~ is a bitwise operator that flips all bits in its operand. For example, if your number was 1, its binary representation of the IEEE 754 float (how JavaScript treats numbers) would be… 0011 1111 1111 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 So ~ converts its operand to … 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
Right shift of a negative signed number has implementation-defined behaviour. If your 8 bits are meant to represent a signed 8 bit value (as you’re talking about a “signed 32 bit integer” before switching to 8 bit examples) then you have a negative number. Shifting it right may fill “empty” bits with the original MSB … Read more
How does it work? Our theory was that using such an operator casts the number to an integer, thus removing the fractional part All bitwise operations except unsigned right shift, >>>, work on signed 32-bit integers. So using bitwise operations will convert a float to an integer. Does it have any advantages over doing Math.floor? … Read more
NOTE: All algorithms below are in C, but should be portable to your language of choice (just don’t look at me when they’re not as fast 🙂 Options Low Memory (32-bit int, 32-bit machine)(from here): unsigned int reverse(register unsigned int x) { x = (((x & 0xaaaaaaaa) >> 1) | ((x & 0x55555555) << 1)); … Read more
and tests whether both expressions are logically True while & (when used with True/False values) tests if both are True. In Python, empty built-in objects are typically treated as logically False while non-empty built-ins are logically True. This facilitates the common use case where you want to do something if a list is empty and … Read more
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
See also an earlier version of this answer on another rotate question with some more details about what asm gcc/clang produce for x86. The most compiler-friendly way to express a rotate in C and C++ that avoids any Undefined Behaviour seems to be John Regehr’s implementation. I’ve adapted it to rotate by the width of … Read more
Bitwise operators are operators that work on multi-bit values, but conceptually one bit at a time. AND is 1 only if both of its inputs are 1, otherwise it’s 0. OR is 1 if one or both of its inputs are 1, otherwise it’s 0. XOR is 1 only if exactly one of its inputs … Read more
Two’s complement is a clever way of storing integers so that common math problems are very simple to implement. To understand, you have to think of the numbers in binary. It basically says, for zero, use all 0’s. for positive integers, start counting up, with a maximum of 2(number of bits – 1)-1. for negative … Read more