Using Shift Operators in C
By: Fazal in C Tutorials on 2007-10-03
Two shift operators shift the bits in an integer variable by a specified number of positions. The << operator shifts bits to the left, and the >> operator shifts bits to the right. The syntax for these binary operators is
x << n
and
x >> n
Each operator shifts the bits in x by n positions in the specified direction. For a right shift, zeros are placed in the n high-order bits of the variable; for a left shift, zeros are placed in the n low-order bits of the variable. Here are a few examples:
Binary 00001100 (decimal 12) right-shifted by 2 evaluates to binary 00000011 (decimal 3).
Binary 00001100 (decimal 12) left-shifted by 3 evaluates to binary 01100000 (decimal 96).
Binary 00001100 (decimal 12) right-shifted by 3 evaluates to binary 00000001 (decimal 1).
Binary 00110000 (decimal 48) left-shifted by 3 evaluates to binary 10000000 (decimal 128).
Under certain circumstances, the shift operators can be used to multiply and divide an integer variable by a power of 2. Left-shifting an integer by n places has the same effect as multiplying it by 2n, and right-shifting an integer has the same effect as dividing it by 2n. The results of a left-shift multiplication are accurate only if there is no overflow--that is, if no bits are "lost" by being shifted out of the high-order positions. A right-shift division is an integer division, in which any fractional part of the result is lost. For example, if you right-shift the value 5 (binary 00000101) by one place, intending to divide by 2, the result is 2 (binary 00000010) instead of the correct 2.5, because the fractional part (the .5) is lost. Sample program demonstrates the shift operators.
Using the shift operators.
1: /* Demonstrating the shift operators. */ 2: 3: #include <stdio.h> 4: 5: main() 6: { 7: unsigned int y, x = 255; 8: int count; 9: 10: printf("Decimal\t\tshift left by\tresult\n"); 11: 12: for (count = 1; count < 8; count++) 13: { 14: y = x << count; 15: printf("%d\t\t%d\t\t%d\n", x, count, y); 16: } 17: printf("\n\nDecimal\t\tshift right by\tresult\n"); 18: 19: for (count = 1; count < 8; count++) 20: { 21: y = x >> count; 22: printf("%d\t\t%d\t\t%d\n", x, count, y); 23: } 24: return(0); 25: } Decimal shift left by result 255 1 254 255 2 252 255 3 248 255 4 240 255 5 224 255 6 192 255 7 128 Decimal shift right by result 255 1 127 255 2 63 255 3 31 255 4 15 255 5 7 255 6 3 255 7 1
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