--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libgsmfr2/add.c	Sun Apr 14 00:06:50 2024 +0000
@@ -0,0 +1,233 @@
+/*
+ * This C source file has been adapted from TU-Berlin libgsm source,
+ * original notice follows:
+ *
+ * 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.
+ */
+
+#include <stdint.h>
+#include <assert.h>
+#include <string.h>
+#include "tw_gsmfr.h"
+#include "typedef.h"
+#include "ed_state.h"
+#include "ed_internal.h"
+
+#define	saturate(x) 	\
+	((x) < MIN_WORD ? MIN_WORD : (x) > MAX_WORD ? MAX_WORD: (x))
+
+word gsm_add (word a, word b)
+{
+	longword sum = (longword)a + (longword)b;
+	return saturate(sum);
+}
+
+word gsm_sub (word a, word b)
+{
+	longword diff = (longword)a - (longword)b;
+	return saturate(diff);
+}
+
+word gsm_mult (word a, word b)
+{
+	if (a == MIN_WORD && b == MIN_WORD) return MAX_WORD;
+	else return SASR( (longword)a * (longword)b, 15 );
+}
+
+word gsm_mult_r (word a, word b)
+{
+	if (b == MIN_WORD && a == MIN_WORD) return MAX_WORD;
+	else {
+		longword prod = (longword)a * (longword)b + 16384;
+		prod >>= 15;
+		return prod & 0xFFFF;
+	}
+}
+
+word gsm_abs (word a)
+{
+	return a < 0 ? (a == MIN_WORD ? MAX_WORD : -a) : a;
+}
+
+longword gsm_L_mult (word a, word b)
+{
+	assert( a != MIN_WORD || b != MIN_WORD );
+	return ((longword)a * (longword)b) << 1;
+}
+
+longword gsm_L_add (longword a, longword b)
+{
+	if (a < 0) {
+		if (b >= 0) return a + b;
+		else {
+			ulongword A = (ulongword)-(a + 1) + (ulongword)-(b + 1);
+			return A >= MAX_LONGWORD ? MIN_LONGWORD :-(longword)A-2;
+		}
+	}
+	else if (b <= 0) return a + b;
+	else {
+		ulongword A = (ulongword)a + (ulongword)b;
+		return A > MAX_LONGWORD ? MAX_LONGWORD : A;
+	}
+}
+
+longword gsm_L_sub (longword a, longword b)
+{
+	if (a >= 0) {
+		if (b >= 0) return a - b;
+		else {
+			/* a>=0, b<0 */
+
+			ulongword A = (ulongword)a + -(b + 1);
+			return A >= MAX_LONGWORD ? MAX_LONGWORD : (A + 1);
+		}
+	}
+	else if (b <= 0) return a - b;
+	else {
+		/* a<0, b>0 */
+
+		ulongword A = (ulongword)-(a + 1) + b;
+		return A >= MAX_LONGWORD ? MIN_LONGWORD : -(longword)A - 1;
+	}
+}
+
+static unsigned char const bitoff[ 256 ] = {
+	 8, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
+	 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
+	 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+	 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+	 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+	 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+	 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+	 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+	 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+};
+
+word gsm_norm (longword a)
+/*
+ * the number of left shifts needed to normalize the 32 bit
+ * variable L_var1 for positive values on the interval
+ *
+ * with minimum of
+ * minimum of 1073741824  (01000000000000000000000000000000) and
+ * maximum of 2147483647  (01111111111111111111111111111111)
+ *
+ *
+ * and for negative values on the interval with
+ * minimum of -2147483648 (-10000000000000000000000000000000) and
+ * maximum of -1073741824 ( -1000000000000000000000000000000).
+ *
+ * in order to normalize the result, the following
+ * operation must be done: L_norm_var1 = L_var1 << norm( L_var1 );
+ *
+ * (That's 'ffs', only from the left, not the right..)
+ */
+{
+	assert(a != 0);
+
+	if (a < 0) {
+		if (a <= -1073741824) return 0;
+		a = ~a;
+	}
+
+	return    a & 0xffff0000
+		? ( a & 0xff000000
+		  ?  -1 + bitoff[ 0xFF & (a >> 24) ]
+		  :   7 + bitoff[ 0xFF & (a >> 16) ] )
+		: ( a & 0xff00
+		  ?  15 + bitoff[ 0xFF & (a >> 8) ]
+		  :  23 + bitoff[ 0xFF & a ] );
+}
+
+longword gsm_L_asl (longword a, int n)
+{
+	if (n >= 32) return 0;
+	if (n <= -32) return -(a < 0);
+	if (n < 0) return gsm_L_asr(a, -n);
+	return a << n;
+}
+
+word gsm_asl (word a, int n)
+{
+	if (n >= 16) return 0;
+	if (n <= -16) return -(a < 0);
+	if (n < 0) return gsm_asr(a, -n);
+	return a << n;
+}
+
+longword gsm_L_asr (longword a, int n)
+{
+	if (n >= 32) return -(a < 0);
+	if (n <= -32) return 0;
+	if (n < 0) return a << -n;
+
+#	ifdef	SASR
+		return a >> n;
+#	else
+		if (a >= 0) return a >> n;
+		else return -(longword)( -(ulongword)a >> n );
+#	endif
+}
+
+word gsm_asr (word a, int n)
+{
+	if (n >= 16) return -(a < 0);
+	if (n <= -16) return 0;
+	if (n < 0) return a << -n;
+
+#	ifdef	SASR
+		return a >> n;
+#	else
+		if (a >= 0) return a >> n;
+		else return -(word)( -(uword)a >> n );
+#	endif
+}
+
+/*
+ *  (From p. 46, end of section 4.2.5)
+ *
+ *  NOTE: The following lines gives [sic] one correct implementation
+ *  	  of the div(num, denum) arithmetic operation.  Compute div
+ *        which is the integer division of num by denum: with denum
+ *	  >= num > 0
+ */
+
+word gsm_div (word num, word denum)
+{
+	longword	L_num   = num;
+	longword	L_denum = denum;
+	word		div 	= 0;
+	int		k 	= 15;
+
+	/* The parameter num sometimes becomes zero.
+	 * Although this is explicitly guarded against in 4.2.5,
+	 * we assume that the result should then be zero as well.
+	 */
+
+	/* assert(num != 0); */
+
+	assert(num >= 0 && denum >= num);
+	if (num == 0)
+	    return 0;
+
+	while (k--) {
+		div   <<= 1;
+		L_num <<= 1;
+
+		if (L_num >= L_denum) {
+			L_num -= L_denum;
+			div++;
+		}
+	}
+
+	return div;
+}