main.c


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

/*
Exercise 2-8. Write a function rightrot(x,n)
that returns the value of the
(unsigned) integer x rotated to the right by n bit positions.
*/

unsigned rightrot(unsigned x, int n)
{
#ifndef AMD64
//right rotate assembly instruction is used if the arch is AMD64.
for (int i=0;i<n;++i)
	asm("ror $1, %[x];" : "=r" (x) :[x] "0" (x) );
#else
//slow, but correct.
for (int i=0;i<n;++i)
	{
	/* If the lowest bit is 1, the highest bit needs to be set to 1 to simulate rotating  */
	if (x & 1){x = (x >> 1); x |= (1UL << ((sizeof(x) * CHAR_BIT)-1));}
	/* if the lowest bit is 0, be don't need to rotate */
	else{x = (x >> 1);}
	}
#endif
return x;
}

int main(void)
{
printf("%u\n", rightrot(0xAAA,2147483647));

return 0;
}