Fix an off-by-one error in FcLangSetIndex()
This commit fixes a bug that can be reproduced like this: - remove all languages starting with 'a' in fc-lang/Makefile.am (in ORTH's definition); - rebuild fontconfig with this change (-> new fc-lang/fclang.h); - create an FcLangSet 'ls1' that contains at least the first language from fcLangCharSets (i.e., the first *remaining* in lexicographic order); let's assume it is "ba" for the sake of this description; - create an FcLangSet 'ls2' that only contains the language "aa" (any language starting with 'a' should work as well); - check the return value of FcLangSetContains(ls1, ls2); The expected return value is FcFalse, however it is FcTrue if you use the code before this commit. What happens is that FcLangSetIndex() returns 0, because this is the index of the first slot after the not-found language "aa" in fcLangCharSets (since we removed all languages starting with 'a'). However, this index happens to be non-negative, therefore FcLangSetContainsLang() mistakenly infers that the language "aa" was found in fcLangCharSets, and thus calls FcLangSetBitGet(ls1, 0), which returns FcTrue since we've put the first remaining language "ba" in the 'ls1' language set. The "return -low;" statement previously in FcLangSetIndex() was inconsistent with the final return statement. "return -(low+1);" fixes this inconsistency as well as the incorrect behavior described above.
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src/fclang.c
11
src/fclang.c
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@ -505,6 +505,15 @@ bail0:
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return 0;
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}
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/* When the language isn't found, the return value r is such that:
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* 1) r < 0
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* 2) -r -1 is the index of the first language in fcLangCharSets that comes
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* after the 'lang' argument in lexicographic order.
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*
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* The -1 is necessary to avoid problems with language id 0 (otherwise, we
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* wouldn't be able to distinguish between “language found, id is 0” and
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* “language not found, sorts right before the language with id 0”).
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*/
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static int
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FcLangSetIndex (const FcChar8 *lang)
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{
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@ -529,7 +538,7 @@ FcLangSetIndex (const FcChar8 *lang)
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high = fcLangCharSetRanges[firstChar - 'a'].end;
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/* no matches */
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if (low > high)
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return -low; /* next entry after where it would be */
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return -(low+1); /* one past next entry after where it would be */
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}
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while (low <= high)
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