Bit Test, Set, and Clear Functions: Carbon and POSIX
Don’t mix using the C bitwise operators with the Carbon functions BitTst, BitSet, and BitClr and the POSIX macros setbit, clrbit, isset, and isclr. If you consistently use the Carbon and POSIX functions and avoid the C bitwise operators, your code will function properly. Keep in mind, however, that you must use the Carbon and POSIX functions on the correct kind of data. The Carbon and POSIX functions perform a byte-by-byte traversal, which causes problems on an Intel-based Macintosh when they operate on data types that are larger than 1 byte. You can use these functions only on a pointer to a string of endian-neutral bytes. When you need to perform bit manipulation on integer values you should use functions such as (int32 & (1 << 26)) instead of BitTst(&int32, 5L).
You’ll encounter problems when you use the function BitTst to test for 24-bit mode. For example, the following bit test returns false, which indicates that the process is running in 24-bit mode, or at least that the code is not running in 32-bit mode. The POSIX equivalents perform similarly:
Gestalt(gestaltAddressingModeAttr, &gestaltResult); |
if (!(BitTst(&gestaltResult,31L)) ) /*If 24 bit |
You can use any of the bit testing, setting, and clearing functions if you pass a pointer to data whose byte order is fixed. Used in this way, these functions behave the same on both architectures.
For more information, see the ToolUtils.h header file in the Core Services framework and Mathematical and Logical Utilities Reference.
Last updated: 2007-02-26
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