--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtwamr/preemph.c	Mon May 06 19:19:27 2024 +0000
@@ -0,0 +1,89 @@
+/*
+********************************************************************************
+*
+*      GSM AMR-NB speech codec   R98   Version 7.6.0   December 12, 2001
+*                                R99   Version 3.3.0                
+*                                REL-4 Version 4.1.0                
+*
+********************************************************************************
+*
+*      File             : preemph.c
+*      Purpose          : Preemphasis filtering
+*      Description      : Filtering through 1 - g z^-1 
+*
+********************************************************************************
+*/
+
+/*
+********************************************************************************
+*                         MODULE INCLUDE FILE AND VERSION ID
+********************************************************************************
+*/
+#include "namespace.h"
+#include "preemph.h"
+
+/*
+********************************************************************************
+*                         INCLUDE FILES
+********************************************************************************
+*/
+#include "typedef.h"
+#include "basic_op.h"
+#include "no_count.h"
+
+/*
+********************************************************************************
+*                         LOCAL VARIABLES AND TABLES
+********************************************************************************
+*/
+
+/*
+********************************************************************************
+*                         PUBLIC PROGRAM CODE
+********************************************************************************
+*/
+
+/*************************************************************************
+*
+*  Function:   preemphasis_reset
+*  Purpose:    Initializes state memory to zero
+*
+**************************************************************************
+*/
+void preemphasis_reset (preemphasisState *state)
+{
+  state->mem_pre = 0;
+}
+ 
+/*
+**************************************************************************
+*  Function:  preemphasis
+*  Purpose:   Filtering through 1 - g z^-1 
+*
+**************************************************************************
+*/
+int preemphasis (
+    preemphasisState *st, /* (i/o)  : preemphasis filter state    */
+    Word16 *signal, /* (i/o)   : input signal overwritten by the output */
+    Word16 g,       /* (i)     : preemphasis coefficient                */
+    Word16 L        /* (i)     : size of filtering                      */
+)
+{
+    Word16 *p1, *p2, temp, i;
+
+    p1 = signal + L - 1;                    move16 (); 
+    p2 = p1 - 1;                            move16 (); 
+    temp = *p1;                             move16 (); 
+
+    for (i = 0; i <= L - 2; i++)
+    {
+        *p1 = sub (*p1, mult (g, *p2--));   move16 (); 
+        p1--;
+    }
+
+    *p1 = sub (*p1, mult (g, st->mem_pre));     move16 (); 
+
+    st->mem_pre = temp;                         move16 (); 
+
+    return 0;
+}