201.c

#include<stdio.h>
#include<stdlib.h>

intrangeBitwiseAnd_1(intm, intn) {
unsignedans=m;
unsignedk;
unsignedone_index=0; /* first one's index */
unsignedzero_index=0; /* first zero after the first one */

while (one_index<31) {
while (one_index<31&& (ans& (1 << one_index)) ==0){
one_index++;
 }

zero_index=one_index;
while (zero_index<32&&ans& (1 << zero_index)) {
zero_index++;
 }

if (zero_index>one_index) {
/* nearest number to make first one to zero */
k= (ans | (1 << zero_index)) >> zero_index;
k=k << zero_index;

if (k>n) returnans; /* rest numbers are useless */
ans &= k;
 }

if (ans==0) return0; /* it's pointless to continue looping */
one_index++;
 }

returnans;
}

/** 
 * algorithm comes from http://math.stackexchange.com/a/1073544
 */
intrangeBitwiseAnd(intm, intn) {
intk=30;
unsignedans=m&n;
/* check kth bit, if they are different, set remain bits to zero */
while (k>0&& (m& (1 << k)) == (n& (1 << k))){
k--;
 }
/* there is no need to check 0th bit, we already do m AND n*/
ans >>= k;
ans <<= k;
returnans;
}

intmain() {
/* should be 0 */
printf("%d\n", rangeBitwiseAnd(2, 4));

/* should be 2147483644 */
printf("%d\n", rangeBitwiseAnd(2147483645, 2147483647));

/* should be 2147483647 */
printf("%d\n", rangeBitwiseAnd(2147483647, 2147483647));

/* should be 0 */
printf("%d\n", rangeBitwiseAnd(700000000, 2147483641));

/* should be 0 */
printf("%d\n", rangeBitwiseAnd(3, 4));

return0;
}