Month: May 2018

Create only root partition during installing OpenBSD

The default partitions of installing OpenBSD is not appropriate for me:
3I need more space for /, since I want to build source code. So I just create one partition:

1 2

Please notice when creating partitions, there are some useful commands. Such as p, which displays current partition status:

4

? is for help:

5

Use z to delete all partitions:

6

Create the root partition and save it:

7 8

Reference:
Easy OpenBSD Partition Scheme.

Install and configure Automake on OpenBSD

Today, when I tried to compile a project, “make” complained following errors:

# make
CDPATH="${ZSH_VERSION+.}:" && cd . && /bin/sh /root/project/missing aclocal-1.15
/root/project/missing[81]: aclocal-1.15: not found
WARNING: 'aclocal-1.15' is missing on your system.
         You should only need it if you modified 'acinclude.m4' or
         'configure.ac' or m4 files included by 'configure.ac'.
         The 'aclocal' program is part of the GNU Automake package:
         <http://www.gnu.org/software/automake>
         It also requires GNU Autoconf, GNU m4 and Perl in order to run:
         <http://www.gnu.org/software/autoconf>
         <http://www.gnu.org/software/m4/>
         <http://www.perl.org/>
*** Error 127 in /root/project(Makefile:330 './aclocal.m4')

To fix it, first install Automake:

# pkg_add automake
quirks-2.414 signed on 2018-03-28T14:24:37Z
Ambiguous: choose package for automake
a       0: <None>
        1: automake-1.10.3p8
        2: automake-1.11.6p2
        3: automake-1.12.6p1
        4: automake-1.13.4p1
        5: automake-1.14.1p0
        6: automake-1.15.1
        7: automake-1.4.6p5
        8: automake-1.8.5p9
        9: automake-1.9.6p12
Your choice: 6
automake-1.15.1:autoconf-2.69p2: ok
automake-1.15.1: ok

Then “make” prompted it needs “AUTOCONF_VERSION“:

# make
CDPATH="${ZSH_VERSION+.}:" && cd . && /bin/sh /root/project/missing aclocal-1.15
Provide an AUTOCONF_VERSION environment variable, please
aclocal-1.15: error: echo failed with exit status: 127
WARNING: 'aclocal-1.15' is missing on your system.
         You should only need it if you modified 'acinclude.m4' or
         'configure.ac' or m4 files included by 'configure.ac'.
         The 'aclocal' program is part of the GNU Automake package:
         <http://www.gnu.org/software/automake>
         It also requires GNU Autoconf, GNU m4 and Perl in order to run:
         <http://www.gnu.org/software/autoconf>
         <http://www.gnu.org/software/m4/>
         <http://www.perl.org/>
*** Error 127 in /root/project/ (Makefile:330 './aclocal.m4')

Set AUTOCONF_VERSION environment variable:

# export AUTOCONF_VERSION=2.69

Run “autoreconf -f -i“:

# autoreconf -f -i
Provide an AUTOMAKE_VERSION environment variable, please
autoreconf-2.69: aclocal failed with exit status: 127

Set AUTOMAKE_VERSION:

# export AUTOMAKE_VERSION=1.15

This time, it worked:

# autoreconf -f -i
# make
/bin/sh ./config.status --recheck
......

The memo of foldl and foldr in Haskell

foldl and foldr are two functions which make people confused easily. Check the types of them:

foldl :: (b -> a -> b) -> b -> [a] -> b 
foldr :: (a -> b -> b) -> b -> [a] -> b

The common characteristic of them is the result type is the same as accumulator: b. A memo to differentiate them is for foldl: it will traverse the elements from the left of list, and the accumulator also works as the left operand of the binary operator: (b -> a -> b). But for foldr, it goes to the opposite side: it will iterate the elements from the right of list, and the accumulator also works as the right operand of the binary operator: (a -> b -> b).

The other important thing is foldr can operate on infinite list whereas foldl not.

 

Serializing binary data in C++

The following is a simple program to serialize data:

#include <fstream>

int main()
{
        int c = 3;
        std::ofstream f("a.txt");
        f << c;

        return 0;
}

Build and run it on Unix OSs (I test on both OpenBSD and Linux):

# c++ test.cc -o test
# ./test
# hexdump -C a.txt
00000000  33                                                |3|
00000001

We can see the integer 3 is saved in text mode, 0x33, which notates ‘3‘ in ASCII. Change the opening file mode to binary:

std::ofstream f("a.txt", std::ios_base::binary);

You will get the same result. So if you want to dump binary data, you may use write function provided by ostream in C++:

# cat test.cc
#include <fstream>

int main()
{
        int c = 3;
        std::ofstream f("a.txt");
        f.write(reinterpret_cast<char*>(&c), sizeof(c));

        return 0;
}
# c++ test.cc -o test
# ./test
# hexdump -C a.txt
00000000  03 00 00 00                                       |....|
00000004

Similarly, istream‘s read can be used to fetch binary data in serialization.

P.S., the full code is here.

Beware NDEBUG controls assert

According to assert document, if NDEBUG is defined, assert actually does nothing:

#ifdef NDEBUG
#define assert(condition) ((void)0)
#else
#define assert(condition) /*implementation defined*/
#endif

So if your program doesn’t trigger assert as you expected, please check whether NDEBUG is defined or not. E.g., if you use cmake to manage the build process, set CMAKE_BUILD_TYPE‘s value as Release will define NDEBUG:

# cmake -DCMAKE_BUILD_TYPE=Release ..
# make VERBOSE=1
......
/opt/cuda/bin/nvcc ...... \"-Wall\",\"-fPIC\",\"-O3\",\"-DNDEBUG\" ......

Warning: don’t put statements in assert, like this:

assert(in >> n);

This will incur the “in >> n” only be executed in debug mode, not release mode.