;Example 3 - 24. Generation Index Tab C Listing for a Bit Reversion Function
/*============================================================= */
/* TEXAS INSTRUMENTS, INC. */
/* NAME: bitrev_index */
/* USAGE */
/* This function has the prototype: */
/* void bitrev_index(short *index, int n); */
/* index[sqrt(n)] : Pointer to index table that is */
/* returned by the routine. */
/* n: Number of complex array elements to bit-reverse. */
/* DESCRIPTION */
/* This routine calculates the index table for performing a */
/* complex bit reversal of an array of length n. The length */
/* of the index table is 2^(2*ceil(k/2)) where n = 2^k. In */
/* other words, the length of the index tab is sqrt(n) for */
/* even powers of radix. */
/*============================================================= */
void bitrev_index(short *index, int n)
{
int i, j, k, radix = 2;
short nbits, nbot, ntop, ndiff, n2, raddiv2;
nbits = 0; i = n;
while (i > 1){
i = i >> 1; nbits++;
}
raddiv2 = radix >> 1;
nbot = nbits >> raddiv2;
nbot = nbot ndiff = nbits & raddiv2;
ntop = nbot + ndiff;
n2 = 1
index[0] = 0;
for ( i = 1, j = n2/radix + 1; i < n2 - 1; i++){
index[i] = j - 1;
for (k = n2/radix; k*(radix-1) < j; k /= radix)
j -= k*(radix-1);
j += k;
}
index[n2 - 1] = n2 - 1;
}
