                 vlf-end-pos)))))
-          (progress-reporter-done reporter))
-      (if backward
-          (vlf-goto-match match-chunk-start match-chunk-end
-                           match-end-pos match-start-pos
-                           count to-find)
-        (vlf-goto-match match-chunk-start match-chunk-end
-                         match-start-pos match-end-pos
-                         count to-find)))))
-
-(defun vlf-goto-match (match-chunk-start match-chunk-end
-                                          match-pos-start
-                                          match-pos-end
-                                          count to-find)
-  "Move to MATCH-CHUNK-START MATCH-CHUNK-END surrounding \
-MATCH-POS-START and MATCH-POS-END.
-According to COUNT and left TO-FIND, show if search has been
-successful.  Return nil if nothing found."
-  (if (= count to-find)
-      (progn (vlf-move-to-chunk match-chunk-start match-chunk-end)
-             (goto-char (or (byte-to-position (- match-pos-start
-                                                 vlf-start-pos))
-                            (point-max)))
-             (message "Not found")
-             nil)
-    (let ((success (zerop to-find)))
-      (if success
-          (vlf-update-buffer-name)
-        (vlf-move-to-chunk match-chunk-start match-chunk-end))
-      (let* ((match-end (or (byte-to-position (- match-pos-end
-                                                 vlf-start-pos))
-                            (point-max)))
-             (overlay (make-overlay (byte-to-position
-                                     (- match-pos-start
-                                        vlf-start-pos))
-                                    match-end)))
-        (overlay-put overlay 'face 'match)
-        (unless success
-          (goto-char match-end)
-          (message "Moved to the %d match which is last"
-                   (- count to-find)))
-        (sit-for 0.1)
-        (delete-overlay overlay)
-        t))))
-
-(defun vlf-re-search-forward (regexp count)
-  "Search forward for REGEXP prefix COUNT number of times.
-Search is performed chunk by chunk in `vlf-batch-size' memory."
-  (interactive (list (read-regexp "Search whole file"
-                                  (if regexp-history
-                                      (car regexp-history)))
-                     (or current-prefix-arg 1)))
-  (vlf-re-search regexp count nil (/ vlf-batch-size 8)))
-
-(defun vlf-re-search-backward (regexp count)
-  "Search backward for REGEXP prefix COUNT number of times.
-Search is performed chunk by chunk in `vlf-batch-size' memory."
-  (interactive (list (read-regexp "Search whole file backward"
-                                  (if regexp-history
-                                      (car regexp-history)))
-                     (or current-prefix-arg 1)))
-  (vlf-re-search regexp count t (/ vlf-batch-size 8)))
-
-(defun vlf-goto-line (n)
-  "Go to line N.  If N is negative, count from the end of file."
-  (interactive "nGo to line: ")
-  (let ((start-pos vlf-start-pos)
-        (end-pos vlf-end-pos)
-        (pos (point))
-        (success nil))
-    (unwind-protect
-        (if (< 0 n)
-            (progn (vlf-beginning-of-file)
-                   (goto-char (point-min))
-                   (setq success (vlf-re-search "[\n\C-m]" (1- n)
-                                                 nil 0)))
-          (vlf-end-of-file)
-          (goto-char (point-max))
-          (setq success (vlf-re-search "[\n\C-m]" (- n) t 0)))
-      (if success
-          (message "Onto line %s" n)
-        (vlf-move-to-chunk start-pos end-pos)
-        (goto-char pos)))))
-
-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-;;; occur
-
-(defvar vlf-occur-mode-map
-  (let ((map (make-sparse-keymap)))
-    (define-key map "n" 'vlf-occur-next-match)
-    (define-key map "p" 'vlf-occur-prev-match)
-    (define-key map "\C-m" 'vlf-occur-visit)
-    (define-key map [mouse-1] 'vlf-occur-visit)
-    (define-key map "o" 'vlf-occur-show)
-    map)
-  "Keymap for command `vlf-occur-mode'.")
-
-(define-derived-mode vlf-occur-mode special-mode "VLF[occur]"
-  "Major mode for showing occur matches of VLF opened files.")
-
-(defun vlf-occur-next-match ()
-  "Move cursor to next match."
-  (interactive)
-  (if (eq (get-char-property (point) 'face) 'match)
-      (goto-char (next-single-property-change (point) 'face)))
-  (goto-char (or (text-property-any (point) (point-max) 'face 'match)
-                 (text-property-any (point-min) (point)
-                                    'face 'match))))
-
-(defun vlf-occur-prev-match ()
-  "Move cursor to previous match."
-  (interactive)
-  (if (eq (get-char-property (point) 'face) 'match)
-      (goto-char (previous-single-property-change (point) 'face)))
-  (while (not (eq (get-char-property (point) 'face) 'match))
-    (goto-char (or (previous-single-property-change (point) 'face)
-                   (point-max)))))
-
-(defun vlf-occur-show (&optional event)
-  "Visit current `vlf-occur' link in a vlf buffer but stay in the \
-occur buffer.  If original VLF buffer has been killed,
-open new VLF session each time.
-EVENT may hold details of the invocation."
-  (interactive (list last-nonmenu-event))
-  (let ((occur-buffer (if event
-                          (window-buffer (posn-window
-                                          (event-end event)))
-                        (current-buffer))))
-    (vlf-occur-visit event)
-    (pop-to-buffer occur-buffer)))
-
-(defun vlf-occur-visit (&optional event)
-  "Visit current `vlf-occur' link in a vlf buffer.
-If original VLF buffer has been killed,
-open new VLF session each time.
-EVENT may hold details of the invocation."
-  (interactive (list last-nonmenu-event))
-  (when event
-    (set-buffer (window-buffer (posn-window (event-end event))))
-    (goto-char (posn-point (event-end event))))
-  (let* ((pos (point))
-         (pos-relative (- pos (line-beginning-position) 1))
-         (file (get-char-property pos 'file)))
-    (if file
-        (let ((chunk-start (get-char-property pos 'chunk-start))
-              (chunk-end (get-char-property pos 'chunk-end))
-              (buffer (get-char-property pos 'buffer))
-              (match-pos (+ (get-char-property pos 'line-pos)
-                            pos-relative)))
-          (or (buffer-live-p buffer)
-              (let ((occur-buffer (current-buffer)))
-                (setq buffer (vlf file))
-                (switch-to-buffer occur-buffer)))
-          (pop-to-buffer buffer)
-          (if (buffer-modified-p)
-              (cond ((and (= vlf-start-pos chunk-start)
-                          (= vlf-end-pos chunk-end))
-                     (goto-char match-pos))
-                    ((y-or-n-p "VLF buffer has been modified.  \
-Really jump to new chunk? ")
-                     (vlf-move-to-chunk chunk-start chunk-end)
-                     (goto-char match-pos)))
-            (vlf-move-to-chunk chunk-start chunk-end)
-            (goto-char match-pos))))))
-
-(defun vlf-occur (regexp)
-  "Make whole file occur style index for REGEXP.
-Prematurely ending indexing will still show what's found so far."
-  (interactive (list (read-regexp "List lines matching regexp"
-                                  (if regexp-history
-                                      (car regexp-history)))))
-  (let ((start-pos vlf-start-pos)
-        (end-pos vlf-end-pos)
-        (pos (point)))
-    (vlf-beginning-of-file)
-    (goto-char (point-min))
-    (unwind-protect (vlf-build-occur regexp)
-      (vlf-move-to-chunk start-pos end-pos)
-      (goto-char pos))))
-
-(defun vlf-build-occur (regexp)
-  "Build occur style index for REGEXP."
-  (let ((line 1)
-        (last-match-line 0)
-        (last-line-pos (point-min))
-        (file buffer-file-name)
-        (total-matches 0)
-        (match-end-pos (+ vlf-start-pos (position-bytes (point))))
-        (occur-buffer (generate-new-buffer
-                       (concat "*VLF-occur " (file-name-nondirectory
-                                               buffer-file-name)
-                               "*")))
-        (line-regexp (concat "\\(?5:[\n\C-m]\\)\\|\\(?10:"
-                             regexp "\\)"))
-        (batch-step (/ vlf-batch-size 8))
-        (end-of-file nil)
-        (reporter (make-progress-reporter
-                   (concat "Building index for " regexp "...")
-                   vlf-start-pos vlf-file-size)))
-    (unwind-protect
-        (progn
-          (while (not end-of-file)
-            (if (re-search-forward line-regexp nil t)
-                (progn
-                  (setq match-end-pos (+ vlf-start-pos
-                                         (position-bytes
-                                          (match-end 0))))
-                  (if (match-string 5)
-                      (setq line (1+ line) ; line detected
-                            last-line-pos (point))
-                    (let* ((chunk-start vlf-start-pos)
-                           (chunk-end vlf-end-pos)
-                           (vlf-buffer (current-buffer))
-                           (line-pos (line-beginning-position))
-                           (line-text (buffer-substring
-                                       line-pos (line-end-position))))
-                      (with-current-buffer occur-buffer
-                        (unless (= line last-match-line) ;new match line
-                          (insert "\n:") ; insert line number
-                          (let* ((overlay-pos (1- (point)))
-                                 (overlay (make-overlay
-                                           overlay-pos
-                                           (1+ overlay-pos))))
-                            (overlay-put overlay 'before-string
-                                         (propertize
-                                          (number-to-string line)
-                                          'face 'shadow)))
-                          (insert (propertize line-text ; insert line
-                                              'file file
-                                              'buffer vlf-buffer
-                                              'chunk-start chunk-start
-                                              'chunk-end chunk-end
-                                              'mouse-face '(highlight)
-                                              'line-pos line-pos
-                                              'help-echo
-                                              (format "Move to line %d"
-                                                      line))))
-                        (setq last-match-line line
-                              total-matches (1+ total-matches))
-                        (let ((line-start (1+
-                                           (line-beginning-position)))
-                              (match-pos (match-beginning 10)))
-                          (add-text-properties ; mark match
-                           (+ line-start match-pos (- last-line-pos))
-                           (+ line-start (match-end 10)
-                              (- last-line-pos))
-                           (list 'face 'match
-                                 'help-echo
-                                 (format "Move to match %d"
-                                         total-matches))))))))
-              (setq end-of-file (= vlf-end-pos vlf-file-size))
-              (unless end-of-file
-                (let ((batch-move (- vlf-end-pos batch-step)))
-                  (vlf-move-to-batch (if (< batch-move match-end-pos)
-                                          match-end-pos
-                                        batch-move) t))
-                (goto-char (if (< vlf-start-pos match-end-pos)
-                               (or (byte-to-position (- match-end-pos
-                                                        vlf-start-pos))
-                                   (point-min))
-                             (point-min)))
-                (setq last-match-line 0
-                      last-line-pos (line-beginning-position))
-                (progress-reporter-update reporter vlf-end-pos))))
-          (progress-reporter-done reporter))
-      (if (zerop total-matches)
-          (progn (with-current-buffer occur-buffer
-                   (set-buffer-modified-p nil))
-                 (kill-buffer occur-buffer)
-                 (message "No matches for \"%s\"" regexp))
-        (with-current-buffer occur-buffer
-          (goto-char (point-min))
-          (insert (propertize
-                   (format "%d matches from %d lines for \"%s\" \
-in file: %s" total-matches line regexp file)
-                   'face 'underline))
-          (set-buffer-modified-p nil)
-          (forward-char 2)
-          (vlf-occur-mode))
-        (display-buffer occur-buffer)))))
-
-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-;;; editing
-
-(defvar vlf-edit-mode-map
-  (let ((map (make-sparse-keymap)))
-    (set-keymap-parent map text-mode-map)
-    (define-key map "\C-c\C-c" 'vlf-write)
-    (define-key map "\C-c\C-q" 'vlf-discard-edit)
-    (define-key map "\C-v" vlf-mode-map)
-    map)
-  "Keymap for command `vlf-edit-mode'.")
-
-(define-derived-mode vlf-edit-mode vlf-mode "VLF[edit]"
-  "Major mode for editing large file chunks."
-  (setq buffer-read-only nil)
-  (buffer-enable-undo)
-  (message (substitute-command-keys
-            "Editing: Type \\[vlf-write] to write chunk \
-or \\[vlf-discard-edit] to discard changes.")))
-
-(defun vlf-discard-edit ()
-  "Discard edit and refresh chunk from file."
-  (interactive)
-  (set-buffer-modified-p nil)
-  (vlf-move-to-chunk vlf-start-pos vlf-end-pos)
-  (vlf-mode)
-  (message "Switched to VLF mode."))
-
-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-;;; saving
-
-(defun vlf-write ()
-  "Write current chunk to file.  Always return true to disable save.
-If changing size of chunk shift remaining file content."
+  (vlf-verify-size)
+  (let* ((start (max 0 start))
+         (end (min (+ start vlf-batch-size) vlf-file-size)))
+    (if (= vlf-file-size end)          ; re-adjust start
+        (setq start (max 0 (- end vlf-batch-size))))
+    (vlf-move-to-chunk start end minimal)))
+
+(defun vlf-next-batch-from-point ()
+  "Display batch of file data starting from current point."
   (interactive)
-  (when (and (buffer-modified-p)
-             (or (verify-visited-file-modtime (current-buffer))
-                 (y-or-n-p "File has changed since visited or saved.  \
-Save anyway? ")))
-    (let ((pos (point))
-          (size-change (- vlf-end-pos vlf-start-pos
-                          (length (encode-coding-region
-                                   (point-min) (point-max)
-                                   buffer-file-coding-system t)))))
-      (cond ((zerop size-change)
-             (write-region nil nil buffer-file-name vlf-start-pos t))
-            ((< 0 size-change)
-             (vlf-file-shift-back size-change))
-            (t (vlf-file-shift-forward (- size-change))))
-      (vlf-move-to-chunk vlf-start-pos vlf-end-pos)
-      (goto-char pos))
-    (vlf-mode))
-  t)
-
-(defun vlf-file-shift-back (size-change)
-  "Shift file contents SIZE-CHANGE bytes back."
-  (write-region nil nil buffer-file-name vlf-start-pos t)
-  (buffer-disable-undo)
-  (let ((read-start-pos vlf-end-pos)
-        (coding-system-for-write 'no-conversion)
-        (reporter (make-progress-reporter "Adjusting file content..."
-                                          vlf-end-pos
-                                          vlf-file-size)))
-    (while (vlf-shift-batch read-start-pos (- read-start-pos
-                                               size-change))
-      (setq read-start-pos (+ read-start-pos vlf-batch-size))
-      (progress-reporter-update reporter read-start-pos))
-    ;; pad end with space
-    (erase-buffer)
-    (insert-char 32 size-change)
-    (write-region nil nil buffer-file-name (- vlf-file-size
-                                              size-change) t)
-    (progress-reporter-done reporter)))
-
-(defun vlf-shift-batch (read-pos write-pos)
-  "Read `vlf-batch-size' bytes from READ-POS and write them \
-back at WRITE-POS.  Return nil if EOF is reached, t otherwise."
-  (erase-buffer)
-  (or (verify-visited-file-modtime (current-buffer))
-      (setq vlf-file-size (vlf-get-file-size buffer-file-name)))
-  (let ((read-end (+ read-pos vlf-batch-size)))
-    (insert-file-contents-literally buffer-file-name nil
-                                    read-pos
-                                    (min vlf-file-size read-end))
-    (write-region nil nil buffer-file-name write-pos 0)
-    (< read-end vlf-file-size)))
-
-(defun vlf-file-shift-forward (size-change)
-  "Shift file contents SIZE-CHANGE bytes forward.
-Done by saving content up front and then writing previous batch."
-  (buffer-disable-undo)
-  (let ((size (+ vlf-batch-size size-change))
-        (read-pos vlf-end-pos)
-        (write-pos vlf-start-pos)
-        (reporter (make-progress-reporter "Adjusting file content..."
-                                          vlf-start-pos
-                                          vlf-file-size)))
-    (when (vlf-shift-batches size read-pos write-pos t)
-      (setq write-pos (+ read-pos size-change)
-            read-pos (+ read-pos size))
-      (progress-reporter-update reporter write-pos)
-      (let ((coding-system-for-write 'no-conversion))
-        (while (vlf-shift-batches size read-pos write-pos nil)
-          (setq write-pos (+ read-pos size-change)
-                read-pos (+ read-pos size))
-          (progress-reporter-update reporter write-pos))))
-    (progress-reporter-done reporter)))
-
-(defun vlf-shift-batches (size read-pos write-pos hide-read)
-  "Append SIZE bytes of file starting at READ-POS.
-Then write initial buffer content to file at WRITE-POS.
-If HIDE-READ is non nil, temporarily hide literal read content.
-Return nil if EOF is reached, t otherwise."
-  (or (verify-visited-file-modtime (current-buffer))
-      (setq vlf-file-size (vlf-get-file-size buffer-file-name)))
-  (let ((read-more (< read-pos vlf-file-size))
-        (start-write-pos (point-min))
-        (end-write-pos (point-max)))
-    (when read-more
-      (goto-char end-write-pos)
-      (insert-file-contents-literally buffer-file-name nil read-pos
-                                      (min vlf-file-size (+ read-pos
-                                                             size))))
-    ;; write
-    (if hide-read ; hide literal region if user has to choose encoding
-        (narrow-to-region start-write-pos end-write-pos))
-    (write-region start-write-pos end-write-pos
-                  buffer-file-name write-pos 0)
-    (delete-region start-write-pos end-write-pos)
-    (if hide-read (widen))
-    read-more))
+  (let ((start (+ vlf-start-pos (position-bytes (point)) -1)))
+    (vlf-move-to-chunk start (+ start vlf-batch-size)))
+  (goto-char (point-min)))
 
 (provide 'vlf)