Code for encoding Laplace-distributed variables (doesn't work).

libentcode/Makefile.am

@@ -2,7 +2,7 @@ INCLUDES =
 METASOURCES = AUTO
 lib_LTLIBRARIES = libentcode.la
 libentcode_la_SOURCES = bitrdec.c bitree.c bitrenc.c ecintrin.h entcode.c \
-	entdec.c entenc.c mfrngdec.c mfrngenc.c probdec.c probenc.c probmod.c
+	entdec.c entenc.c laplace.c mfrngdec.c mfrngenc.c probdec.c probenc.c probmod.c
 bin_PROGRAMS = ectest
 ectest_SOURCES = ectest.c
 ectest_LDADD = $(top_builddir)/libentcode/libentcode.la

libentcode/laplace.c

+/* (C) 2007 Jean-Marc Valin, CSIRO
+*/
+/*
+   Redistribution and use in source and binary forms, with or without
+   modification, are permitted provided that the following conditions
+   are met:
+   
+   - Redistributions of source code must retain the above copyright
+   notice, this list of conditions and the following disclaimer.
+   
+   - Redistributions in binary form must reproduce the above copyright
+   notice, this list of conditions and the following disclaimer in the
+   documentation and/or other materials provided with the distribution.
+   
+   - Neither the name of the Xiph.org Foundation nor the names of its
+   contributors may be used to endorse or promote products derived from
+   this software without specific prior written permission.
+   
+   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+   A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR
+   CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+   PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+   PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#include "entenc.h"
+#include "entdec.h"
+#include <stdio.h>
+
+int ec_laplace_get_total(int decay)
+{
+   return (1<<30)/((1<<14) - decay) - (1<<15) + 1;
+}
+
+void ec_laplace_encode(ec_enc *enc, int value, int decay)
+{
+   int i, fl, fs, ft;
+   int s = 0;
+   if (value < 0)
+   {
+      s = 1;
+      value = -value;
+   }
+   ft = ec_laplace_get_total(decay);
+   fl = -(1<<15);
+   fs = 1<<15;
+   for (i=0;i<value;i++)
+   {
+      fl += fs*2;
+      fs = (fs*decay)>>14;
+   }
+   if (fl < 0)
+      fl = 0;
+   if (s)
+      fl += fs;
+   printf ("enc: %d %d %d\n", fl, fs, ft);
+   ec_encode(enc, fl, fs, ft);
+}
+
+void ec_laplace_decode(ec_dec *dec, int decay)
+{
+   int fl, fh, fs, ft, fm;
+   ft = ec_laplace_get_total(decay);
+   
+   fm = ec_decode(dec, ft);
+   printf ("dec: %d/%d\n", fm, ft);
+   //loop on values here to find fl, fh
+   //ec_dec_update(dec, fl, fh, ft);
+}
+
+#if 0
+int main()
+{
+   ec_enc enc;
+   ec_dec dec;
+   ec_byte_buffer buf;
+   
+   ec_byte_writeinit(&buf);
+   ec_enc_init(&enc,&buf);
+   
+   ec_laplace_encode(&enc, 0, 10000);
+   ec_laplace_encode(&enc, 1, 12000);
+   ec_laplace_encode(&enc, -2, 9000);
+   
+   ec_enc_done(&enc);
+
+   ec_byte_readinit(&buf,ec_byte_get_buffer(&buf),ec_byte_bytes(&buf));
+   ec_dec_init(&dec,&buf);
+
+   ec_laplace_decode(&dec, 10000);
+   
+   ec_byte_writeclear(&buf);
+   return 0;
+}
+#endif
+