If you want the fastest way, you will need to use non-portable methods. Windows/MSVC: _BitScanForward() _BitScanReverse() __popcnt() GCC: __builtin_ffs() __builtin_ctz() __builtin_clz() __builtin_popcount() These typically map directly to native hardware instructions. So it doesn’t get much faster than these. But since there’s no C/C++ functionality for them, they’re only accessible via compiler intrinsics.
You cannot! CAST and CONVERT only work to: BINARY[(N)] CHAR[(N)] DATE DATETIME DECIMAL[(M[,D])] SIGNED [INTEGER] TIME UNSIGNED [INTEGER] No room for: BIT, BITINT, TINYINT, MEDIUMINT, BIGINT, SMALLINT, … However, you can create your own function cast_to_bit(n): DELIMITER $$ CREATE FUNCTION cast_to_bit (N INT) RETURNS bit(1) BEGIN RETURN N; END To try it yourself, you can … Read more
Well, the answer is pretty simple. If you have an int value: int log2(int value) { return Integer.SIZE-Integer.numberOfLeadingZeros(value); } The same exists for Long… [Edit] If shaving milliseconds is an issue here, Integer.numberOfLeadingZeros(int) is reasonably efficient, but still does 15 operations… Expanding a reasonable amount of memory (300 bytes, static) you could shave that to … Read more
public byte getBit(int position) { return (ID >> position) & 1; } Right shifting ID by position will make bit #position be in the furthest spot to the right in the number. Combining that with the bitwise AND & with 1 will tell you if the bit is set. position = 2 ID = 5 … Read more
The 8 refers to the number of bytes that the data type uses. So a 32-bit integer is integer*4 along the same lines. A quick search found this guide to Fortran data types, which includes: The “real*4” statement specifies the variable names to be single precision 4-byte real numbers which has 7 digits of accuracy … Read more
Since you mention C as well as C++, I’ll assume that a C++-oriented solution like boost::dynamic_bitset might not be applicable, and talk about a low-level C implementation instead. Note that if something like boost::dynamic_bitset works for you, or there’s a pre-existing C library you can find, then using them can be better than rolling your … Read more
A TINYINT is an 8-bit integer value, a BIT field can store between 1 bit, BIT(1), and 64 bits, BIT(64). For a boolean values, BIT(1) is pretty common.
x ^= x >> 16; x ^= x >> 8; x ^= x >> 4; x ^= x >> 2; x ^= x >> 1; return (~x) & 1; Assuming you know ints are 32 bits. Let’s see how this works. To keep it simple, let’s use an 8 bit integer, for which we can … Read more
An integer is represented as a sequence of bits in memory. For interaction with humans, the computer has to display it as decimal digits, but all the calculations are carried out as binary. 123 in decimal is stored as 1111011 in memory. The & operator is a bitwise “And”. The result is the bits that … Read more
The standard way to do division is by implementing binary long-division. This involves subtraction, so as long as you don’t discount this as not a bit-wise operation, then this is what you should do. (Note that you can of course implement subtraction, very tediously, using bitwise logical operations.) In essence, if you’re doing Q = … Read more