BitTst

BitTst Determine state of a bit in a bit string

#include <ToolUtils.h> Toolbox Utilities

Boolean BitTst(bytePtr, bitNum );

Ptr bytePtr ; address of the byte at the start of "bit string

long bitNum ; 0-based ID of bit to check

returns Is the bit a 1?

This returns TRUE if a specified bit is a 1; FALSE if it is a 0.

bytePtr is the address of the first byte of a sequence of bytes.

bitNum identifies the bit to test, as a positive offset from the first bit in the

byte addressed by bytePtr.. Bits are identified by a logical mapping

( matching that used for screen pixels), rather than the normal

high-to-low numbering used in CPU operations. See Notes, below.

Returns: a Boolean value indicating the state of the bit. It will be one of:

FALSE Bit bitNum is 0 (by convention, white or OFF)

TRUE Bit bitNum is 1 (black or ON)

Notes: This function does some address arithmetic to overcome difficulties

surrounding MC68000 even-address restrictions and the normal

right-to-left bit ordering. The result is that you can treat any area of

memory (as much as 16 Mega bytes) as a string of sequentially- numbered

bits.

Any bit in the bit string can be accessed individually via BitTst, BitSet,

and BitClr. Other Toolbox BitXxx functions apply to bitwise operations

between long integers and not relevant for C programmers.

Referenced by (18):