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-rw-r--r--gr-gsm-fr-vocoder/src/lib/gsm/preprocess.c113
1 files changed, 113 insertions, 0 deletions
diff --git a/gr-gsm-fr-vocoder/src/lib/gsm/preprocess.c b/gr-gsm-fr-vocoder/src/lib/gsm/preprocess.c
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index 000000000..99c0709dc
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+++ b/gr-gsm-fr-vocoder/src/lib/gsm/preprocess.c
@@ -0,0 +1,113 @@
+/*
+ * 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;
+ 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;
+}