[Cscope-devel] A dicode compression crash

[Hans-Bernhard B. <br...@ph...>]

Hello, all, 

I've just come across a crash inside putcrossref(), and on debugging it,
found that it was caused by casting a char to (unsigned) and using the
result as an index into dicode1[]. That's not quite correct. The cast must
be to (unsigned char), where as (unsigned) alone implies (unsigned int).
In the case at hand the signed character was -8, which got casted to 2^32
- 8. The expected result was, of course 256 - 8. 

So I changed the datatypes and casts in all relevant places from unsigned
to unsigned char. That fixed the crash nicely.

While being at it, I also streamlined the dicode compression stuff a bit,
using macros so it won't affect the performance. Here's their definition
to go into global.h:

/* and some macros to help using dicodes: */
/* Check if a given pair of chars is compressable as a dicode: */
#define IS_A_DICODE(inchar1, inchar2) \
  (dicode1[(unsigned char)(inchar1)] && dicode2[(unsigned char)(inchar2)])
/* Combine the pair into a dicode */
#define DICODE_COMPRESS(inchar1, inchar2)		\
  ((0200 - 2) + dicode1[(unsigned char)(inchar1)]	\
   + dicode2[(unsigned char)(inchar2)]

And this is what the code using it will now look like (from find.c):

***************
*** 674,681 ****
  		/* compress the string pattern for matching */
  		s = cpattern;
  		for (i = 0; (c = pattern[i]) != '\0'; ++i) {
! 			if (dicode1[c] && dicode2[(unsigned) pattern[i + 1]]) {
! 				c = (0200 - 2) + dicode1[c] + dicode2[(unsigned) pattern[i + 1]];
  				++i;
  			}
  			*s++ = c;
--- 675,682 ----
  		/* compress the string pattern for matching */
  		s = cpattern;
  		for (i = 0; (c = pattern[i]) != '\0'; ++i) {
! 			if (IS_A_DICODE(c, pattern[i + 1])) {
! 				c = DICODE_COMPRESS(c, pattern[i + 1]);
  				++i;
  			}
  			*s++ = c;

Any objections to checking in such a change?

-- 
Hans-Bernhard Broeker (br...@ph...)
Even if all the snow were burnt, ashes would remain.