Math.addExact throws exception on overflow Since Java 8 there is a set of methods in the Math class: toIntExact(long) addExact(int,int) subtractExact(int,int) multiplyExact(int,int) …and versions for long as well. Each of these methods throws ArithmeticException if overflow happens. Otherwise they return the proper result if it fits within the range. Example of addition: int x = … Read more
Both GCC and clang generate beautiful assembly for the following simple, straightforward, portable code: double clamp(double d, double min, double max) { const double t = d < min ? min : d; return t > max ? max : t; } > gcc -O3 -march=native -Wall -Wextra -Wc++-compat -S -fverbose-asm clamp_ternary_operator.c GCC-generated assembly: maxsd … Read more
This can be done using SSE2 as follows: void ExpandSSE2(unsigned __int64 in, unsigned __int64 &outLo, unsigned __int64 &outHi) { __m128i const mask = _mm_set1_epi16((short)0xF00F); __m128i const mul0 = _mm_set1_epi16(0x0011); __m128i const mul1 = _mm_set1_epi16(0x1000); __m128i v; v = _mm_cvtsi64_si128(in); // Move the 64-bit value to a 128-bit register v = _mm_unpacklo_epi8(v, v); // 0x12 -> … Read more
He meant that taking number mod 2^n is equivalent to stripping off all but the n lowest-order (right-most) bits of number. For example, if n == 2, number number mod 4 00000001 00000001 00000010 00000010 00000011 00000011 00000100 00000000 00000101 00000001 00000110 00000010 00000111 00000011 00001000 00000000 00001001 00000001 etc. So in other words, number … Read more
Numbers can be expressed in binary like this: 3 = 000011 5 = 000101 10 = 001010 …etc. I’m going to assume you’re familiar with binary. Bitwise AND means to take two numbers, line them up on top of each other, and create a new number that has a 1 where both numbers have a … Read more
Bitfields are not quite as portable as you think, as “C gives no guarantee of the ordering of fields within machine words” (The C book) Ignoring that, used correctly, either method is safe. Both methods also allow symbolic access to integral variables. You can argue that the bitfield method is easier to write, but it … Read more
the recursive solution to towers of Hanoi works so that if you want to move N disks from peg A to C, you first move N-1 from A to B, then you move the bottom one to C, and then you move again N-1 disks from B to C. In essence, hanoi(from, to, spare, N): … Read more
To check to see if a bit value is set: int value = VALUE_TO_CHECK | OTHER_VALUE_TO_CHECK; if ((value & VALUE_TO_CHECK) == VALUE_TO_CHECK) { // do something–it was set } if ((value & OTHER_VALUE_TO_CHECK) == OTHER_VALUE_TO_CHECK) { // also set (if it gets in here, then it was defined in // value, but it does not … Read more
document.write( (1 << 31) +”<br/>”); The << operator is defined as working on signed 32-bit integers (converted from the native Number storage of double-precision float). So 1<<31 must result in a negative number. The only JavaScript operator that works using unsigned 32-bit integers is >>>. You can exploit this to convert a signed-integer-in-Number you’ve been … Read more
The typical way is to shift and subtract. This is basically pretty similar to long division as we learned it in school. The big difference is that in decimal division you need to estimate the next digit of the result. In binary, that’s trivial. The next digit is always either 0 or 1. If the … Read more