=================================================================================== Exercise 2.8-returns the value of the integer x rotated to the right by n positions =================================================================================== Question ======== Write a function rightrot(x,n) that returns the value of the integer x rotated to the right by n positions. .. literalinclude:: cprogs/ex_2.8_rightrot.c :language: c Explanation =========== We need to get the right most bit of the number provided. First we get the right n bits at one time. :: rbit = x << (wordlength() - n); Once we get the right n bits, in order to rotate the value of x, we right shift x for n bits and then OR the result of x with the rbit determined in the previous step. :: x = x >> n; x = x | rbit; For the same example. :: n is between 0 - wordlength() condition 1.when (n == 0) or (n == wordlength()) rightrot(x, 0) == x condition 2. when (n > 0) and (n < wordlength()) like n = 3 x = 0001 1001 the right n bits will be 001. the right rightrot(x,n)result should be 0010 0011 x << (wordlength() - n) = 0001 1001 << (8 - 3) = 0001 1001 << 5 = 0010 0000 So we have got the right most n bits set.Now we right x by 1 and OR the rbit with x. :: x >> n = 0001 1001 >> 3 = 0000 0011 x | rbit = 0000 0011 | 0010 0000 = 0010 0011 Which is our expected result. :: condition 3. when (n > wordlength()) like n = 12 The Compiler will auto transfer "n" to "n % wordlength()", n will be 3, then see "n" as condition 2. The result should be correct too! :: condition 4. when n < 0 (which is not Often use) The result will mirror the function,the rightrot(x,n) function will move the left most n(n > 0)bits to the right side ，the function should called leftrot(x,n). Visualization ============= .. raw:: html