/*
 * fftmisc.c
 *
 *  Created on: Oct 26, 2015
 *      Author: Hovanes Egiyan
 */

/*============================================================================

 fftmisc.c  -  Don Cross <dcross@intersrv.com>

 http://www.intersrv.com/~dcross/fft.html

 Helper routines for Fast Fourier Transform implementation.
 Contains common code for fft_float() and fft_double().

 See also:
 fourierf.c
 fourierd.c
 ..\include\fourier.h

 Revision history:

 1998 September 19 [Don Cross]
 Improved the efficiency of IsPowerOfTwo().
 Updated coding standards.

 ============================================================================*/

#include <stdlib.h>
#include <stdio.h>
#include <math.h>

#include <fourier.h>

#define TRUE  1
#define FALSE 0

#define BITS_PER_WORD   (sizeof(unsigned) * 8)

unsigned NumberOfBitsNeeded( unsigned PowerOfTwo ) {
	unsigned i;

	if ( PowerOfTwo < 2 ) {
		fprintf( stderr,
				">>> Error in fftmisc.c: argument %d to NumberOfBitsNeeded is too small.\n",
				PowerOfTwo );

		exit( 1 );
	}

	for ( i = 0;; i++ ) {
		if ( PowerOfTwo & (1 << i) ) return i;
	}
	return 0;
}

unsigned ReverseBits( unsigned index, unsigned NumBits ) {
	unsigned i, rev;

	for ( i = rev = 0; i < NumBits; i++ ) {
		rev = (rev << 1) | (index & 1);
		index >>= 1;
	}

	return rev;
}

double Index_to_frequency( unsigned NumSamples, unsigned Index ) {
	if ( Index >= NumSamples )
		return 0.0;
	else if ( Index <= NumSamples / 2 ) return (double) Index / (double) NumSamples;

	return -(double) (NumSamples - Index) / (double) NumSamples;
}

/*--- end of file fftmisc.c---*/