If you want the k-th bit of n, then do (n & ( 1 << k )) >> k Here we create a mask, apply the mask to n, and then right shift the masked value to get just the bit we want. We could write it out more fully as: int mask = 1 … Read more
Because nextDouble works like this: (source) public double nextDouble() { return (((long) next(26) << 27) + next(27)) / (double) (1L << 53); } next(x) makes x random bits. Now why does this matter? Because about half the numbers generated by the first part (before the division) are less than 1L << 52, and therefore their … Read more
Bit Twiddling Hacks offers an excellent collection of, er, bit twiddling hacks, with performance/optimisation discussion attached. My favourite solution for your problem (from that site) is «multiply and lookup»: unsigned int v; // find the number of trailing zeros in 32-bit v int r; // result goes here static const int MultiplyDeBruijnBitPosition[32] = { 0, … Read more
This should work: unsigned char reverse(unsigned char b) { b = (b & 0xF0) >> 4 | (b & 0x0F) << 4; b = (b & 0xCC) >> 2 | (b & 0x33) << 2; b = (b & 0xAA) >> 1 | (b & 0x55) << 1; return b; } First the left four … Read more
Let’s take a look at ASCII code table in binary. A 1000001 a 1100001 B 1000010 b 1100010 C 1000011 c 1100011 … Z 1011010 z 1111010 And 32 is 0100000 which is the only difference between lowercase and uppercase letters. So toggling that bit toggles the case of a letter.
GCC has: — Built-in Function: int __builtin_clz (unsigned int x) Returns the number of leading 0-bits in X, starting at the most significant bit position. If X is 0, the result is undefined. — Built-in Function: int __builtin_clzl (unsigned long) Similar to `__builtin_clz’, except the argument type is `unsigned long’. — Built-in Function: int __builtin_clzll … Read more
Assume for the sake of contradiction that there exists some x and some y (mod 2n) such that ~(x+y) == ~x + ~y By two’s complement*, we know that, -x == ~x + 1 <==> -1 == ~x + x Noting this result, we have, ~(x+y) == ~x + ~y <==> ~(x+y) + (x+y) == … Read more
When shifting left, there is no difference between arithmetic and logical shift. When shifting right, the type of shift depends on the type of the value being shifted. (As background for those readers unfamiliar with the difference, a “logical” right shift by 1 bit shifts all the bits to the right and fills in the … Read more
Short Answer You want to do an Bitwise AND operation on the current value with a Bitwise NOT operation of the flag you want to unset. A Bitwise NOT inverts every bit (i.e. 0 => 1, 1 => 0). flags = flags & ~MASK; or flags &= ~MASK;. Long Answer ENABLE_WALK = 0 // 00000000 … Read more
xor is a dangerous default function to use when hashing. It is better than and and or, but that doesn’t say much. xor is symmetric, so the order of the elements is lost. So “bad” will hash combine the same as “dab”. xor maps pairwise identical values to zero, and you should avoid mapping “common” … Read more