varbyterw.c - fileiopp - File IO ++ or fileiopp serves as a utility that interprets files in ways that I deem useful

varbyterw.c (2260B)
      1 /*
      2   Variable-Byte Reader/Writer implemetation file
      3   varbyterw.c
      4   M. Yamanaka
      5   email: myamanaka@live.com
      6   website: csmyamanaka.com
      7   license: MIT (See included "LICENSE" file for details)
      8 */
      9 
     10 #include "varbyterw.h"
     11 
     12 
     13 int wDataToChar(void* ipt, char* dst, int b, int e){
     14   /*
     15     ipt ... input data
     16     dst ... destination array
     17     b ... number of bytes
     18     e ... endian-ness. 0 indicates little-endian and 1, big-endian
     19   */
     20   
     21   /*
     22     I could be wrong but I'm pretty sure gcc (or at least the version that I'm using) stores variables as little-endian
     23     I came to this conclusion because I tested out the following code:
     24     
     25     int main(){
     26       int n = 65;
     27       int* pn = &n;
     28       char* pcn = (char*)pn;
     29       if(*pcn == '\0' && *(pcn + 3) == 'A') printf("big endian\n");
     30       else if(*pcn == 'A' && *(pcn + 3) == '\0') printf("little endian\n");
     31       else printf("something probably went wrong\n");
     32       return 0;
     33     }
     34 
     35     and got the second print statement.
     36     I don't know if this varies from compiler to compiler.
     37     If it helps, I tested this on Void Linux using GCC 9.3.0
     38   */
     39   
     40   /*
     41     Assuming that the variables are indeed stored in little-endian format,
     42     if match the indices as the bytes are being written,
     43     the resulting byte array should also be little-endian.
     44     If one of the indices is reversed, the result should be big-endian.
     45 
     46     The for-loop below may look a little convoluted but it should handle both cases:
     47     i.e. when e = 0, thereby making (e != 0) = 0, i and j should match
     48     whereas i would count up from 0 to b - 1 and j would count down
     49     from b - 1 to 0 when e = 1 since it would make (e != 0) = 1.
     50     It saves me from having to write two for loops or an if statement in the loop
     51     thereby making the code shorter suckless style
     52   */
     53 
     54   for(int i = 0, j = (b - 1)*(e != 0); i < b; i++, j += 1 - 2*(e != 0)) dst[i] = *((char*)ipt + j);
     55   
     56   return 0;
     57 }
     58 
     59 int rDataFromChar(char* ipt, void* dst, int b, int e){
     60   /*
     61     ipt ... input array
     62     dst ... destination data
     63     b ... number of bytes to interpret
     64     e ... endian-ness, 0 for little-endian and 1 for big-endian
     65   */
     66   
     67   for(int i = 0, j = (b - 1)*(e != 0); i < b; i++, j += 1 - 2*(e != 0)) *((char*)dst + i) = ipt[j];
     68   return 0;
     69 }
     70