Klaus Post klauspost

Count Leading/Trailing Zero Bits (Byte-wise)

Counting the trailing zero bit count (TZCNT) can be done by isolating the lowest bit, then depositing this into the appropriate locations for the count. The leading zero bit count (LZCNT) can be done by reversing bits, then computing the TZCNT.

__m128i _mm_tzcnt_epi8(__m128i a) {
	// isolate lowest bit
	a = _mm_andnot_si128(_mm_add_epi8(a, _mm_set1_epi8(0xff)), a);
	// convert lowest bit to index

Google Drive File Picker Example

This is an example of how to use the Google Drive file picker and Google Drive API to retrieve files from Google Drive using pure JavaScript. At the time of writing (14th July 2013), Google have good examples for using these two APIs separately, but no documentation on using them together.

Note that this is just sample code, designed to be concise to demonstrate the API. In a production environment, you should include more error handling.

See a demo at http://stuff.dan.cx/js/filepicker/google/

	#include <stdio.h>
	#include <x86intrin.h>
	#include <stdint.h>
	#include <stdlib.h>
	#include <string.h>

	int main(void) {
	__m128i polymask1 = _mm_set1_epi64x(0xff00ffffff000000ULL); // polynomial 0x11d: 0x1d = 0b11101, reverse bits -> 10111000, then replace 1->ff, 0->00

	for(int val=0; val<256; val++) {

	#include <stdint.h>

	typedef unsigned char U8;
	typedef unsigned short U16;
	typedef unsigned int U32;
	typedef unsigned long long U64;
	typedef intptr_t SINTa;

	struct KernelState
	{

	; NOTE: all just a quick sketch
	; also I'm using xmm/ymm/zmm0-5 and then 16-31
	; because Win64 ABI expects me to preserve ymm6-ymm15
	; and I couldn't be bothered to set up a stack frame and save them :)
	;
	; Meant to be assembled with NASM

	section .data

	vone dd 1