first commit with bmpln.c file to this repo

Author: sunitgopal

bmpln.c

@@ -0,0 +1,232 @@
+#include <stdio.h>
+
+int isOdd(unsigned int x){ // Returns 1 if Odd, 0 if even // printf("%s", isOdd(a) ? "Odd" : "Even");
+ 
+ if(x & 1u){
+ return 1;
+ }
+ return 0;
+}
+
+/*****************************************************************************************************/
+
+int areOppSigns(int x, int y){ // Returns 1 if Opp, 0 if Same
+
+
+ if ((x ^ y) < 0){ // Opp sign
+ return 1;
+ }
+ return 0;
+}
+
+/*****************************************************************************************************/
+
+/********** Add 1 to an integer ***************/
+
+// Use the fact that 2's complement of a number (how -number is stored) is (1+inv(number))
+// -x = ~x + 1;
+// -~x = 1+x
+
+int addOne(int x){ // Returns result
+
+ int ans; 
+ ans = -(~x); 
+ return ans;
+}
+
+/*****************************************************************************************************/
+
+/******** Swap two numbers w/o third variable **********/
+
+// x ^ x = 0
+// x ^ 0 = x
+
+void Swap(int * x, int * y){
+
+ *x = *x ^ *y;
+ *y = *x ^ *y;
+ *x = *x ^ *y;
+
+ return;
+}
+
+/*****************************************************************************************************/
+
+/******* Turn off kth bit in a number ***************/
+
+// make a MACRO that takes in the position k, and makes a MASK for that position
+
+#define MASK(k) (1u << (k))
+
+int kthOff (int x, int k){
+
+ int ans;
+ ans = x & (~(MASK(k)));
+ 
+ return ans;
+}
+
+/*****************************************************************************************************/
+
+/******* Turn on kth bit in a number ***************/
+
+//#ifndef MASK(k) // ifndef doesn't work on MACROFUNCTION ?
+//#define MASK(k) (1u << k)
+
+//#endif
+
+// using the same MACROFUNCTION created above
+
+void kthOn (int* x, int k){
+
+ *x |= MASK(k);
+
+ return; 
+}
+
+/*****************************************************************************************************/
+
+/******* Check if kth bit is set in a number ***************/
+
+// using the same MACROFUNCTION created above
+
+int iskthSet(int x, int k){
+
+ return (x & MASK(k));
+}
+
+/*****************************************************************************************************/
+
+/******* Toggle the kth bit ***************/
+
+// using the same MACROFUNCTION created above
+
+void togglekth(int* x, int k){
+
+ *x ^= MASK(k);
+}
+
+/*****************************************************************************************************/
+
+/******* Unset the righmost-set bit ***************/
+
+// performing n & (n-1) unsets the rightmost-set-bit in n
+// (n-1) has all the bits AFTER the rightmost-set-bit flipped w.r.t n
+
+int unsetrightmostset (int x){ // Returns result
+
+ return (x & (x-1));
+}
+
+/*****************************************************************************************************/
+
+/******* Check if number is a power of 2 ***************/
+
+// put the righmost-set-bit concept to use
+// pwr of 2 will only have one bit set in total
+// so, if pwrof2, then unsetting that bit should yield 0
+
+int ispwroftwo (int x){ // Returns 1 if true, 0 false
+ 
+ //(x & (x-1)) ? return (0) : return (1); //error: expected expression before return
+
+ if(x&(x-1))
+ return 0;
+ else
+ return 1;
+}
+
+/*****************************************************************************************************/
+
+/******* Find position of the righmost-set-bit ***************/
+
+// AGAIN put the righmost-set-bit concept to use
+// unset the rmost-set-bit ; then XOR the result with the origl number --> only that bit will be set
+
+int rmostsetpos (int x){
+
+ int y = x;
+ int pos = -1; // BCZ I want rmost-bit as pos = 0
+ x &= x-1;
+ y ^= x;
+
+ while(y){
+ y = y >> 1;
+ pos++;
+ }
+ return pos;
+
+}
+
+/*****************************************************************************************************/
+
+
+/******* Uppercase to lowercase, vice-versa, and Toggle***************/
+
+// A is 0100 0001, a is 0110 0001
+// Space character (' ') is 0x20
+// Hence, simply Bitwise-OR A with ' ' to get a
+// And, a to A by Bitwise-AND a with Underscore character('_')
+
+// And to toggle b/n Uppcase and Lowcase, simply XOR with ' '
+
+
+/*****************************************************************************************************/
+
+/******* Count the number of set-bits ***************/
+
+// unset rmost-set-bit until 0 set bits left ?
+
+int countsetbits (int x){
+
+ int count = 0;
+ while (x){
+ x &= x-1; // this unsets the rmost-set-bit
+ count++;
+ }
+ return count;
+}
+
+/*****************************************************************************************************/
+
+/******* Swap endianness using bmpln ***************/
+
+unsigned int swEndn (unsigned int x){ // 0x 1234abcd ---> 0x cdab3412
+
+ x = (x >> 16) | (x << 16); // 0x abcd1234
+ x = ((x & (0xff00ff00)) >> 8) | ((x & (0x00ff00ff)) << 8);
+
+ return x;
+}
+
+/*****************************************************************************************************/
+
+/******* Generate an array with number of set-bits in each index value ***************/
+
+// for any value n, generate an array that is n elements long
+
+void genarr (int n){
+
+ unsigned int arr[n];
+
+ for (int i=0; i<n; i++){
+
+ arr[i] = countsetbits(i);
+ }
+ for (int i=0; i<n; i++){
+
+ printf("%d, ", arr[i]);
+ }
+
+ return;
+}
+
+int main(){
+ 
+ int n = 5;
+ 
+ genarr(n);
+
+ return 0;
+}
+