1 files changed, 127 insertions, 0 deletions
diff --git a/trunk/codecs/gsm/src/preprocess.c b/trunk/codecs/gsm/src/preprocess.c
new file mode 100644
index 000000000..eacdac851
--- /dev/null
+++ b/trunk/codecs/gsm/src/preprocess.c
@@ -0,0 +1,127 @@
+/*
+ * 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.
+ */
+
+/* $Header$ */
+
+#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;
+	word		SO;
+	ulongword	utmp;		/* for L_ADD */
+	register int	k = 160;
+
+	(void) utmp;
+
+	while (k--) {
+
+	/*  4.2.1   Downscaling of the input signal
+	 */
+		/* SO = SASR( *s, 3 ) << 2;*/
+		SO = SASR( *s, 1 ) & ~3;
+		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);
+
+	/* SJB Remark: float might be faster than the mess that follows */
+
+		/*   Compute the recursive part
+		 */
+
+		/*   Execution of a 31 bv 16 bits multiplication
+		 */
+		{
+		word		msp;
+#ifndef __GNUC__ 
+		word		lsp;
+#endif
+		longword L_s2;
+		longword L_temp;
+		
+		L_s2 = s1;
+		L_s2 <<= 15;
+#ifndef __GNUC__ 
+		msp = (word)SASR( L_z2, 15 );
+		lsp = (word)(L_z2 & 0x7fff); /* 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 );
+		/* above does L_z2  = L_z2 * 0x7fd5/0x8000 + L_s2 */
+#else
+		L_z2 = ((long long)L_z2*32735 + 0x4000)>>15;
+		/* alternate (ansi) version of above line does slightly different rounding:
+		 * L_temp = L_z2 >> 9;
+		 * L_temp += L_temp >> 5;
+		 * L_temp = (++L_temp) >> 1;
+		 * L_z2 = L_z2 - L_temp;
+		 */
+		L_z2 = GSM_L_ADD(L_z2,L_s2);
+#endif
+		/*    Compute sof[k] with rounding
+		 */
+		L_temp = GSM_L_ADD( L_z2, 16384 );
+
+	/*   4.2.3  Preemphasis
+	 */
+
+		msp   = (word)GSM_MULT_R( mp, -28180 );
+		mp    = (word)SASR( L_temp, 15 );
+		*so++ = GSM_ADD( mp, msp );
+		}
+	}
+
+	S->z1   = z1;
+	S->L_z2 = L_z2;
+	S->mp   = mp;
+}