Class file has a larger 4 byte value then emacs can handle

Eric Warmenhoven <[email protected]> Thu, 17 Sep 2009 14:03:15 -0700

Newsgroups	gmane.emacs.jdee.devel
Message-ID	<[email protected]>

Hello,

In one of the java files in the project I'm working on, there is a
switch statement that uses very large values (0x70000000 - 0x7000000f)
for the cases. javac turns it into a tableswitch opcode with the low and
high values "larger than emacs can handle".

Because tableswitch is only going to be used if the values are somewhat
close together, there's really no reason for this error to happen here.

I've attached a diff (against svn branches/2.4.0) that changes the
tableswitch handling so that instead of getting the low and high values
independently and subtracting, it will get both values at the same time
and do the subtraction in line with reconstructing a 4-byte value.

Thanks,
Eric

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tableswitch.diff (text/x-diff, 2.7 KB)

*** /home/ewarmenhoven/jde-parse-class.el	Thu Sep 17 14:01:29 2009
--- /home/ewarmenhoven/jde-parse-class-mod.el	Fri Sep 11 15:33:13 2009
***************
*** 328,336 ****
  		;; The second mod is to make sure on an offset of 4 we really don't skip anything
  		(forward-char (mod (- 4 (mod (- (point) begin-point) 4)) 4))
  		(forward-char 4)  ;; we don't care about default
! 		(let ((low (jde-parse-class-get-next-4-bytes-as-signed))
! 		      (high (jde-parse-class-get-next-4-bytes-as-signed)))
! 		  (forward-char (* 4 (+ (- high low) 1)))))
  	      ((eq opcode-val 'lookupswitch)
  		(forward-char (mod (- 4 (mod (- (point) begin-point) 4)) 4))
  		(forward-char 4)
--- 328,335 ----
  		;; The second mod is to make sure on an offset of 4 we really don't skip anything
  		(forward-char (mod (- 4 (mod (- (point) begin-point) 4)) 4))
  		(forward-char 4)  ;; we don't care about default
! 		(let ((diff (jde-parse-class-diff-next-two-4-bytes-as-signed)))
! 		  (forward-char (* 4 (+ diff 1)))))
  	      ((eq opcode-val 'lookupswitch)
  		(forward-char (mod (- 4 (mod (- (point) begin-point) 4)) 4))
  		(forward-char 4)
***************
*** 492,498 ****
  (defun jde-parse-class-get-next-4-bytes-as-signed (&optional ignore-large-val)
    (let ((db1 (jde-parse-class-get-next-2-bytes))
  	(db2 (jde-parse-class-get-next-2-bytes)))
!     (if (> (logand 32768 db1) 0)  ;; if it's high-bit is set, then it's negative.
        (if (> db1 63488)
  	(- (+ 1 (+ (* (- 65535 db1) 65536) (- 65535 db2))))
  	(if ignore-large-val
--- 491,497 ----
  (defun jde-parse-class-get-next-4-bytes-as-signed (&optional ignore-large-val)
    (let ((db1 (jde-parse-class-get-next-2-bytes))
  	(db2 (jde-parse-class-get-next-2-bytes)))
!     (if (> (logand 32768 db1) 0)  ;; if its high-bit is set, then it's negative.
        (if (> db1 63488)
  	(- (+ 1 (+ (* (- 65535 db1) 65536) (- 65535 db2))))
  	(if ignore-large-val
***************
*** 500,505 ****
--- 499,514 ----
  	  (error "Class file has an unsigned int who is smaller than emacs can handle")))
        (jde-parse-class-get-4byte (- (point) 4)))))
  
+ (defun jde-parse-class-diff-next-two-4-bytes-as-signed ()
+   (let ((low1 (jde-parse-class-get-next-2-bytes))
+         (low2 (jde-parse-class-get-next-2-bytes))
+         (high1 (jde-parse-class-get-next-2-bytes))
+         (high2 (jde-parse-class-get-next-2-bytes)))
+     (if (and (> (logand 32768 low1) 0)
+              (<= (logand 32768 high1) 0))
+         (+ (* 65536 (- (+ high1 65535) low1)) (- (+ high2 65536) low2))
+       (+ (* 65535 (- high1 low1)) (- high2 low2)))))
+ 
  (defun jde-parse-class-get-next-4-bytes (&optional ignore-large-val)
    (do-and-advance-chars 4
      (jde-parse-class-get-4byte (point) ignore-large-val)))

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