[FFmpeg-devel] [PATCH] hardcoded ff_cos tables

Reimar Döffinger Reimar.Doeffinger
Wed Oct 14 09:53:10 CEST 2009


On Tue, Oct 13, 2009 at 02:41:33PM +0200, Reimar D?ffinger wrote:
> On Tue, Oct 13, 2009 at 01:29:39PM +0100, M?ns Rullg?rd wrote:
> > Reimar D?ffinger <Reimar.Doeffinger at gmx.de> writes:
> > > attached patch allows hardcoding the ff_cos tables so they are in
> > > .rodata instead of .bss.
> > > Not included is the cos_tables.h file as generated by costablegen.c
> > > since it is > 1.7 MB.
> > > Which I admit is a bit of an issue, including this file directly into
> > > SVN is not all that great, but it would be the simplest solution by far...
> > 
> > We could generate the tables at build time.
> 
> Not with this patch, since that reuses the libavcodec/fft.c code to
> generate them, which will be disabled with hardcoded tables enabled.
> It is of course possible to just duplicate the code from
> libavcodec/fft.c, but that is not that beautiful either...

Ok, so here is the version using that approach.
I moved the code to libavcodec, I think it works better for handling the
dependencies and also is better for projects that import libavcodec
directly.
-------------- next part --------------
Index: libavcodec/dsputil.h
===================================================================
--- libavcodec/dsputil.h	(revision 20231)
+++ libavcodec/dsputil.h	(working copy)
@@ -742,7 +742,11 @@
 #define FF_MDCT_PERM_INTERLEAVE 1
 } FFTContext;
 
+#if CONFIG_HARDCODED_TABLES
+extern const FFTSample* const ff_cos_tabs[13];
+#else
 extern FFTSample* const ff_cos_tabs[13];
+#endif
 
 /**
  * Sets up a complex FFT.
Index: libavcodec/Makefile
===================================================================
--- libavcodec/Makefile	(revision 20231)
+++ libavcodec/Makefile	(working copy)
@@ -27,7 +27,7 @@
 # parts needed for many different codecs
 OBJS-$(CONFIG_AANDCT)                  += aandcttab.o
 OBJS-$(CONFIG_ENCODERS)                += faandct.o jfdctfst.o jfdctint.o
-OBJS-$(CONFIG_FFT)                     += fft.o
+OBJS-$(CONFIG_FFT)                     += fft.o cos_tables.h
 OBJS-$(CONFIG_GOLOMB)                  += golomb.o
 OBJS-$(CONFIG_MDCT)                    += mdct.o
 OBJS-$(CONFIG_RDFT)                    += rdft.o
@@ -574,3 +574,5 @@
 include $(SUBDIR)../subdir.mak
 
 $(SUBDIR)dct-test$(EXESUF): $(SUBDIR)dctref.o
+cos_tables.h: costablegen
+	./costablegen > cos_tables.h
Index: libavcodec/costablegen.c
===================================================================
--- libavcodec/costablegen.c	(revision 0)
+++ libavcodec/costablegen.c	(revision 0)
@@ -0,0 +1,46 @@
+/*
+ * Generate a header file for hardcoded ff_cos_* tables
+ *
+ * Copyright (c) 2009 Reimar D?ffinger <Reimar.Doeffinger at gmx.de>
+ *
+ * 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 <stdio.h>
+#include "libavutil/mathematics.h"
+#undef fprintf
+#define BITS 16
+#define FLOATFMT "%.18e"
+int main(void)
+{
+    int i, j;
+    FILE *table = stdout;
+    fprintf(table, "/* This file was generated by tools/costablegen */\n");
+    fprintf(table, "#include \"dsputil.h\"\n");
+    for (i = 4; i <= BITS; i++) {
+        int m = 1 << i;
+        double freq = 2*M_PI/m;
+        fprintf(table, "const FFTSample ff_cos_%i[] = {\n   ", m);
+        for (j = 0; j < m/2 - 1; j++) {
+            int idx = j > m/4 ? m/2 - j : j;
+            fprintf(table, " "FLOATFMT",", cos(idx*freq));
+            if ((j & 3) == 3)
+                fprintf(table, "\n   ");
+        }
+        fprintf(table, " "FLOATFMT"\n};\n", cos(freq));
+    }
+    return 0;
+}
Index: libavcodec/fft.c
===================================================================
--- libavcodec/fft.c	(revision 20231)
+++ libavcodec/fft.c	(working copy)
@@ -28,6 +28,7 @@
 
 #include "dsputil.h"
 
+#if !CONFIG_HARDCODED_TABLES
 /* cos(2*pi*x/n) for 0<=x<=n/4, followed by its reverse */
 DECLARE_ALIGNED_16(FFTSample, ff_cos_16[8]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_32[16]);
@@ -42,6 +43,10 @@
 DECLARE_ALIGNED_16(FFTSample, ff_cos_16384[8192]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_32768[16384]);
 DECLARE_ALIGNED_16(FFTSample, ff_cos_65536[32768]);
+#else
+#include "cos_tables.h"
+const
+#endif
 FFTSample * const ff_cos_tabs[] = {
     ff_cos_16, ff_cos_32, ff_cos_64, ff_cos_128, ff_cos_256, ff_cos_512, ff_cos_1024,
     ff_cos_2048, ff_cos_4096, ff_cos_8192, ff_cos_16384, ff_cos_32768, ff_cos_65536,
@@ -93,6 +98,7 @@
     if (HAVE_MMX)     ff_fft_init_mmx(s);
 
     if (s->split_radix) {
+#if !CONFIG_HARDCODED_TABLES
         for(j=4; j<=nbits; j++) {
             int m = 1<<j;
             double freq = 2*M_PI/m;
@@ -102,6 +108,7 @@
             for(i=1; i<m/4; i++)
                 tab[m/2-i] = tab[i];
         }
+#endif
         for(i=0; i<n; i++)
             s->revtab[-split_radix_permutation(i, n, s->inverse) & (n-1)] = i;
         s->tmp_buf = av_malloc(n * sizeof(FFTComplex));



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