BitClr
BitClr Clear a specified bit in a bit string to a 0 void BitClr(bytePtr, bitNum ); Ptr bytePtr ; address of the byte at the start of bit string long bitNum ; 0-based ID of bit to clear
BitClr clears a specified bit in a bit string to a 0. bytePtr is the address of the first byte of a sequence of bytes.
bitNum identifies the bit to clear. It is 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 BitTst for details.