/**
 * Implementation of the TI BASIC PRNG
 * (C) 2009 Tim Hentenaar. http://hentenaar.com
 *
 * Released under the GNU General Public License v3 (or later)
 * See: http://www.gnu.org/licenses/gpl.html for details.
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>

/* These are test results from runs of the GPL Rand function in a TI emulator */
uint16_t gpl_rand_test_results[][2] = {
	{ 0x34, 0xe8dc },
	{ 0x5b, 0x2b85 },
	{ 0x57, 0x13b2 },
	{ 0x4e, 0x46f3 },
	{ 0x17, 0x4f18 },
	{ 0x07, 0xa331 },
	{ 0x20, 0xb48e }
};

/* The first ten sequences generated from RND */
const char *rnd_test_results[10] = {
	".5291877823",
	".3913360723",
	".5343438556",
	".3894551053", 
	".2555008073",
	".5621974824",
	".2553391677",
	".5882911741",
	".7000201301",
	".0010849577",
};

/* Value of the seed after RANDOMIZE */
int32_t randomize_test_results[14][2] = {
	{ 0, 0 },
	{ 1,   0x4001 },
	{ 2,   0x4002 },
	{ 100, 0x4101 },
	{ 200, 0x4102 },
	{ 256, 0x4102 },
	{ 1000, 0x410a },
	{ 1500, 0x410f },
	{ 10000, 0x4201 },
	{ 100000, 0x420a },
	{ 1000000, 0x4301 },
	{ 1506631, 0x4301 },
	{ -1, 0xbfff },
	{ -100, 0xbeff }
};

/* The initial seed */
uint16_t seed = 0x3567;

/* RAND: Generate a pseudo-random number */
uint8_t gpl_rand(uint8_t divisor) {	
	/* Update the seed */
	seed = ((uint32_t)(seed * 0x6fe5) & 0xffff) + 0x7ab9;
	
	/* Swap bytes, and compute modulus */
	return ((((seed & 0xff00) >> 8) | ((seed & 0x00ff) << 8)) % (!divisor ? 1 : divisor));
}

/* Equivalent to PRINT RND in TI Basic */	
char *rnd() {
	uint8_t rnds[7]; int i; char *n; 
	
	/* Try up to 64 times to come up with a non-zero pseudo-random integer */
	for (i=0;i<63;i++) if ((rnds[0] = gpl_rand(100)) != 0) break;
	if (rnds[0] == 0) return strdup("0");
	
	/* Generate the rest of the set */	 
	for (i=1;i<7;i++) rnds[i] = gpl_rand(100);

	/* PRINT rounds up if the 6th number generated is >= 0x32 (50) */
	if (rnds[5] >= 0x32) rnds[4]++;

	/* PRINT prepends a leading zero if the first byte is < 0x10 */
	if (rnds[0] < 0x10) {
		memmove(&rnds[1],&rnds[0],6);
		rnds[0] = 0;
	}

	/* Convert to string */
	n = malloc(22);
	snprintf(n,22,".%02d%02d%02d%02d%02d",rnds[0],rnds[1],rnds[2],rnds[3],rnds[4]);
	return n;
}

/* TI Basic RANDOMIZE */
void randomize(int32_t s) {
	/* Randomize appears to compute the seed this way */
	int ex = 0; uint32_t x = (s < 0) ? (~s+1) : s;
	if (s == 0) { seed = 0; return; }

	/* The seed is: 0x4000 + (exponent << 8) + (s / 100^exponent) */
	while ((x / 100) > 0) { ex++; x /= 100; }
	seed = 0x4000 + (ex << 8) + x;

	/* Handle negative numbers */
	if (s < 0) seed = ~(seed-1);
}

int main() {
	int i,x; char *f;

	/* Test the GPL 'RAND' function */
	printf("RAND:\n");
	for (i=1;i<8;i++) {
		x = gpl_rand(100);
		printf("\tIteration: %02d, Modulus: %02d (0x%02x), Seed: 0x%04x [%s]\n",i,x,x,seed,
		      ((x == gpl_rand_test_results[i-1][0] && 
			seed == gpl_rand_test_results[i-1][1]) ? "PASS" : "FAIL"));
	}
	
	/* Reset seed */
	seed = 0x3567;

	/* Test TI Basic RND function */
	printf("\nBasic RND():\n");
	for (i=1;i<11;i++) {
		f = rnd();
		printf("\tIteration: %02d, Number: %s [%s]\n",i,f,
			((!strncmp(f,rnd_test_results[i-1],strlen(rnd_test_results[i-1]))) ? "PASS" : "FAIL"));
		free(f);
	}

	/* Test TI Basic RANDOMIZE function */
	printf("\nBasic RANDOMIZE():\n");
	for (i=1;i<15;i++) {
		randomize(randomize_test_results[i-1][0]);
		printf("\tIteration: %02d, Number: %d, Seed: 0x%04x [%s]\n",i,randomize_test_results[i-1][0],seed,
			((seed == (uint16_t)randomize_test_results[i-1][1]) ? "PASS" : "FAIL"));
	}

	return 0;
}