mdct15: add assembly optimizations for the 15-point FFT

c:    1802 decicycles in fft15,16774635 runs,   2581 skips
avx:   865 decicycles in fft15,16776378 runs,    838 skips

Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>

1 files changed, 95 insertions, 0 deletions

diff --git a/libavcodec/x86/mdct15_init.c b/libavcodec/x86/mdct15_init.c
new file mode 100644
index 0000000000..ba3d94c2ec
--- /dev/null
+++ b/libavcodec/x86/mdct15_init.c
@@ -0,0 +1,95 @@
+/*
+ * SIMD optimized non-power-of-two MDCT functions
+ *
+ * Copyright (C) 2017 Rostislav Pehlivanov <atomnuker@gmail.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "config.h"
+
+#include "libavutil/x86/cpu.h"
+#include "libavcodec/mdct15.h"
+
+void ff_fft15_avx(FFTComplex *out, FFTComplex *in, FFTComplex *exptab, ptrdiff_t stride);
+
+static void perm_twiddles(MDCT15Context *s)
+{
+    int k;
+    FFTComplex exp_5point[4];
+
+    FFTComplex tmp[21], tmp2[30];
+    memcpy(tmp, s->exptab, sizeof(FFTComplex)*21);
+
+    /* 15-point FFT twiddles */
+    for (k = 0; k < 5; k++) {
+        tmp2[6*k + 0] = tmp[k +  0];
+        tmp2[6*k + 2] = tmp[k +  5];
+        tmp2[6*k + 4] = tmp[k + 10];
+
+        tmp2[6*k + 1] = tmp[2 * (k + 0)];
+        tmp2[6*k + 3] = tmp[2 * (k + 5)];
+        tmp2[6*k + 5] = tmp[2 *  k + 5 ];
+    }
+
+    for (k = 0; k < 6; k++) {
+        FFTComplex ac_exp[] = {
+            { tmp2[6*1 + k].re,  tmp2[6*1 + k].re },
+            { tmp2[6*2 + k].re,  tmp2[6*2 + k].re },
+            { tmp2[6*3 + k].re,  tmp2[6*3 + k].re },
+            { tmp2[6*4 + k].re,  tmp2[6*4 + k].re },
+            { tmp2[6*1 + k].im, -tmp2[6*1 + k].im },
+            { tmp2[6*2 + k].im, -tmp2[6*2 + k].im },
+            { tmp2[6*3 + k].im, -tmp2[6*3 + k].im },
+            { tmp2[6*4 + k].im, -tmp2[6*4 + k].im },
+        };
+        memcpy(s->exptab + 8*k, ac_exp, 8*sizeof(FFTComplex));
+    }
+
+    /* Specialcase when k = 0 */
+    for (k = 0; k < 3; k++) {
+        FFTComplex dc_exp[] = {
+            { tmp2[2*k + 0].re, -tmp2[2*k + 0].im },
+            { tmp2[2*k + 0].im,  tmp2[2*k + 0].re },
+            { tmp2[2*k + 1].re, -tmp2[2*k + 1].im },
+            { tmp2[2*k + 1].im,  tmp2[2*k + 1].re },
+        };
+        memcpy(s->exptab + 8*6 + 4*k, dc_exp, 4*sizeof(FFTComplex));
+    }
+
+    /* 5-point FFT twiddles */
+    exp_5point[0].re = exp_5point[0].im = tmp[19].re;
+    exp_5point[1].re = exp_5point[1].im = tmp[19].im;
+    exp_5point[2].re = exp_5point[2].im = tmp[20].re;
+    exp_5point[3].re = exp_5point[3].im = tmp[20].im;
+
+    memcpy(s->exptab + 8*6 + 4*3, exp_5point, 4*sizeof(FFTComplex));
+}
+
+av_cold void ff_mdct15_init_x86(MDCT15Context *s)
+{
+    int adjust_twiddles = 0;
+    int cpu_flags = av_get_cpu_flags();
+
+    if (ARCH_X86_64 && EXTERNAL_AVX(cpu_flags)) {
+        s->fft15 = ff_fft15_avx;
+        adjust_twiddles = 1;
+    }
+
+    if (adjust_twiddles)
+        perm_twiddles(s);
+}