/*
 * This program regenerates a G.711 A-law encoding table equivalent to the
 * s2a[] table in the toast_alaw.c module in libgsm/toast; the intent is
 * to check that table for correctness.  The "engine" function that does
 * the computation is based on alaw_compress() from ITU-T G.191 STL.
 */

#include <stdio.h>
#include <stdlib.h>

static unsigned
alaw_compress (input)
    unsigned input;
{
    short ix, iexp;

    ix = input >= 2048          /* 0 <= ix < 2048 */
      ? ~input & 2047           /* 1's complement for negative values */
      : input;

    /* Do more, if exponent > 0 */
    if (ix > 15) {              /* exponent=0 for ix <= 15 */
      iexp = 1;                 /* first step: */
      while (ix > 16 + 15) {    /* find mantissa and exponent */
        ix >>= 1;
        iexp++;
      }
      ix -= 16;                 /* second step: remove leading '1' */

      ix += iexp << 4;          /* now compute encoded value */
    }
    if (input < 2048)
      ix |= (0x0080);           /* add sign bit */

    return ix ^ (0x0055);       /* toggle even bits */
}

main(argc, argv)
	char **argv;
{
	unsigned input, output;

	for (input = 0; input < 4096; input++) {
		if ((input & 15) == 0)
			putchar('\t');
		output = alaw_compress(input);
		printf("%3u,", output);
		if ((input & 15) == 15)
			putchar('\n');
	}
	exit(0);
}