dumping the first 5 values from the window after returning from av_rdft_calc:

reference:
rdft: 24.383970 -0.191442 -14.634604 5.516693 -0.270062
rdft: 9.806152 0.368497 -3.376606 -18.072319 3.183172
rdft: -0.213631 -0.239522 2.430629 12.024548 -1.634596
rdft: 0.559616 -0.096376 -0.009430 -11.425549 -0.792466
rdft: -3.327744 0.205107 -0.028977 6.347848 8.127883

buggy:
rdft: 24.376629 -4.166753 -14.641275 5.516221 -0.27646208 
rdft: 9.811465 8.98779 -3.3706634 -18.071543 3.1885753 
rdft: -0.22264719 -6.2187924 2.4217222 12.023994 -1.643787 
rdft: 0.5557308 -2.1821938 -0.013725936 -11.425043 -0.79600334 
rdft: -3.327513 4.1963043 -0.02909863 6.3476887 8.127403