--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/agc.c	Wed Apr 03 05:31:37 2024 +0000
@@ -0,0 +1,186 @@
+/*************************************************************************
+ *
+ *  FUNCTION:  agc
+ *
+ *  PURPOSE: Scales the postfilter output on a subframe basis by automatic
+ *           control of the subframe gain.
+ *
+ *  DESCRIPTION:
+ *   sig_out[n] = sig_out[n] * gain[n];
+ *   where gain[n] is the gain at the nth sample given by
+ *     gain[n] = agc_fac * gain[n-1] + (1 - agc_fac) g_in/g_out
+ *   g_in/g_out is the square root of the ratio of energy at the input
+ *   and output of the postfilter.
+ *
+ *************************************************************************/
+
+#include "typedef.h"
+#include "basic_op.h"
+#include "count.h"
+#include "sig_proc.h"
+#include "cnst.h"
+
+Word16 past_gain;               /* initial value of past_gain = 1.0  */
+
+void agc (
+    Word16 *sig_in,             /* (i)     : postfilter input signal  */
+    Word16 *sig_out,            /* (i/o)   : postfilter output signal */
+    Word16 agc_fac,             /* (i)     : AGC factor               */
+    Word16 l_trm                /* (i)     : subframe size            */
+)
+{
+    Word16 i, exp;
+    Word16 gain_in, gain_out, g0, gain;
+    Word32 s;
+
+    Word16 temp;
+
+    /* calculate gain_out with exponent */
+
+    temp = shr (sig_out[0], 2);
+    s = L_mult (temp, temp);
+
+    for (i = 1; i < l_trm; i++)
+    {
+        temp = shr (sig_out[i], 2);
+        s = L_mac (s, temp, temp);
+    }
+
+    test (); 
+    if (s == 0)
+    {
+        past_gain = 0;          move16 (); 
+        return;
+    }
+    exp = sub (norm_l (s), 1);
+    gain_out = round (L_shl (s, exp));
+
+    /* calculate gain_in with exponent */
+
+    temp = shr (sig_in[0], 2);
+    s = L_mult (temp, temp);
+
+    for (i = 1; i < l_trm; i++)
+    {
+        temp = shr (sig_in[i], 2);
+        s = L_mac (s, temp, temp);
+    }
+
+    test (); 
+    if (s == 0)
+    {
+        g0 = 0;                 move16 (); 
+    }
+    else
+    {
+        i = norm_l (s);
+        gain_in = round (L_shl (s, i));
+        exp = sub (exp, i);
+
+        /*---------------------------------------------------*
+         *  g0 = (1-agc_fac) * sqrt(gain_in/gain_out);       *
+         *---------------------------------------------------*/
+
+        s = L_deposit_l (div_s (gain_out, gain_in));
+        s = L_shl (s, 7);       /* s = gain_out / gain_in */
+        s = L_shr (s, exp);     /* add exponent */
+
+        s = Inv_sqrt (s);
+        i = round (L_shl (s, 9));
+
+        /* g0 = i * (1-agc_fac) */
+        g0 = mult (i, sub (32767, agc_fac));
+    }
+
+    /* compute gain[n] = agc_fac * gain[n-1]
+                        + (1-agc_fac) * sqrt(gain_in/gain_out) */
+    /* sig_out[n] = gain[n] * sig_out[n]                        */
+
+    gain = past_gain;           move16 (); 
+
+    for (i = 0; i < l_trm; i++)
+    {
+        gain = mult (gain, agc_fac);
+        gain = add (gain, g0);
+        sig_out[i] = extract_h (L_shl (L_mult (sig_out[i], gain), 3));
+                                move16 (); 
+    }
+
+    past_gain = gain;           move16 (); 
+
+    return;
+}
+
+void agc2 (
+ Word16 *sig_in,        /* (i)     : postfilter input signal  */
+ Word16 *sig_out,       /* (i/o)   : postfilter output signal */
+ Word16 l_trm           /* (i)     : subframe size            */
+)
+{
+    Word16 i, exp;
+    Word16 gain_in, gain_out, g0;
+    Word32 s;
+
+    Word16 temp;
+
+    /* calculate gain_out with exponent */
+
+    temp = shr (sig_out[0], 2);
+    s = L_mult (temp, temp);
+    for (i = 1; i < l_trm; i++)
+    {
+        temp = shr (sig_out[i], 2);
+        s = L_mac (s, temp, temp);
+    }
+
+    test (); 
+    if (s == 0)
+    {
+        return;
+    }
+    exp = sub (norm_l (s), 1);
+    gain_out = round (L_shl (s, exp));
+
+    /* calculate gain_in with exponent */
+
+    temp = shr (sig_in[0], 2);
+    s = L_mult (temp, temp);
+    for (i = 1; i < l_trm; i++)
+    {
+        temp = shr (sig_in[i], 2);
+        s = L_mac (s, temp, temp);
+    }
+
+    test (); 
+    if (s == 0)
+    {
+        g0 = 0;                 move16 (); 
+    }
+    else
+    {
+        i = norm_l (s);
+        gain_in = round (L_shl (s, i));
+        exp = sub (exp, i);
+
+        /*---------------------------------------------------*
+         *  g0 = sqrt(gain_in/gain_out);                     *
+         *---------------------------------------------------*/
+
+        s = L_deposit_l (div_s (gain_out, gain_in));
+        s = L_shl (s, 7);       /* s = gain_out / gain_in */
+        s = L_shr (s, exp);     /* add exponent */
+
+        s = Inv_sqrt (s);
+        g0 = round (L_shl (s, 9));
+    }
+
+    /* sig_out(n) = gain(n) sig_out(n) */
+
+    for (i = 0; i < l_trm; i++)
+    {
+        sig_out[i] = extract_h (L_shl (L_mult (sig_out[i], g0), 3));
+                                move16 (); 
+    }
+
+    return;
+}