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From: fir <fir@grunge.pl>
Newsgroups: comp.lang.c
Subject: Re: macro for fir list?
Date: Sat, 30 Mar 2024 14:13:04 +0100
Organization: i2pn2 (i2pn.org)
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fir wrote:
> bart wrote:
>> On 30/03/2024 09:56, fir wrote:
>>
>>>>
>>> yet other example
>>>
>>> //bytes container
>>>    char* bytes = NULL; int bytes_size = 0;
>>>    void bytes_add(char val) {
>>> (bytes=(char*)realloc(bytes,++bytes_size*sizeof(char)))[bytes_size-1]=val;
>>>
>>>  }
>>>    void bytes_load(char* name)  {    FILE *f = fopen(name, "rb"); int
>>> c; while((c=getc(f))!=EOF) bytes_add(c);   fclose(f);  }
>>
>> This is pretty inefficient. Loading an 8MB file this way takes 3
>> seconds, vs. 50ms to load it in one go.
>>
>> Loading the same 90KB file 10,000 times took 120 seconds, vs. 0.8
>> seconds even using a scripting language.
>>
>> 80% of the inefficiency is growing the buffer one byte at a time. The
>> other 20% is reading the file one byte at a time.
>>
>>
> i know its inneficient but that was not the point - the point was  more
> about composition and utility
>
> i may revrite but the example would be much longer
>
>    char* bytes = NULL; int bytes_size = 0;
>    char* bytes_resize(char size) {return
> bytes=(char*)realloc(bytes,(bytes_size=size)*sizeof(char));  }
>    void bytes_add(char val) {
> (bytes=(char*)realloc(bytes,++bytes_size*sizeof(char)))[bytes_size-1]=val;
>   }
>    void bytes_save(char* name)  {    FILE* f =fopen(name, "wb"); int
> saved = fwrite (bytes , 1, bytes_size, f); fclose (f);  }
>
>
>   int GetFileSize2(char *filename)
>   {
>      struct stat st;
>      if (stat(filename, &st)==0) return (int) st.st_size;
> //    ERROR_EXIT("error obtaining file size for &s", filename);
>      return -1;
>   }
>
>    void bytes_load(char* name)
>    {
>      int flen = GetFileSize2(name);
>      FILE *f = fopen(name, "rb");
>      int loaded = fread(bytes_resize(flen), 1, flen, f);
>      fclose(f);
>     }
>
> generally if some uses this bytes microcintainer (i call it also list,
> though it is also resizable array) one may use thie add method which
> callst reallock or call resize(1000) and use it by bytes[i] so its not
> inefficient
>
> //@include "bytes.c"
> for(int i=0;i<1000;i++) bytes_add(rand()&0xff);
>
> bytes_resize(1000);
> for(int i=0;i<1000;i++) bytes[i]=rand()&0xff;
>

yoy may check how much it last to say insert 1M of bytes by add compared 
to resize and put it normall way - thic could measure overhead of this 
reallock... i may add this variable say _cached_size or what to name it, 
its a line of code ot wo and that will speed up but there still be a 
cost of if