[Complexity] Optimize minimum_s()

Basic info

This is a subtask of #1009 (closed) - it splits off the complexity optimization of the function minimum_s(). This optimization is BE.

Bug description

The proposed patch removes the IF() condition in the FOR-loop and replaces it by an if(). The minimum value is not stored, just the array index, which allows for this optimization.

Word16 minimum_s(
    const Word16 *vec, /* i  : Input vector                      */
    const Word16 lvec, /* i  : Vector length                     */
    Word16 *min_val    /* o  : minimum value in the input vector */
)
{
#ifdef PATCH
    Word16 i, ind;
#else
    Word16 i, ind, tmp;
#endif

    ind = 0;
    move16();
#ifndef PATCH
    tmp = vec[0];
    move16();
#endif

    FOR( i = 1; i < lvec; i++ )
    {
#ifdef PATCH
        if ( LT_16( vec[i], vec[ind] ) )
        {
            ind = add( i, 0 );
        }
#else
        IF( LT_16( vec[i], tmp ) )
        {
            ind = i;
            move16();
            tmp = vec[i];
            move16();
        }
#endif
    }

    if ( min_val != NULL )
    {
#ifdef PATCH
        *min_val = vec[ind];
#else
        *min_val = tmp;
#endif
        move16();
    }

    return ind;
}

The proposed patch saves 4 cycles per FOR iteration.

Ways to reproduce

(Clear steps or refer to a failing automated test, e.g. with a pipeline link)