Notes on computers, programming and all the stuff

Informal specification: __m128i mask_lower(const unsigned n) { assert(n < 16); switch (n) { case 0: return {0x00, ...

Milo Yip has compared different itoa and dtoa implementations on Core i7, including my itoa algorithm 2 , that use SSE2 instructions. R...

Today I had a quite long session with debugger and release code, you know: no debugger symbols and optimized code. I spotted two pieces of a...

SSE provides not widely known control register, called MXCSR . This register plays three roles: controls calculations: flag "flush...

Few years ago I counted instructions from many Linux binaries --- 2014 is good year to repeated this experiment and see that nothing has ch...

I needed to iterate through all values of 32-bit unsigned integer, so I wrote: #include <stdint.h> for (uint32_t i=0; i <= UINT3...

Intel announced new extension to SSE : instructions accelerating calculating hashes SHA-1 and SHA256. As everything else added recently to ...

This instruction is...  FBSTP . The instruction is advanced converter from integer part of floating point number to BCD format. Sounds weird...

Function itoa implemented with SSE instructions is about 3 times faster then scalar CPU version. Read more .

Peter Kankowski compared speed of SSE4.2 instructions crc32 and popcnt against software implementations. Hardware CRC32 is significantly...

With help of BSWAP instruction or SSE instructions ( PSHUFD , PSHUFLW , PSHUFHW ) or SSSE3 instruction ( PSHUFB ) reversing table can be fas...

Method from Bit Twiddling Hacks : (x != 0) && (x & (x-1) == 0) . GCC compiles this to following code: ; input/ouput: eax ; dest...

Suppose we have to exchange (or just move) two registers A and B: C := A xor B C := 0 if condition is not true A := A xor C B := B xor...

Problem: calculate value of sign(x) : -1 when x < 0 0 when x = 0, +1 when x > 0. My solution do not involve any hardware specifi...

This is continuation of subproblem from previous post: we have a word (byte, dword, whatever) and want to fill it with selected bit. 1. Th...

Method presented here allows to get any bit permutation , transposition is just one of possible operations. Lookup-based approach would be f...