ref: 116bd1b775471efeec4a96d59d108c9c791fc89c
parent: d21a4b16afd6d962be45604f2681e2346695e159
author: Paul Brossier <piem@piem.org>
date: Tue Feb 16 12:47:43 EST 2016
src/mathutils.h: add fvec_ishift
--- a/src/mathutils.c
+++ b/src/mathutils.c
@@ -253,15 +253,41 @@
void
fvec_shift (fvec_t * s)
{+ uint_t half = s->length / 2, start = half;
+ // if length is odd, middle element is moved to the end
+ if (2 * half < s->length) start ++;
#ifndef HAVE_ATLAS
- uint_t j;
- for (j = 0; j < s->length / 2; j++) {- ELEM_SWAP (s->data[j], s->data[j + s->length / 2]);
+ for (uint_t j = 0; j < half; j++) {+ ELEM_SWAP (s->data[j], s->data[j + start]);
}
#else
- uint_t half = s->length / 2;
- aubio_cblas_swap(half, s->data, 1, s->data + half, 1);
+ aubio_cblas_swap(half, s->data, 1, s->data + start, 1);
#endif
+ if (start != half) {+ for (uint_t j = 0; j < half; j++) {+ ELEM_SWAP (s->data[j + start - 1], s->data[j + start]);
+ }
+ }
+}
+
+void
+fvec_ishift (fvec_t * s)
+{+ uint_t half = s->length / 2, start = half;
+ // if length is odd, middle element is moved to the beginning
+ if (2 * half < s->length) start ++;
+#ifndef HAVE_ATLAS
+ for (uint_t j = 0; j < half; j++) {+ ELEM_SWAP (s->data[j], s->data[j + start]);
+ }
+#else
+ aubio_cblas_swap(half, s->data, 1, s->data + start, 1);
+#endif
+ if (start != half) {+ for (uint_t j = 0; j < half; j++) {+ ELEM_SWAP (s->data[half], s->data[j]);
+ }
+ }
}
smpl_t
--- a/src/mathutils.h
+++ b/src/mathutils.h
@@ -99,6 +99,24 @@
*/
void fvec_shift (fvec_t * v);
+/** swap the left and right halves of a vector
+
+ This function swaps the left part of the signal with the right part of the
+signal. Therefore
+
+ \f$ a[0], a[1], ..., a[\frac{N}{2}], a[\frac{N}{2}+1], ..., a[N-1], a[N] \f$+
+ becomes
+
+ \f$ a[\frac{N}{2}+1], ..., a[N-1], a[N], a[0], a[1], ..., a[\frac{N}{2}] \f$+
+ This operation, known as 'ifftshift' in the Matlab Signal Processing Toolbox,
+can be used after computing the inverse FFT to simplify the phase relationship
+of the resulting spectrum. See Amalia de Götzen's paper referred to above.
+
+*/
+void fvec_ishift (fvec_t * v);
+
/** compute the sum of all elements of a vector
\param v vector to compute the sum of