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ICU-8096 make U_MAX_PTR(base) conform to C++ standard where possible

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X-SVN-Rev: 30021
This commit is contained in:
Markus Scherer 2011-05-04 15:33:44 +00:00
parent af43054b4e
commit 9d4af09bea
1 changed files with 18 additions and 14 deletions
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32
icu4c/source/common/putilimp.h
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@ -253,7 +253,7 @@ U_INTERNAL void * U_EXPORT2 uprv_maximumPtr(void *base);
* - return the largest possible pointer greater than base
* - return a valid pointer according to the machine architecture (AS/400, 64-bit, etc.)
* - avoid wrapping around at high addresses
* - make sure that the returned pointer is not farther from base than 0x7fffffff
* - make sure that the returned pointer is not farther from base than 0x7fffffff bytes
*
* @param base The beginning of a buffer to find the maximum offset from
* @internal
@ -264,23 +264,27 @@ U_INTERNAL void * U_EXPORT2 uprv_maximumPtr(void *base);
# define U_MAX_PTR(base) ((void *)0x7fffffff)
# elif defined(OS400)
# define U_MAX_PTR(base) uprv_maximumPtr((void *)base)
# elif defined(__GNUC__) && __GNUC__ >= 4
/*
* Due to a compiler optimization bug, gcc 4 causes test failures when doing
* this math arithmetic on pointers on some platforms. It seems like the
* pointers are considered signed instead of unsigned. The uintptr_t type
* isn't available on all platforms (i.e MSVC 6) and pointers aren't always
* a scalar value (i.e. i5/OS see uprv_maximumPtr function).
*/
# elif 0
/*
* For platforms where pointers are scalar values (which is normal, but unlike i5/OS)
* but that do not define uintptr_t.
*
* However, this does not work on modern compilers:
* The C++ standard does not define pointer overflow, and allows compilers to
* assume that p+u>p for any pointer p and any integer u>0.
* Thus, modern compilers optimize away the ">" comparison.
* (See ICU tickets #7187 and #8096.)
*/
# define U_MAX_PTR(base) \
((void *)(((char *)(base)+0x7fffffffu) > (char *)(base) \
? ((char *)(base)+0x7fffffffu) \
: (char *)-1))
# else
/* Default version. C++ standard compliant for scalar pointers. */
# define U_MAX_PTR(base) \
((void *)(((uintptr_t)(base)+0x7fffffffu) > (uintptr_t)(base) \
? ((uintptr_t)(base)+0x7fffffffu) \
: (uintptr_t)-1))
# else
# define U_MAX_PTR(base) \
((char *)(((char *)(base)+0x7fffffffu) > (char *)(base) \
? ((char *)(base)+0x7fffffffu) \
: (char *)-1))
# endif
#endif