/* Check different calculations for powers of ten */
/* e.g. sometimes 'POW( 10, x )' != '1Ex'	  */

// this program is part of my 'deco-Math' project, 
 
// - WIP! -, striving for DEcimal COrrect calculations 
// (also with FP numbers acc. IEEE 754) 

// general idea and base program for this check: Morten Welinder, 'gnumeric', 
// Copyright this version (c) 2021 ... Bernhard Samtleben, Hamburg, Germany, 
// all rights reserved. 


// different compilers and options: 
// compile as: 'compiler' 'options' 'name' -o 'executeable name' **'-lm'** // reg. pow( x, y ), 
// icpx -Wall -Ofast -march=native mw_powers_10_t1_long.c -o mw_powers_10_t1_long -lm
// 	-> "clang++: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated [-Wdeprecated]"
//	-> clean execution, 
// dpcpp -Wall -Ofast -march=native mw_powers_10_t1_long.c -o mw_powers_10_t1_long -lm 
//	-> silent compile and clean execution, 
// gcc -Wall -Ofast -march=native mw_powers_10_t1_long.c -o mw_powers_10_t1_long -lm
//	-> "mw_powers_10_t1_long.c:97:7: warning: incompatible implicit declaration of built-in function ‘exp10l’"
// 	-> plenty deviations and clear fails in output, e.g. a = 0.000~ for high powers, 
// 	warning off with '__builtin_exp10l' but faults remain (less?),  
// gcc -Wall -O3 -march=native mw_powers_10_t1_long.c -o mw_powers_10_t1_long -lm
//	-> "mw_powers_10_t1_long.c:97:7: warning: incompatible implicit declaration of built-in function ‘exp10l’"
// 	-> plenty deviations and clear fails in output, e.g. a = 0.000~ for high powers, 
// 	warning off with '__builtin_exp10l' but faults remain (less?),  
// gcc -O0 - faults and 'silent crash' at ~ i=70
// g++ - similar / identic? to gcc, 


#include <math.h>	// reg. e. g. 'pow( x, y )', 
#include <stdlib.h>	// reg. e. g. 'atof( s )', 
#include <stdio.h>	// reg. e. g. 'printf( s )', 

static void
compare_ab (const char *a, const char *b)
{
	if( a[ 0 ] != '0' || b[ 0 ] != '0' ) {
			printf ("a = %s\n", a);
		int a_above = (a[0] == '1');
		int b_above = (b[0] == '1');
  
		a += a_above;
		b += b_above;

		int j = 0;
		while (*a && *b) {
			int da = a_above ? (*a - '0') : ('9' - *a);
			int db = b_above ? (*b - '0') : ('9' - *b);
			if (da != db) {
//      			printf ("  da %.d \n  db %.d \n", da, db);
				if (a[1] == 0 && b[1] == 0)
					printf ("Midpoint\n");
				else if (da < db)
					printf ("a is best after %d digits\n", j);
				else
					printf ("b is best after %d digits\n", j);
				return;
			}
			a++;
			b++;
			j++;
		}
	}else{
			printf ("a = %s\n", a);
		int j = 0;
		while( ( a[ j ] == '0' && b [ j ] == '0' ) || ( a[ j ] == '.' && b [ j ] == '.' ) ) 
			j++; 
//		printf ("string identic for %d digits\n", j);

		int a_above = ( a[ j ] == '1');
		int b_above = ( b[ j ] == '1'); 
//		printf ("a[ j ] %c \n", a[ j ] ); 
//		printf ("b[ j ] %c \n", b[ j ] );

//		printf ("a_above %d b_above %d \n", a_above, b_above );
  
//		printf ("a %s \nb %s \n", a, b );

		j++; 

		while( a[ j ] && b[ j ] ) {
// is the comparison 'clean' for the last digit? 
			int da = a_above ? ( a[ j ] - '0') : ('9' - a[ j ]);
			int db = b_above ? ( b[ j ] - '0') : ('9' - b[ j ]);
//			printf ("  da %.d \n  db %.d \nj %.d \n", da, db, j);
//			printf ("a[ j ] %c \n", a[ j ] );
//			printf ("b[ j ] %c \n", b[ j ] );
//			int db = b_above ? (*b - '0') : ('9' - *b);
			if (da != db) { 
//				printf ("  da %.d \n  db %.d \nj %.d \n", da, db, j);
//				printf ("  a[ j ] %.c \n  b[ j ] %.c \n", a[ j ], b[ j ] );
				if ( da < db )
					printf ("a is best after %d digits\n", j);
				else
					printf ("b is best after %d digits\n", j);
			return;
			}
//		a++;
//    		b++;
		j++;
		}
	printf ("Midpoint\n");
	printf ("How did we get here?\n");
	}
}


int
main (int argc, char **argv)
{
//			printf ("working ... \n");
	int i;					// running counter 'cases', 
	for (i = -4952; i < 4933; i++) {	// range to check, 
//	for (i = 302; i < 330; i++) {		// range to check, reduced against too much output, 
//	for (i = -50; i < 50; i++) {		// range to check, reduced against too much output, 
//	for (i = 4932; i < 4933; i++) {		// range to check, reduced against too much output, 
		long double a, b;		// working variables
		char btxt[5000], atxt[5000];	// arrays, 

//		a = __builtin_exp10l( i );	// pow, other function, no warning from gcc, 
		a = exp10l( i );		// pow, other function, this 'clean' with icpx, 
//		a = __builtin_pow10l( i );	// 'undefined reference', 
//		a = pow10l( i );		// 'not declared', 
//		a = __builtin_powil( 10L, i );	// pow, other function, 'gcc', 
//		a = powl( 10L, i );		// pow, 
		sprintf (btxt, "1e%d", i);	// scientific string, 
		b = strtold( btxt, NULL );	// value of scientific string, seems not needing 'L' suffix, 
		printf ("    i = %d  btxt = %s\n", i, btxt);

//			printf ("a = %.5000Lf\n", a );
//			printf ("b = %.5000Lf\n", b );
		if (a != b) {
			printf ("    i = %d\n  a = %.350Lf\n  b = %.350Lf\n", i, a, b);
			printf ("btxt = %s\n", btxt);
			sprintf (atxt, "%.4990Lf", a);
			sprintf (btxt, "%.4990Lf", b);
			compare_ab (atxt, btxt);
			printf ("\n");
		}
	}
}