/*TITLE adaptive modeling routines */

/****keyword-flag*** "%v %f %n" */
/* "16 30-May-94,9:24:34 ADAPT.C" */

#include <malloc.h>
#include "model.h"

#define INIT_INDEX 7 /* where a new character starts out the first time */

#define BOTH_WEIGHTS_ZERO 2 /* this must be the total of two "unused" weights */
/* and must be the same for both (or all) translate tables */

unsigned translate[TRANSLATE_SIZE] = TRANSLATE_TABLE;

unsigned char upgrade_threshold[TRANSLATE_SIZE];

/* all possible combinations of 2 low weights */
unsigned both_weights[TRANSLATE_SIZE*TRANSLATE_SIZE];

unsigned symbol_translation[NO_OF_CHARS] = {32,101,116,111,97,105,110,114,115,
104,108,100,13,10,99,117,109,112,103,121,102,46,98,119,44,94,118,107,78,84,
69,39,65,83,41,40,120,66,45,73,34,77,58,80,85,67,49,82,48,87,79,47,88,72,
70,68,89,57,71,113,76,50,86,122,106,59,63,54,55,74,61,42,37,12,53,64,56,75,
33,52,51,90,62,38,81,35,26,255,254,253,252,251,250,249,248,247,246,245,244,
243,242,241,240,239,238,237,236,235,234,233,232,231,230,229,228,227,226,225,
224,223,222,221,220,219,218,217,216,215,214,213,212,211,210,209,208,207,206,
205,204,203,202,201,200,199,198,197,196,195,194,193,192,191,190,189,188,187,
186,185,184,183,182,181,180,179,178,177,176,175,174,173,172,171,170,169,168,
167,166,165,164,163,162,161,160,159,158,157,156,155,154,153,152,151,150,149,
148,147,146,145,144,143,142,141,140,139,138,137,136,135,134,133,132,131,130,
129,128,127,126,125,124,123,96,95,93,92,91,60,43,36,31,30,29,28,27,25,24,23,
22,21,20,19,18,17,16,15,14,11,9,8,7,6,5,4,3,2,1,0};

unsigned char_translation[NO_OF_CHARS];

FrequencyInfo frequency_info_data[NO_OF_CHARS];
FrequencyInfo *frequency_info[NO_OF_CHARS];

unsigned char char_total;

start_model()
{
	int i;
	int j;
	double temp_threshold;

	for (i = 0; i < TRANSLATE_SIZE - 1; i ++)
		{
		temp_threshold = 256*(1-(double)translate[i]/(double)translate[i+1]);
		upgrade_threshold[i] = (unsigned char)temp_threshold;
		}

	upgrade_threshold[TRANSLATE_SIZE-1] = 255;
	char_total = 0;

	for (i = 0; i < TRANSLATE_SIZE; i ++)
		for (j = 0; j < TRANSLATE_SIZE; j ++)
			both_weights[TRANSLATE_SIZE*i+j] = translate[i] + translate[j];

	for (i = 0; i < NO_OF_CHARS; i ++)
		{
		frequency_info[i] = &frequency_info_data[i];
		for (j = 0; j < (NO_OF_SYMBOLS+1+1)/2; j ++)
			frequency_info[i]->freq[j] = 0;
		frequency_info[i]->total_freq = translate[0] * (NO_OF_SYMBOLS + 1);
		}

	for (i = 0; i < NO_OF_CHARS; i ++)
		char_translation[symbol_translation[i]] = i;

	return(0);
}

update_model(int symbol,unsigned char oldch)
{
	int i;
	int index;
	unsigned char *freq_ptr;
	unsigned char freq;
	int old_weight_code;
	unsigned weight_gain;
	unsigned char temp_freq;
	long temp_total_freq;
	FrequencyInfo *temp_freq_info;
	unsigned char low_symbol;

	low_symbol = (unsigned char)(symbol_translation[symbol] & 255);

	char_total = (unsigned char)(char_total + low_symbol);

	old_weight_code = -1;
	temp_freq_info = frequency_info[oldch];
	freq_ptr = temp_freq_info->freq;
	index = symbol/2;
	if (symbol % 2 == 0) /* if a high symbol */
		{
		temp_freq = 
			(unsigned char)((freq_ptr[index] & HIGH_MASK) >> HIGH_SHIFT);
		if (temp_freq == 0)
			{
			freq_ptr[index] += INIT_INDEX << HIGH_SHIFT;
			temp_freq_info->total_freq += 
			translate[INIT_INDEX] - translate[0];
			}
		else if (char_total > upgrade_threshold[temp_freq])
			{
			old_weight_code = temp_freq;
			freq_ptr[index] += HIGH_INCREMENT; /* bump it */
			}
		}
	else /* if a low one */
		{
		temp_freq = (unsigned char)((freq_ptr[index] & LOW_MASK) >> LOW_SHIFT);
		if (temp_freq == 0)
			{
			freq_ptr[index] += INIT_INDEX << LOW_SHIFT;
			temp_freq_info->total_freq += 
			translate[INIT_INDEX] - translate[0];
			}
		else if (char_total > upgrade_threshold[temp_freq])
			{
			old_weight_code = temp_freq;
			freq_ptr[index] += LOW_INCREMENT; /* bump it */
			}
		}

	if (old_weight_code != -1) /* if there was an adjustment of weight */
		{
		weight_gain = translate[old_weight_code+1] - translate[old_weight_code];
		temp_freq_info->total_freq += weight_gain;
		}

	temp_total_freq = temp_freq_info->total_freq;
	while (temp_total_freq > MAX_FREQUENCY)
		{
		temp_total_freq = 0;
		freq_ptr = temp_freq_info->freq;
		for (i = 0; i < (NO_OF_SYMBOLS+1)/2; i ++)
			{
			if (*freq_ptr == 0) /* if this is at the bottom, forget it */
				temp_total_freq += BOTH_WEIGHTS_ZERO;
			else /* if it needs to be updated */
				{
				freq = *freq_ptr;
				if ((freq & HIGH_MASK) != 0)
					{
					/* if the top is not at the lowest value*/
					*freq_ptr -= HIGH_INCREMENT; /* decrement it */
					}
				if ((freq & LOW_MASK) != 0)
					{
					/* if the low is not at the lowest value*/
					*freq_ptr -= LOW_INCREMENT; /* decrement it */
					}
				temp_total_freq += both_weights[*freq_ptr];
				}
			freq_ptr ++;
			}
		}
	temp_freq_info->total_freq = (unsigned)temp_total_freq;
	return(0);
}