--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/intercom/gsm/preproce.c	Fri Jun 25 09:57:52 2010 +0200
@@ -0,0 +1,111 @@
+/*
+ * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
+ * Universitaet Berlin.  See the accompanying file "COPYRIGHT" for
+ * details.  THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
+ */
+
+/* $Header: /home/kbs/jutta/src/gsm/gsm-1.0/src/RCS/preprocess.c,v 1.1 1992/10/28 00:15:50 jutta Exp $ */
+
+#include	<stdio.h>
+#include	<assert.h>
+
+#include "private.h"
+
+#include	"gsm.h"
+#include 	"proto.h"
+
+/*	4.2.0 .. 4.2.3	PREPROCESSING SECTION
+ *  
+ *  	After A-law to linear conversion (or directly from the
+ *   	Ato D converter) the following scaling is assumed for
+ * 	input to the RPE-LTP algorithm:
+ *
+ *      in:  0.1.....................12
+ *	     S.v.v.v.v.v.v.v.v.v.v.v.v.*.*.*
+ *
+ *	Where S is the sign bit, v a valid bit, and * a "don't care" bit.
+ * 	The original signal is called sop[..]
+ *
+ *      out:   0.1................... 12 
+ *	     S.S.v.v.v.v.v.v.v.v.v.v.v.v.0.0
+ */
+
+
+void Gsm_Preprocess P3((S, s, so),
+  struct gsm_state *S, word * s, word * so)
+{                               /* [0..159]       IN/OUT  */
+
+  word z1 = S->z1;
+  longword L_z2 = S->L_z2;
+  word mp = S->mp;
+
+  word s1;
+  longword L_s2;
+
+  longword L_temp;
+
+  word msp, lsp;
+  word SO;
+
+  longword ltmp;                /* for   ADD */
+  ulongword utmp;               /* for L_ADD */
+
+  register int k = 160;
+
+  while (k--) {
+
+    /*  4.2.1   Downscaling of the input signal
+     */
+    SO = SASR(*s, 3) << 2;
+    s++;
+
+    assert(SO >= -0x4000);      /* downscaled by     */
+    assert(SO <= 0x3FFC);       /* previous routine. */
+
+
+    /*  4.2.2   Offset compensation
+     * 
+     *  This part implements a high-pass filter and requires extended
+     *  arithmetic precision for the recursive part of this filter.
+     *  The input of this procedure is the array so[0...159] and the
+     *  output the array sof[ 0...159 ].
+     */
+    /*   Compute the non-recursive part
+     */
+
+    s1 = SO - z1;               /* s1 = gsm_sub( *so, z1 ); */
+    z1 = SO;
+
+    assert(s1 != MIN_WORD);
+
+    /*   Compute the recursive part
+     */
+    L_s2 = s1;
+    L_s2 <<= 15;
+
+    /*   Execution of a 31 bv 16 bits multiplication
+     */
+
+    msp = SASR(L_z2, 15);
+    lsp = L_z2 - ((longword) msp << 15);        /* gsm_L_sub(L_z2,(msp<<15)); */
+
+    L_s2 += GSM_MULT_R(lsp, 32735);
+    L_temp = (longword) msp *32735;     /* GSM_L_MULT(msp,32735) >> 1; */
+    L_z2 = GSM_L_ADD(L_temp, L_s2);
+
+    /*    Compute sof[k] with rounding
+     */
+    L_temp = GSM_L_ADD(L_z2, 16384);
+
+    /*   4.2.3  Preemphasis
+     */
+
+    msp = GSM_MULT_R(mp, -28180);
+    mp = SASR(L_temp, 15);
+    *so++ = GSM_ADD(mp, msp);
+  }
+
+  S->z1 = z1;
+  S->L_z2 = L_z2;
+  S->mp = mp;
+}