Thread: BIG Problems!!!

Hi again people!!! ...I have gone into a far smaller scope here with my problem, but after hours of messing around have literally got nowhere!!!! here is a small compilable program to show the error!

Code:

/**********************************************************************/
/** file: test.c                                                     **/
/** description: to find out how to stuff two signed short ints into **/
/** an unsigned int and then ustuff them and print the result!       **/
/** author: matt conway.                                             **/
/**********************************************************************/
#include <stdio.h>

unsigned int audioEffect(short int inLeft, short int inRight){

  unsigned int retVal; /* return value */
  short int outLeft, outRight; /* output audio samples */
  
  /* code to process stereo audio data here */
  outLeft = inLeft; /* return input left channel audio data */
  outRight = inRight; /* return input right channel audio data */
  
  /* now return both left and right channel audio data */
  retVal = 0;
  retVal = outLeft << 16; /* stuff left audio data into int */
  retVal |= outRight;
  
  return retVal;

} /* audioEffect() */


int main(void){

  /* example array of audio data for left and right channels */
  short int leftAudio[15]  = {-17,11,59,51,31,42,17,-1,9,-12,-12,20,16,6,27};
  short int rightAudio[15] = {12,78,20,4,-43,5,43,-314,114,-49,-5,113,-98,-32,1};
  
  unsigned int effectedAudio; /* stores result from audioEffect() function */
  short int leftData;  /* result of audio effect for left channel  */
  short int rightData; /* result of audio effect for right channel */
  
  int i; /* loop counter */
  
  printf("example program to show my bitwise problem!\n");

  /* loop through audio data and apply effect */
  for (i=0;i<15;i++){
    
    effectedAudio = 0;
    effectedAudio = audioEffect(leftAudio[i],rightAudio[i]);
    
    /* now extract stereo data */
    leftData  = effectedAudio >> 16;        /* left channel data  */
    rightData = effectedAudio & 0x0000FFFF; /* right channel data */
    
    /* print audio sample before effect and after effect    */
    /* audio effect does nothing, so values should be same! */
    printf("1.Left: %8d, Right: %8d\n", leftAudio[i], rightAudio[i]);
    printf("2.Left: %8d, Right: %8d\n", leftData, rightData);    
    
  } /* loop */
  
  return 0; /* finished */
  
} /* main() */

and for the output...

Code:

example program to show my bitwise problem!
1.Left:      -17, Right:       12
2.Left:      -17, Right:       12
1.Left:       11, Right:       78
2.Left:       11, Right:       78
1.Left:       59, Right:       20
2.Left:       59, Right:       20
1.Left:       51, Right:        4
2.Left:       51, Right:        4
1.Left:       31, Right:      -43
2.Left:       -1, Right:      -43
1.Left:       42, Right:        5
2.Left:       42, Right:        5
1.Left:       17, Right:       43
2.Left:       17, Right:       43
1.Left:       -1, Right:     -314
2.Left:       -1, Right:     -314
1.Left:        9, Right:      114
2.Left:        9, Right:      114
1.Left:      -12, Right:      -49
2.Left:       -1, Right:      -49
1.Left:      -12, Right:       -5
2.Left:       -1, Right:       -5
1.Left:       20, Right:      113
2.Left:       20, Right:      113
1.Left:       16, Right:      -98
2.Left:       -1, Right:      -98
1.Left:        6, Right:      -32
2.Left:       -1, Right:      -32
1.Left:       27, Right:        1
2.Left:       27, Right:        1

Shows that everytime right goes negative, when left is put into the int and then pulled back out it just results to -1 - as pointed out in a previous post earlier today!!!

Thanks again!

your problem - you don't do the explicit convertion

retVal |= outRight;

when outRight is <0 it is extended to the 32 bit with the left bit (becase it is signed value)
so the retVal get not what you wanted...

you should first convert signed short to unsigned short before applying bitwise operations
in this case the expanding to 32-bit value will be done with the 0es