Efficient bit twiddeling in C

To set or clear a bit within a byte variable based upon a bit in the same or other byte variable try:

(byte2 &= ~BITMASK2), (byte1 & BITMASK1) ? (byte2 |= BITMASK2) : 0;

Which could be encapsulated into a macro:

#define setmask(b1, m1, b2, m2) (((b2) &= ~(m2)), ((b1) & (m1)) ? ((b2) |= (m2)) : 0)

which you would use thusly:

        setmask(byte1, BITMASK1, byte2, BITMASK2);

The result for the PIC is:

        bcf     _byte2,3
        btfsc   _byte1,2
        bsf     _byte2,3

Which is very effecient. If you don't want to clear the bit first (e.g. if it was a port pin) then it would be:

(!(byte1 & BITMASK1) ? (byte2 &= ~BITMASK2) : 0), (byte1 & BITMASK1) ? (byte2 |= BITMASK2) : 0;

PIC - Bit operations@

file: /techref/language/ccpp/bittwid.htm, 1KB, , updated: 2008/3/19 02:23, local time: 2008/7/4 22:11,

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