java is faster then c (2015)

java is faster then c

1) Heap alloc vs stack alloc
not a problem.
optimized?

2) New object in loop
not a problem.
reuse, optimized?

3) memory copy
not a problem
substring, byte array,
case by case, write good java source.

4) boundary check
java faster then c even with additional boundary check.

5) jdk size and startup time
wait java 9 with modular!

6) for loop in java vs memcmp, memcpy in c
not a problem
like a magic

How to Install Windows 7, the hack way

How to Install Windows 7, the hack way
========================================================

# The normal way

 * use a usb-stick or CD-ROM installer
 * install win7
 * apply patches using windows updates

However, it costs hours, it's so clumsy that win7 do not apply patches in one time,
but download and install and reboot for serveral times.

Also some device drivers need to be installed manually.


# The easy way to dupliate a win7 installation.

 * copy windows system partition into a new partition(on same disk or new disk).
 * fix it (describe later)
 * done

## details
 * Scene 1 , the old disk is going to break, you need to move windows system into a new disk (maybe faster SSD)
 * Scene 2 , you need a new windows 7 system for the new machine.

 Step 1, copy the whole windows system partition(call it "System partition" later) to new target
 ```
     I do it in linux,
     cp -rp Win7Partition NewWin7Partition
 ```

 Step 2, you need a bootable windows partition(call it "bootmgr" later)
  * windows 7 use a 100MB partition as "bootmgr",
  * the size can be larger or smaller
  * actually it can be on the same partition as "System partition",
  * "System partition" can be on an extended partition, but "Bootmgr" must be on the primary partition(because win7's foolish).
  I'm talking about the traditional partition table, the are only 4 slot,
  alloc it as 4 primary
  or 3 primary + 1 extended (which contains infinity number of partition in theory but actually OS/bootloader will panic when you alloc too many)
  * the partition "bootmgr" on, need tagged as "active", do it use fdisk (command a , toggle as bootable) or other tools like diskpart(on win7 installer disk)
  * "bootmgr" need a bootloader program called bootmgr, which is a hidden file in root directory.
    it can be created by `bootsect /nt60 all /force` (or maybe just copy the file)
    it is safe to execute the command because it only affect dos/ntfs partition, your linux ext4 partition will stay safe, and
    it is about to copy file, and will not write to MBR actually, unless you add "/mbr" option.
  * bootmgr install need a BCD config, stored in BCD folder on the same partition of bootmgr file.
  which can be installed by 'bcdboot x: /s y:', you can delete old BCD folder, so that the command can create a new "correct" one for you.
  * the BCD can be viewed using `bcdedit /store file /enum /v` or be edited if necessary.
  * BCD is same role as grub.cfg file in GRUB, it can load multipy windows on different locations, but it cannot load linux I guess.

## Conclusion
  the keys are (1)A primary partition flagged as "active", (2) "bootmgr" single file on the primary partition,
  (3) BCD directory with correct config on the same partition of "bootmgr"

  In the end, you need a working bootloader, the true bootloader which installed physically on the the first sector of the disk.
  which can be a windows one, or GRUB2(linux way), using "chainloader +1"

The process is:
  * BIOS of motherboard load bootloader from first sector of disk
  * bootloader loads itself then bootmgr
  * bootmgr check active flag
  * bootmgr load BCD config
  * bootmgr load \windows\winload.exe(on which partition is according to UUID in BCD config file) to start windows.


If you get more troubles, try using the follow tools:
 * bootsect
 * bootrec
 * bcdboot
 * bcdedit

you may also need
 * grub-install
 * update-grub
If you also use Linux.

intercepted 550 User not found;

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Use single regular file as a filesystem

Why? it can be for portable,virtual,develop,audit,test,free,... nice things.

make a empty regular file
    dd if=/dev/zero of=myExt4.img bs=4K count=1000

check if loop device available on your system:
    ls /dev/loop*

if there is no loop device, need to load kernel modules, or even compile loop module:

    (Linux 3.16.1)
    make menuconfig
    Device Drivers -> Block Devices -> Loopback device support
    make -j4
    make modules_install
   
    modprobe loop
    ls /dev/loop*

use loop device

    losetup /dev/loop0 myExt4.img
    mkfs.ext4 /dev/loop0
    mount /dev/loop0 /mnt   
    echo "world">/mnt/hello
    df
    umount /mnt

done.



ADD:
use modprobe loop max_part=31
and fdisk /dev/loop0
mkfs /dev/loop0p1
to work on virtual multi-partition disk.

Load your OS kernel by Grub2 in a single file.

BIOS loads MBR in 512 bytes into memory 0000h:7c00h

But grub2 can load a whole file into memory 0000h:7c00h,(with a patch)
that means you can write your hobbist OS in one single file.
In this way, maybe other existing OS can be loaded easily.

in grub1 there is command "kernel=file" but I cannot find it in grub2.
grub2 has command linux16, but has other restriction about the format.
grub2 also provides command multiboot, but also spec condition should be met.

The method mentioned here, need only one condition is, the last 2 bytes of first 512 bytes
should be hex 55AA.

and the kernel file could be put in any existing filesystem can be recognized by grub2.

eg:
menuentry 'NEOS on vfat' {
    insmod chain
    insmod fat
    set root='hd0,msdos4'
    chainloader /neoskern
}
or:
menuentry 'NEOS on ext4' {
    insmod part_msdos
    insmod chain
    insmod ext2
   
    set root='hd0,msdos7'
    chainloader /boot/neoskern
}

the patch info is here: http://savannah.gnu.org/bugs/?43184

8192cu on linux 3.16.1

It is said that 8192cu wifi driver is buggy.
I download driver from the maker site RTL8188C_8192C_USB_linux_v4.0.2_9000.20130911
cannot compile because /proc API is changed since 3.10
I found patched versions on the net, they just make the /proc part dummy.
and I see interface wlan1(or wlan0 on yours). but no wireless extension using iwconfig. and Unsupported driver 'nl80211'. and ioctl[SIOCSIWMODE]: Operation not supported if use -DWext. 
At last I found kernel modules for it is just not compiled(I used self-compiled kernel). And I tried default rtl8192cu module of kernel.
It worked.

I just don't know the reason.
But I learned to try kernel drivers.

install wifi usb driver ralink 7601 (FAILED)

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