bitmap_pos_to_ord — find ordinal of set bit at given position in bitmap


int bitmap_pos_to_ord (const unsigned long * buf,
 unsigned int pos,
 unsigned int nbits);


const unsigned long * buf

pointer to a bitmap

unsigned int pos

a bit position in buf (0 <= pos < nbits)

unsigned int nbits

number of valid bit positions in buf


Map the bit at position pos in buf (of length nbits) to the ordinal of which set bit it is. If it is not set or if pos is not a valid bit position, map to -1.

If for example, just bits 4 through 7 are set in buf, then pos values 4 through 7 will get mapped to 0 through 3, respectively, and other pos values will get mapped to -1. When pos value 7 gets mapped to (returns) ord value 3 in this example, that means that bit 7 is the 3rd (starting with 0th) set bit in buf.

The bit positions 0 through bits are valid positions in buf.