Wojciech Muła --- website

Suppose we need to get a mask when a nonnegative argument is greater then some constant value; in other words, we want to evaluate following expression: if x > const_n then mask := 0xffffffff; else mask := 0x00000000; Portable branchless solution:…

Tests Two scenarios of test were considered: The table size is hardware friendly, i.e. is multiply of implementation base step; also address of table is aligned: all procedures use MOVUPS, all procedures use MOVAPS.

Method from Bit Twiddling Hacks: (x !

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 C If C is 0, then A and B left unchanged, else A and B are swapped.

The idea is quite simple: we do not have a single stl::map<string, something>, but a vector of maps, indexed with O(1) time — each map stores keys sharing certain properties.

Problem: calculate value of sign(x): -1 when x < 0 0 when x = 0, +1 when x > 0.

The most general algorithm mask bit: [10111010] => [00010000] clone word: a=[00010000], b=[00010000] shift bit in first word to MSB, and to LSB in second word: a=[10000000], b=[00000001] subtract c = a - b: c=[01111111] add missing MSB c = c OR a: c=[…

Method presented here allows to get any bit permutation, transposition is just one of possible operations.

Suppose that a database stores some kind of a dictionary and an user picks some items, but wants to keep the order.

man locatedb says: "Databases can not be concatenated together, even if the first (dummy) entry is trimmed from all but the first database.

Unusual application of PHMINPOSUW instruction as key part of insertion sort for 8 element tables.

Introduction Image crossfading is a kind of alpha blending where a final pixel is the result of linear interpolation of pixels from two images: result_pixel = pixel1 * alpha + pixel2 * (1 - alpha) where alpha lie in range [0, 1].

There is no such instruction — CVTDQ2PS converts signed 32-bit ints.

Converting float to int Few years ago I've developed a method that do not need any floating-point operations — description is written in Polish, but sample code should be easy to understand.

Branch-less x86 code: movl %eax, %ebx sarl $32, %ebx ; fill ebx with sign bit xorl %ebx, %eax ; negate eax (if negative) subl %ebx, %eax ; increment eax by 1 (if negative) SSE2: pshufd $0b11110101, %xmm0, %xmm1 ; populate…

RDTSC is incremented with bus-clock cycles, and then multiplied by core-clock/bus-clock ratio.

Read-write variables asm( "

Introduction Alpha blending refers to many different operations.

Proof In the proof we consider three cases: x < y, x = y and x > y.

x86 code The x86 code is a base for further improvements.

Introduction Basically this kind of conversion needs following steps: extract components R, G and B (using bitwise and) extend words from 6 or 5 bits to 8 bits (shift left) place components at desired places in a 32-bit word (shift, bitwise or) R = (pixel…

Introduction String search is a common task in text processing.

Introduction Population count is a procedure of counting number of ones in a bit string.

SIMD algorithm Instruction PSHUFB does parallel lookup from 16-byte array stored in an XMM register — this is exactly what bin to hex conversion needs.