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Inside Macintosh: Operating System Utilities /
Chapter 3 - Mathematical and Logical Utilities / Mathematical and Logical Utilities Reference
Routines / Testing and Setting Bits


You can use the BitClr procedure to clear a particular bit.

PROCEDURE BitClr (bytePtr: Ptr; bitNum: LongInt);
A pointer to a byte in memory.
The bit to be cleared, specified as a positive offset from the high-order bit of the byte pointed to by the bytePtr parameter. The bit being cleared need not be in the same byte pointed to by bytePtr.
The BitClr procedure clears (to a value of 0) the bit specified by the bytePtr and bitNum parameters.

The bit-numbering scheme used by the BitClr procedure is the opposite of MC680x0 bit numbering. To convert an MC680x0 bit number to the format required by the BitClr procedure, subtract the MC680x0 bit number from the highest bit number.

For an example of the use of the BitClr procedure, see page 3-16. For more information about reversed bit-numbering, see "Reversed Bit-Numbering" on page 3-7.

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6 JUL 1996

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