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c - Parallelising a function

Tag: c,multithreading,table,rainbowtable

I'm trying to implement parallelism to this function I want it to take as many threads as possible, and write the results to a file.

The results need to be written in the file in the incrementing order so the first result needs to be written first the second second and so on.

The keyGen function is simply an MD5 of the integer m which is used as the start point for each chain. Reduction32 is a reduction function it takes the first 8 byte adds t and returns that value. When a chain reaches its endpoint it is stored in the binary file.

Is there a smart way to make this parallel? without screwing up the order the endpoints are stored in?

void tableGenerator32(uint32_t * text){
    int mMax = 33554432, lMax = 236;
    int m, t, i;
    uint16_t * temp;
    uint16_t * key, ep[2];
    uint32_t tp;
    FILE * write_ptr;
    write_ptr = fopen("table32bits.bin", "wb");
    for(m = 0; m < mMax ; m++){
        key = keyGen(m);
        for (t = 0; t < lMax; t++){
            keyschedule(key);
            temp = kasumi_enc(text);
            tp = reduction32(t,temp);
            temp[0]=tp>>16;
            temp[1]=tp;
            for(i=0; i < 8; i++){
                key[i]=temp[i%2];
            }
        }
        for(i=0;i<2;i++)
            ep[i] = key[i];

        fwrite(ep,sizeof(ep),1,write_ptr);
    }
    fclose(write_ptr);
}

Best How To :

The best way to parallelize the above function without facing concurrency issues is to create as many memory streams as many threads you wish to use and then divide the task into fractions, like if you have 4 threads,

  • one thread performs the task from 0 to mMax / 4
  • one thread performs the task from mMax / 4 to (mMax / 4) * 2
  • one thread performs the task from (mMax / 4) * 2 to (mMax / 4) * 3
  • one thread performs the task from (mMax / 4) * 3 to (mMax / 4) * 4

then you concatenate the result streams and write them into a file.

wait for an event regulary

multithreading,events

I solve it I use threading and producer/consumer problem. after an event it will wait until event method run.

Images not appearing on WPF form when loading asynchronously

c#,wpf,multithreading,listbox,backgroundworker

@Clemens answer from his comment on the original question provided the solution. Ensuring that the file stream was being closed responsibly and changing the BitmapCacheOption to OnLoad now shows each image in the asynchronous load. The final code for the asynchronous load looks like: private void LoadAsync(object sender, DoWorkEventArgs e)...

How to increment the value of an unsigned char * (C)

c++,c,openssl,byte,sha1

I am assuming your pointer refers to 20 bytes, for the 160 bit value. (An alternative may be text characters representing hex values for the same 160 bit meaning, but occupying more characters) You can declare a class for the data, and implement a method to increment the low order...

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java,multithreading,wait

have a a look at the classes in java.util.conucurrent ... CountDownLatch might be a solution for your problem if i understand your problem correctly.

Program to reverse a string in C without declaring a char[]

c,string,pointers,char

Important: scanf(" %s", name); has no bounds checking on the input. If someone enters more than 255 characters into your program, it may give undefined behaviour. Now, you have the char array you have the count (number of char in the array), why do you need to bother doing stuffs...

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c++,c,nm

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getchar() not working in c

c,while-loop,char,scanf,getchar

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c,arrays,segmentation-fault,initialization,int

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c,char,segmentation-fault,user-input,scanf

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c,binary-tree,binary-search-tree

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c,prng,shift-register

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c,visual-studio-2012,linker,static-libraries

C++ uses something called name mangling when it creates symbol names. It's needed because the symbol names must contain the complete function signature. When you use extern "C" the names will not be mangled, and can be used from other programming languages, like C. You clearly make the shunt library...

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c,printf,format-string

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CallXXXMethod undefined using JNI in C

java,c,jni

There are few fixes required in the code: CallIntMethod should be (*env)->CallIntMethod class Test should be public Invocation should be jint age = (*env)->CallIntMethod(env, mod_obj, mid, NULL); Note that you need class name to call a static function but an object to call a method. (cls2 -> person) mid =...

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c,embedded,stm32,gnu-arm,coocox

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c,armcc,predefined-macro

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ios,objective-c,multithreading,swift,grand-central-dispatch

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java multithreading start() and run() [duplicate]

java,multithreading

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c,arrays,pebble-watch,cloudpebble

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vb.net,multithreading,winforms

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c#,multithreading,performance,loops

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c,format,sscanf,c-strings

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c,opengl

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c,macros

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c,exec,ipc

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c,go,xlib,cgo

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c,c89,post-increment,ansi-c

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java,multithreading,locking

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c,arrays,loops,malloc,fread

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linux,multithreading,linux-kernel

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c,execl

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c,pointers,dynamic-memory-allocation,behavior,realloc

Yes, ptr2 is unaffected by realloc(), it has no connection to realloc() call whatsoever(as per the current code). However, FWIW, as per the man page of realloc(), (emphasis mine) The realloc() function returns a pointer to the newly allocated memory, which is suitably aligned for any kind of variable and...

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c,scope

The only difference between the two is the scope of the else. Without the braces, it spans until the end of the full statement, which is the next ;, i.e the next line: else putchar(ch); /* end of else */ lastch = ch; /* outside of if-else */ With the...

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c,vector,struct

What is happening is that tPeca pecaJogo[tam]; is a local variable, and as such the whole array is allocated in the stack frame of the function, which means that it will be deallocated along with the stack frame where the function it self is loaded. The reason it's working is...

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c++,c,macros

Are DETUNE1 and DETUNE2 calculated every time it is called? Very unlikely. Because you are calling sqrt with constants, most compilers would optimize the call to the sqrt functions and replace it with a constant value. GCC does that at -O1. So does clang. (See live). In the general...

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c++,multithreading

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c,function,serial-port,posix

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c,memory-management,out-of-memory,realloc

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c,function,recursion,comma

In your first code, Case 1: return reverse(i++); will cause stack overflow as the value of unchanged i will be used as the function argument (as the effect of post increment will be sequenced after the function call), and then i will be increased. So, it is basically calling the...

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c,openssl,cryptography,rsa

pub_l = malloc(sizeof(pub_l)); is simply not needed. Nor is priv_l = malloc(sizeof(priv_l));. Remove them both from your function. You should be populating your out-parameters; instead you're throwing out the caller's provided addresses to populate and (a) populating your own, then (b) leaking the memory you just allocated. The result is...

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c,strlen

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java,multithreading,synchronization

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c,if-statement,macros,logic

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mysql,c

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c,algorithm,security,math,encryption

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c,strcpy

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java,multithreading

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free causing different results from malloc

c,string,malloc,free

Every time you are creating your string, you are not appending a null terminator, which causes the error. So change this: for(j=0; j<rem_len; j++) { if(j != i) { remaining_for_next[index_4_next] = remaining[j]; index_4_next++; } } to this: for(j=0; j<rem_len; j++) { if(j != i) { remaining_for_next[index_4_next] = remaining[j]; index_4_next++; }...

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c,text,alignment

From printf's manual: The field width An optional decimal digit string (with nonzero first digit) specifying a minimum field width. If the converted value has fewer characters than the field width, it will be padded with spaces on the left (or right, if the left-adjustment flag has been given). Instead...

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c#,multithreading,file-search

Instead of using ordinary foreach statement in doing your search, you should use parallel linq. Parallel linq combines the simplicity and readability of LINQ syntax with the power of parallel programming. Just like code that targets the Task Parallel Library. This will shield you from low level thread manipulation and...