contrib/orafce/generate_hash.c

#include <stdio.h>
#include <string.h>
#include <limits.h>

static char *days[] = {"sunday", "monday", "tuesday", "wednesday", "thursday", "friday", "saturday"};


static char *
num2day(int i)
{
	if (i > 6) return "";
	return days[i];
}

#include "tdhfunc.c"

int
main(void)
{
	int i;
	int hashes[7];

	for (i = 0; i < 7; i++)
	{
		hashes[i] = tdhfunc(days[i]);
	}

	for (i = 7; i < INT_MAX; i++)
	{
		int j;
		int collide = 0;

		for (j = 0; j < 7; j++)
		{
			int k;

			int h = hashes[j] % i;
			//printf("h(%i) = %i\n",j,h);

			for (k = 0; k < 7; k++)
			{
				if (j == k) continue;
				if (h == (hashes[k] % i))
				{
					//printf("collide on %i = %i\n", j, k);
					collide = 1;
					break;
				}
			}
			if (collide)
				break;
		}

		if (!collide)
		{
			int m = 0;
			int table[i];
			
			memset(table, -1, i * sizeof(int));

			for (m = 0; m < 7; m++)
			{
				table[hashes[m] % i] = m;
			}

			printf("/* generated by %s. This makes tdhfunc() a perfect hash. */\n", __FILE__);
			printf("typedef struct daybucket\n"
				   "{\n"
				   "	int8 dow; /* the day of the week, starting at zero for Sunday */\n"
				   "	uint8 daylen; /* length of the field below, cached */\n"
				   "	char *day; /* the day name */\n"
				   "} daybucket;\n");
			printf("#define TDH_SIZE %i\n", i);
			printf("static const daybucket TDH[TDH_SIZE] = {");

			for (m = 0; m < i; m++)
			{
				if (m)
					printf(", ");
				if (m && m % 2 == 0)
					printf("\n\t\t");
			

				printf("{%i, ", table[m]);

				if (table[m] >= 0)
				{
					char *s = num2day(table[m]);

					printf("%u, \"%s\"}", (unsigned int)strlen(s), s);
				}
				else
					printf("0, \"\"}");

				}
			printf("};\n\n");
			break;
		}
	}

	return 0;
}