--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dev/s2u-regen-plus4.c	Sun Apr 23 17:07:51 2023 +0000
@@ -0,0 +1,73 @@
+/*
+ * This program is a companion to s2u-regen.c: it computes a mu-law encoding
+ * table with 13-bit input just like s2u-regen, but computes it as if the
+ * lsb following the 13-bit part is always 1 rather than always 0.  The
+ * purpose of this program is to illustrate the effect of that lsb on the
+ * mu-law output.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+static unsigned
+ulaw_compress(input)
+    unsigned input;
+{
+    short i;                    /* aux.var. */
+    short absno;                /* absolute value of linear (input) sample */
+    short segno;                /* segment (Table 2/G711, column 1) */
+    short low_nibble;           /* low nibble of log companded sample */
+    short high_nibble;          /* high nibble of log companded sample */
+    unsigned output;
+
+    /* -------------------------------------------------------------------- */
+    /* Input is 14-bit right-justified in this version */
+    /* Compute absolute value; adjust for easy processing */
+    /* -------------------------------------------------------------------- */
+    absno = input >= 0x2000     /* compute 1's complement in case of */
+      ? (~input & 0x1FFF) + 33          /* negative samples */
+      : input + 33;                     /* NB: 33 is the difference value */
+    /* between the thresholds for */
+    /* A-law and u-law. */
+    if (absno > (0x1FFF))       /* limitation to "absno" < 8192 */
+      absno = (0x1FFF);
+
+    /* Determination of sample's segment */
+    i = absno >> 6;
+    segno = 1;
+    while (i != 0) {
+      segno++;
+      i >>= 1;
+    }
+
+    /* Mounting the high-nibble of the log-PCM sample */
+    high_nibble = (0x0008) - segno;
+
+    /* Mounting the low-nibble of the log PCM sample */
+    low_nibble = (absno >> segno)       /* right shift of mantissa and */
+      &(0x000F);                /* masking away leading '1' */
+    low_nibble = (0x000F) - low_nibble;
+
+    /* Joining the high-nibble and the low-nibble of the log PCM sample */
+    output = (high_nibble << 4) | low_nibble;
+
+    /* Add sign bit */
+    if (input < 0x2000)
+      output = output | (0x0080);
+
+    return output;
+}
+
+main(argc, argv)
+	char **argv;
+{
+	unsigned input, output;
+
+	for (input = 0; input < 8192; input++) {
+		output = ulaw_compress((input << 1) + 1);
+		printf("%04o,", output);
+		if ((input % 15) == 14 || input == 8191)
+			putchar('\n');
+	}
+	exit(0);
+}