Oracle VARNUM/NUMBER encoding in C

Just a short example C implementation of Oracle VARNUM/NUMBER type encoding, in case you could not use library functions. I didn’t found it anywhere when needed (and afterwards I found it doesn’t helps me at all due to little ‘problem’ in ora :() and Oracle documentation is pretty unclear about how-to do it.

 

typedef	struct
{
	uint8_t len;
	uint8_t exp;
	uint8_t man[20];
} VARNUM_t;

static void setVARNUM(VARNUM_t *varnum, int64_t value)
{
	int8_t digits = 0;
	uint64_t u_value = 0;

	/* init */
	memset(varnum, 0, sizeof(*varnum));
	varnum->len	= 1;	//start len

	/* check sign */
	if(value >= 0)
	{
		u_value		= value;
		varnum->exp	= trunc(log(u_value) / log(100)) + 128 + 65;
	}
	else
	{
		u_value		= value * - 1;
		varnum->exp	= trunc(log(u_value) / log(100)) + 128 + 65;
		varnum->exp	= ~varnum->exp;
	}

	/* count value digits */
	digits = trunc(log(u_value) / log(10));
	digits = ((digits / 2) + 1);

	/* mantisa */
	for(; digits >= 0 && varnum->len <= 20; digits--)
        {
                uint64_t v_tmp = 0;

                /* prevent INT overflow for too much digits */
                if(digits > 0)
		{
			uint64_t v_pow = powl(100, digits - 1);
			v_tmp = ((u_value / v_pow) / 100) % 100;
		}
		else
			v_tmp = u_value % 100;

		if(!v_tmp)
			continue;

		/* +1 for positive, subtract 101 for negative */
		v_tmp = (value < 0 ? (101 - v_tmp) : (v_tmp + 1));
                varnum->man[varnum->len - 1] = v_tmp;
		varnum->len++;
	}

	/* terminator byte for negative value */
	if(value < 0 && varnum->len <= 20) 	{
                varnum->man[varnum->len - 1] = 102;
		varnum->len++;
	}
	return;
}

NUMBER is just the same as VARNUM but without len member, thus is one byte shorter.

Note: this is just a quick implementation that works, there are some easy optimizations possible…

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