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• Card emulation via software NFC

  - by user85030

  After reading a lot of questions, i decided to post this one. I read that stock version of android does not support API's for card emulation. Also, we cannot write custom applications to secure element embedded in nfc controllers due to keys managed by google/samsung. I need to emulate a card (mifare or desfire etc). The option i can see is doing it via software. I have a ACR122U reader and i've tested that NFC P2P mode works fine with the Nexus-S that i have. 1) I came across a site that said that nexus s's NFC controller (pn532) can emulate a mifare 4k card. If this is true, can i write/read apdu commands to this emulated card? (Probably if i use a modded rom like cyanogenmod) 2) Can i write a android application that reads apdu commands sent from the reader and generate appropriate responses (if not fully, then upto some extent only). To do so, i searched that we need to patch nexus s with cynagenmod. Has someone tried emulating card via this method? I see that this is possible since we have products from access control companies offering mobile applications via which one can open doors e.g. http://www.assaabloy.com/en/com/Products/seos-mobile-access/

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• fastest method for minimum of two numbers

  - by user85030

  I was going through mit's opencourseware related to performance engineering. The quickest method (requiring least number of clock cycles) for finding the minimum of two numbers(say x and y) is stated as: min= y^((x^y) & -(x<y)) The output of the expression x < y can be 0 or 1 (assuming C is being used) which then changes to -0 or -1. I understand that xor can be used to swap two numbers. Questions: 1. How is -0 different from 0 and -1 in terms of binary? 2. How is that result used with the and operator to get the minimum? Thanks in advance.

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