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;;;; svndiff.lisp - encoding copy/insert deltas in svndiff format
(in-package :diff)
(declaim (optimize (debug 3)))
(defun instruction-buffer-length (instlist)
"Compute the length of the instruction buffer for a window containing
the instructions in INSTLIST."
(reduce #'+ instlist :initial-value 0 :key #'instruction-length))
(defun new-data-buffer-length (instlist)
"Compute the length of the new data buffer for a window containing
the instructions in INSTLIST."
(reduce #'+ instlist :initial-value 0
:key #'(lambda (op)
(ecase (svndiff-op-kind op)
(:new-data (svndiff-op-bytes op))
((:copy-source :copy-target) 0)))))
(defun write-svndiff-op (op target instruction-stream data-stream)
(declare (type bytebuf target))
(let ((kind (svndiff-op-kind op))
(offset (svndiff-op-offset op))
(bytes (svndiff-op-bytes op)))
(flet ((encode-copy (insn-byte)
(when (< bytes 64)
(setf insn-byte (logior insn-byte bytes)))
(write-byte insn-byte instruction-stream)
(when (>= bytes 64)
(write-svndiff-integer bytes instruction-stream))
(write-svndiff-integer offset instruction-stream)))
(ecase kind
(:copy-target (encode-copy #x40))
(:copy-source (encode-copy #x00))
(let ((insn-byte #x80)) ; first two bits `10'
(when (< bytes 64)
(setf insn-byte (logior insn-byte bytes)))
(write-byte insn-byte instruction-stream)
(when (>= bytes 64)
(write-svndiff-integer bytes instruction-stream))
(dotimes (i bytes)
(write-byte (aref target (+ i offset))
(defun construct-svndiff-window (source-offset source-len target-len
ops target)
(declare (type bytebuf target))
(let* ((ops-buf-length (instruction-buffer-length ops))
(data-buf-length (new-data-buffer-length ops))
(ops-buffer (make-array ops-buf-length
:element-type '(unsigned-byte 8)
:initial-element 0))
(data-buffer (make-array data-buf-length
:element-type '(unsigned-byte 8)
:initial-element 0))
(ops-stream (make-instance 'byte-buffer-stream :buffer ops-buffer))
(data-stream (make-instance 'byte-buffer-stream :buffer data-buffer)))
(declare (type bytebuf ops-buffer data-buffer))
(dolist (op ops)
(write-svndiff-op op target ops-stream data-stream))
(make-svndiff-window :source-offset source-offset
:source-len source-len
:target-len target-len
:ops ops-buffer
:new-data data-buffer)))
(defun svndiff-integer-length (num)
(if (zerop num)
(nth-value 0 (ceiling (integer-length num) 7))))
(defun instruction-length (op)
"Compute the number of bytes needed to represent OP when it is svndiff
(let ((kind (svndiff-op-kind op))
(offset (svndiff-op-offset op))
(bytes (svndiff-op-bytes op)))
(ecase kind
((:copy-source :copy-target)
(if (< bytes 64)
(1+ (svndiff-integer-length offset))
(+ 1
(svndiff-integer-length offset)
(svndiff-integer-length bytes))))
(if (< bytes 64)
(1+ (svndiff-integer-length bytes)))))))
(defun read-svndiff-integer (stream)
"Reads a svndiff-encoded integer from STREAM."
(let ((int 0)
(byte (read-byte stream))
(data-byte-spec (byte 7 0)))
(setf int (ldb data-byte-spec byte))
(loop while (> byte 127)
do (setf byte (read-byte stream)
int (logior (ash int 7)
(ldb data-byte-spec byte))))
(defun write-svndiff-integer (integer stream)
"Writes the non-negative INTEGER to STREAM using svndiff encoding."
(when (zerop integer)
(write-byte #x00 stream)
(return-from write-svndiff-integer (values)))
(let ((blocks (svndiff-integer-length integer)))
(loop for i downfrom blocks above 0
do (let ((part (ldb (byte 7 (* 7 (1- i))) integer)))
(assert (< part 128))
(unless (= i 1)
(setf part (logior #x80 part)))
(write-byte part stream)))
(defun read-svndiff-window (stream)
"Reads a svndiff window from STREAM."
(let ((source-offset (read-svndiff-integer stream))
(source-len (read-svndiff-integer stream))
(target-len (read-svndiff-integer stream))
(instrs-len (read-svndiff-integer stream))
(new-data-len (read-svndiff-integer stream)))
(let ((instr-bytes (make-array instrs-len
:element-type '(unsigned-byte 8)
:initial-element 0))
(new-data (make-array new-data-len
:element-type '(unsigned-byte 8)
:initial-element 0))
(bytes-read 0))
(declare (type bytebuf instr-bytes new-data))
(setf bytes-read (read-sequence instr-bytes stream))
(unless (= bytes-read instrs-len)
(error "Could not read instructions for svndiff window."))
(setf bytes-read (read-sequence new-data stream))
(unless (= bytes-read new-data-len)
(error "Could not read new data for svndiff window."))
(make-svndiff-window :source-offset source-offset
:source-len source-len
:target-len target-len
:ops instr-bytes
:new-data new-data))))
(defun write-svndiff-window (window stream)
"Writes the svndiff window WINDOW to STREAM."
(let ((source-offset (svndiff-window-source-offset window))
(source-len (svndiff-window-source-len window))
(target-len (svndiff-window-target-len window))
(instr-bytes (svndiff-window-ops window))
(new-data (svndiff-window-new-data window)))
(declare (type (simple-array (unsigned-byte 8) (*)) instr-bytes new-data))
(write-svndiff-integer source-offset stream)
(write-svndiff-integer source-len stream)
(write-svndiff-integer target-len stream)
(write-svndiff-integer (length instr-bytes) stream)
(write-svndiff-integer (length new-data) stream)
(write-sequence instr-bytes stream)
(write-sequence new-data stream)
(defun write-svndiff (windows stream)
"Writes a svndiff document to STREAM using the information in WINDOWS,
which is a list of SVNDIFF-WINDOWs."
;; "SVN\0"
(write-byte #x83 stream)
(write-byte #x86 stream)
(write-byte #x78 stream)
(write-byte #x00 stream)
(dolist (window windows)
(write-svndiff-window window stream)))
;;; high level driver for the whole shebang
(defun compare-files (source-filename target-filename)
"Return a list of svndiff windows describing the differences between
(with-binary-file (source-stream source-filename :input)
(with-binary-file (target-stream target-filename :input)
(let ((context (make-instance 'vdelta-context))
(windows nil))
(do* ((buffer (buffer context))
(source-offset 0)
(source-length (read-sequence buffer source-stream
:start 0 :end +buffer-size+)
(read-sequence buffer source-stream
:start 0 :end +buffer-size+))
(target-length (read-sequence buffer target-stream
:start source-length)
(read-sequence buffer target-stream
:start source-length)))
((zerop target-length) (nreverse windows))
(clrhash (table context))
(setf (source-length context) source-length
(target-start context) source-length
(target-length context) (- target-length source-length))
(initialize-match-table context)
(let* ((ops (calculate-svndiff-ops context)))
(push ops windows))
(incf source-offset source-length))))))
;;; vcdiff encoding stuff
;;; managing the cache. these algorithms are taken directly from the RFC,
;;; with small adjustments from the C-style used therein
(defclass address-cache ()
((near-cache :initarg :near-cache :reader near-cache)
(next-near-slot :initform 0 :reader next-near-slot)
(same-cache :initarg :same-cache :reader same-cache)))
(defun make-address-cache (near-size same-size)
(let ((near-cache (make-array near-size :initial-element 0))
(same-cache (make-array (* 256 same-size :initial-element 0))))
(make-instance 'address-cache
:near-cache near-cache :same-cache same-cache)))
(defun update-cache (address-cache address)
(let ((near-cache-length (length (near-cache address-cache)))
(same-cache-length (length (same-cache address-cache))))
(when (plusp near-cache-length)
(setf (aref (near-cache address-cache) (next-near-slot address-cache))
(setf (next-near-slot address-cache)
(truncate (1+ (next-near-slot address-cache)) near-cache-length)))
(when (plusp same-cache-length)
(setf (aref (same-cache address-cache)
(nth-value 1 (truncate address same-cache-length)))
;;; from the RFC: "attempt to find the address mode that yields the
;;; smallest integer value for the encoded address value, thereby
;;; minimizing the encoded size of the address. the RFC goes on to
;;; note that this best address value is "local" and suggests that more
;;; complex schemes might be able to do better.
(defun encode-address (address-cache address here-p)
(let ((best-encoded-address address)
;; I think when the RFC uses `here', it means `target', and
;; when it uses `self', it means `source'. check this to
;; make sure our intuition is right. why don't they use
;; self-descriptive terms? and can't we already figure this
;; out in an earlier phase?
(best-mode (if here-p :vcd-here :vcd-self)))
(dotimes (i (length (near-cache address-cache)))
(let ((d (- address (aref (near-cache address-cache) i))))
(when (and (not (minusp d)) (< d best-encoded-address))
(setf best-encoded-address d
;; ugh
best-mode (+ i 2)))))
(let ((d (nth-value 1 (truncate address
(* 256 (length (same-cache address-cache)))))))
(when (and (plusp (length (same-cache address-cache)))
(= addr
(aref (same-cache address-cache) d)))
(setf best-encoded-address d
best-mode (+ (length (near-cache address-cache)) 2 (truncate d 256))))
(update-cache address-cache address)
(values best-encoded-address best-mode))))
(defun decode-address (address-cache address mode)
(let ((decoded-address 0))
((eq mode :vcd-self) (setf decoded-address
(fetch-copy-address-integer #|wherever|#)))
((eq mode :vcd-here) (setf decoded-address
(- address (fetch-copy-address-integer #|wherever|#))))
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