optimization - assembly - x86_64 - predicates -


i coding assembly x86_64 , arm.

i know whether x86_64 has ways define branch predicates.

i searched in intel documentation failed find relevant info.

we have cmov rather slow , cmp jmp combo tends faster.

arm predicates alternative branches. idk mean "branch predicates". maybe mean "predicate conditions"?

cmov worth compared branch skips on 1 or 2 instructions, if it's @ unpredictable. broadwell , skylake run cmov single uop, previous microarchitectures need 2 uops since has 3 input dependencies. creates data dependency instead of control dependency. branch prediction, when works, can better. also, cmov can't take immediate operand, frustrating in many cases.

another instruction can use condition input setcc. use xor reg,reg / set flags / setcc low-byte-of-reg, avoid partial-reg stalls when reading full register.

for carry condition, sbb same,same produce 0 or -1 (useful , mask), or adc reg, 0 reg += cf.


Comments

Post a Comment

Popular posts from this blog

get url and add instance to a model with prefilled foreign key :django admin -

Image
i have page in each contest shown in row. each row contains contest id , link other model names have foreign key contest. news model: class news(models.model): title = models.charfield(max_length=50, null=true) description = models.textfield() time = models.timefield( default= datetime.datetime.now().time()) contest = models.foreignkey(contest) i want use admin adding , changing these models. want when user clicks on 'news' has foreign key contest id=1, shows list of news value foreign key. use {% instance in instances %} <tr class="{% cycle 'row1' 'row2' %}"> <td>{{ instance.title }}</td> <td>{{ instance.starttime }}</td> <td>{{ instance.timespan }}</td> <td>{{ instance.date }}</td> <td><a href="/adm...
Read more

css - Make div keyboard-scrollable in jQuery Mobile? -

from can tell, although jquery-mobile-powered pages can contain divs overflow set scroll or auto, , these divs can scrolled one-screen bar or mouse wheel, cannot scrolled using arrow keys, page-up/page-down, or home/end. instead, official "page" div (with data-role="page") absorbs input. perhaps other divs can't acquire focus, i'm not sure. is there way around this? edit: jsfiddle of simple example: https://jsfiddle.net/qogz0shx/ <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.4/jquery.min.js"></script> <script src="https://ajax.googleapis.com/ajax/libs/jquerymobile/1.4.5/jquery.mobile.min.js"> </script> <link rel="stylesheet" href="https://code.jquery.com/mobile/1.4.5/jquery.mobile-1.4.5.css"/> <style> #outer { overflow:scroll; height: 50vh; width: 50vw; } #inner { height: 500vh; width: 500vw; } ...
Read more

ruby on rails - Seeing duplicate requests handled with Unicorn -

recently upgraded our ec2 instances c3.large in order boost more unicorn workers handle increased traffic our site. (6xworkers per machine - 2 ec2 instances). when did this, started seeing duplicate records being created! looks somehow, maybe 2 unicorn workers attempting process same request? in nginx logs see 1 [post] request particular rails controller - yet 2 records being created in database. i'm hitting kind of race condition issue - have no idea how debug this. doesn't happen time, when it's frustrating well. noticed 2 database records within 5 seconds of each other. (and yes disable button when user clicks submit button). unicorn 4.8.2 ruby 1.9.3 rails 3.2.14 any great! thanks! although may not fix problem, upgrade ruby 2.0.0. there blog mentioning idea upgrade ruby 2.0.0 if using unicorn. for example: https://www.digitalocean.com/community/articles/how-to-optimize-unicorn-workers-in-a-ruby-on-rails-app specifically: if using ruby 1.9, ...
Read more