www.pudn.com > fftjd.rar > FFTMISC.C

/*============================================================================ 
 
    fftmisc.c  -  Don Cross  
 
    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  
#include  
#include  
 
#include  
 
#define TRUE  1 
#define FALSE 0 
 
#define BITS_PER_WORD   (sizeof(unsigned) * 8) 
 
 
int IsPowerOfTwo ( unsigned x ) 
{ 
    if ( x < 2 ) 
        return FALSE; 
 
    if ( x & (x-1) )        // Thanks to 'byang' for this cute trick! 
        return FALSE; 
 
    return TRUE; 
} 
 
 
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; 
    } 
} 
 
 
 
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---*/