shithub: libsamplerate

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ref: 5863210e4fe48ad23f4248759a136d7a0a0c223e
parent: 0bacbd931a498ce8d43d350705249e5d1a6342c0
author: Erik de Castro Lopo <[email protected]>
date: Sun Nov 15 09:48:16 EST 2015

tests/calc_snr.c: Fix indexing of FFTW output

--- a/tests/calc_snr.c
+++ b/tests/calc_snr.c
@@ -204,10 +204,19 @@
 
 	fftw_destroy_plan (plan) ;
 
-	/* (k < N/2 rounded up) */
 	maxval = 0.0 ;
 	for (k = 1 ; k < len / 2 ; k++)
-	{	magnitude [k] = sqrt (magnitude [k] * magnitude [k] + magnitude [len - k - 1] * magnitude [len - k - 1]) ;
+	{	/*
+		** From : http://www.fftw.org/doc/Real_002dto_002dReal-Transform-Kinds.html#Real_002dto_002dReal-Transform-Kinds
+		**
+		** FFTW_R2HC computes a real-input DFT with output in “halfcomplex” format, i.e. real and imaginary parts
+		** for a transform of size n stored as:
+		**
+		**      r0, r1, r2, ..., rn/2, i(n+1)/2-1, ..., i2, i1
+		*/
+		double re = magnitude [k] ;
+		double im = magnitude [len - k] ;
+		magnitude [k] = sqrt (re * re + im * im) ;
 		maxval = (maxval < magnitude [k]) ? magnitude [k] : maxval ;
 		} ;