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 /*============================================================================ 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 "fourier.h" #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---*/