From 32e0d5f12f72cb35ffcca719029513917c58f3f9 Mon Sep 17 00:00:00 2001
From: Holger Vogt <holger.vogt@uni-due.de>
Date: Fri, 6 Mar 2026 16:31:29 +0100
Subject: [PATCH] Revert "make fft scaling independent from rounding behaviour
 for odd data"

This reverts commit a31ac54200e3872f28500f9762c49f1369898029.
---
 src/frontend/com_fft.c    | 4 ++--
 src/maths/cmaths/cmath4.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/frontend/com_fft.c b/src/frontend/com_fft.c
index 8b74414fc..d3b68056a 100644
--- a/src/frontend/com_fft.c
+++ b/src/frontend/com_fft.c
@@ -63,7 +63,6 @@ com_fft(wordlist *wl)
 
 #ifdef HAVE_LIBFFTW3
     fpts = length/2 + 1;
-    scale = ((double)length)/2.0;
 #else
     /* size of fft input vector is power of two and larger or equal than spice vector */
     N = 1;
@@ -73,7 +72,6 @@ com_fft(wordlist *wl)
         M++;
     }
     fpts = N/2 + 1;
-    scale = ((double)N)/2;
 #endif
 
     win = TMALLOC(double, length);
@@ -180,6 +178,7 @@ com_fft(wordlist *wl)
 
         fftw_execute(plan_forward);
 
+        scale = (double) fpts - 1.0;
         fdvec[i][0].cx_real = out[0][0]/scale/2.0;
         fdvec[i][0].cx_imag = 0.0;
         for (j = 1; j < fpts; j++) {
@@ -216,6 +215,7 @@ com_fft(wordlist *wl)
         rffts(in, M, 1);
         fftFree();
 
+        scale = (double) fpts - 1.0;
         /* Re(x[0]), Re(x[N/2]), Re(x[1]), Im(x[1]), Re(x[2]), Im(x[2]), ... Re(x[N/2-1]), Im(x[N/2-1]). */
         fdvec[i][0].cx_real = in[0]/scale/2.0;
         fdvec[i][0].cx_imag = 0.0;
diff --git a/src/maths/cmaths/cmath4.c b/src/maths/cmaths/cmath4.c
index 04b0b5142..af661e968 100644
--- a/src/maths/cmaths/cmath4.c
+++ b/src/maths/cmaths/cmath4.c
@@ -774,7 +774,7 @@ cx_fft(void *data, short int type, int length, int *newlength, short int *newtyp
 
         fftw_execute(plan_forward);
 
-        scale = ((double)length)/2.0;
+        scale = (double) fpts - 1.0;
         outdata[0].cx_real = out[0][0]/scale/2.0;
         outdata[0].cx_imag = 0.0;
         for (i = 1; i < fpts; i++) {
@@ -803,7 +803,7 @@ cx_fft(void *data, short int type, int length, int *newlength, short int *newtyp
         rffts(datax, M, 1);
         fftFree();
 
-        scale = ((double)N)/2;
+        scale = (double) fpts - 1.0;
         /* Re(x[0]), Re(x[N/2]), Re(x[1]), Im(x[1]), Re(x[2]), Im(x[2]), ... Re(x[N/2-1]), Im(x[N/2-1]). */
         outdata[0].cx_real = datax[0]/scale/2.0;
         outdata[0].cx_imag = 0.0;