Because in 2’s complement, -n is ~n+1. If n is a power of 2, then it only has one bit set. So ~n has all the bits set except that one. Add 1, and you set the special bit again, ensuring that n & (that thing) is equal to n. The converse is also true … Read more
Solution: static _Bool IsCompact(unsigned x) { return (x & x + (x & -x)) == 0; } Briefly: x & -x gives the lowest bit set in x (or zero if x is zero). x + (x & -x) converts the lowest string of consecutive 1s to a single 1 higher up (or wraps to … Read more
You are exactly right. It’s an artifact of two’s complement integer representation. In 16 bits, 1 is represented as 0000 0000 0000 0001. Inverted, you get 1111 1111 1111 1110, which is -2. Similarly, 15 is 0000 0000 0000 1111. Inverted, you get 1111 1111 1111 0000, which is -16. In general, ~n = -n … Read more
The article Branchfree Saturating Arithmetic provides strategies for this: Their addition solution is as follows: u32b sat_addu32b(u32b x, u32b y) { u32b res = x + y; res |= -(res < x); return res; } modified for uint8_t: uint8_t sat_addu8b(uint8_t x, uint8_t y) { uint8_t res = x + y; res |= -(res < x); … Read more
Use the bitwise OR (|) and AND (&) operators. To set a bit, namely turn the bit at pos to 1: my_byte = my_byte | (1 << pos); // longer version, or my_byte |= 1 << pos; // shorthand To un-set a bit, or turn it to 0: my_byte = my_byte & ~(1 << pos); … Read more
Yes, the ~ operator will work. update foo set Sync = ~@IsNew
Two’s complement subtracts off (1<<bits) if the highest bit is 1. Taking 8 bits for example, this gives a range of 127 to -128. A function for two’s complement of an int… def twos_comp(val, bits): “””compute the 2’s complement of int value val””” if (val & (1 << (bits – 1))) != 0: # if … Read more
1. Detecting the overflow: x = a * b; if (a != 0 && x / a != b) { // overflow handling } Edit: Fixed division by 0 (thanks Mark!) 2. Computing the carry is quite involved. One approach is to split both operands into half-words, then apply long multiplication to the half-words: uint64_t … Read more
Check out the Color class. Your code would look a bit something like this. int color = 0xFFFFFFFF; int transparent = Color.argb(0, Color.red(color), Color.green(color), Color.blue(color)); So wrapping it in a method might look like: @ColorInt public static int adjustAlpha(@ColorInt int color, float factor) { int alpha = Math.round(Color.alpha(color) * factor); int red = Color.red(color); int … Read more
You are actually doing this: var_dump(0b10 & (0b01 == 0)); var_dump(0b10 & (0b01 != 0)); Try: var_dump((0b10 & 0b01) == 0); var_dump((0b10 & 0b01) != 0);