int rscale, bool round);
static void div_var_fast(const NumericVar *var1, const NumericVar *var2,
NumericVar *result, int rscale, bool round);
+static void div_var_int(const NumericVar *var, int ival, int ival_weight,
+ NumericVar *result, int rscale, bool round);
static int select_div_scale(const NumericVar *var1, const NumericVar *var2);
static void mod_var(const NumericVar *var1, const NumericVar *var2,
NumericVar *result);
errmsg("division by zero")));
/*
- * Now result zero check
+ * If the divisor has just one or two digits, delegate to div_var_int(),
+ * which uses fast short division.
*/
+ if (var2ndigits <= 2)
+ {
+ int idivisor;
+ int idivisor_weight;
+
+ idivisor = var2->digits[0];
+ idivisor_weight = var2->weight;
+ if (var2ndigits == 2)
+ {
+ idivisor = idivisor * NBASE + var2->digits[1];
+ idivisor_weight--;
+ }
+ if (var2->sign == NUMERIC_NEG)
+ idivisor = -idivisor;
+
+ div_var_int(var1, idivisor, idivisor_weight, result, rscale, round);
+ return;
+ }
+
+ /*
+ * Otherwise, perform full long division.
+ */
+
+ /* Result zero check */
if (var1ndigits == 0)
{
zero_var(result);
alloc_var(result, res_ndigits);
res_digits = result->digits;
- if (var2ndigits == 1)
- {
- /*
- * If there's only a single divisor digit, we can use a fast path (cf.
- * Knuth section 4.3.1 exercise 16).
- */
- divisor1 = divisor[1];
- carry = 0;
- for (i = 0; i < res_ndigits; i++)
- {
- carry = carry * NBASE + dividend[i + 1];
- res_digits[i] = carry / divisor1;
- carry = carry % divisor1;
- }
- }
- else
- {
/*
* The full multiple-place algorithm is taken from Knuth volume 2,
* Algorithm 4.3.1D.
/* And we're done with this quotient digit */
res_digits[j] = qhat;
}
- }
pfree(dividend);
errmsg("division by zero")));
/*
- * Now result zero check
+ * If the divisor has just one or two digits, delegate to div_var_int(),
+ * which uses fast short division.
*/
+ if (var2ndigits <= 2)
+ {
+ int idivisor;
+ int idivisor_weight;
+
+ idivisor = var2->digits[0];
+ idivisor_weight = var2->weight;
+ if (var2ndigits == 2)
+ {
+ idivisor = idivisor * NBASE + var2->digits[1];
+ idivisor_weight--;
+ }
+ if (var2->sign == NUMERIC_NEG)
+ idivisor = -idivisor;
+
+ div_var_int(var1, idivisor, idivisor_weight, result, rscale, round);
+ return;
+ }
+
+ /*
+ * Otherwise, perform full long division.
+ */
+
+ /* Result zero check */
if (var1ndigits == 0)
{
zero_var(result);
}
+/*
+ * div_var_int() -
+ *
+ * Divide a numeric variable by a 32-bit integer with the specified weight.
+ * The quotient var / (ival * NBASE^ival_weight) is stored in result.
+ */
+static void
+div_var_int(const NumericVar *var, int ival, int ival_weight,
+ NumericVar *result, int rscale, bool round)
+{
+ NumericDigit *var_digits = var->digits;
+ int var_ndigits = var->ndigits;
+ int res_sign;
+ int res_weight;
+ int res_ndigits;
+ NumericDigit *res_buf;
+ NumericDigit *res_digits;
+ uint32 divisor;
+ int i;
+
+ /* Guard against division by zero */
+ if (ival == 0)
+ ereport(ERROR,
+ errcode(ERRCODE_DIVISION_BY_ZERO),
+ errmsg("division by zero"));
+
+ /* Result zero check */
+ if (var_ndigits == 0)
+ {
+ zero_var(result);
+ result->dscale = rscale;
+ return;
+ }
+
+ /*
+ * Determine the result sign, weight and number of digits to calculate.
+ * The weight figured here is correct if the emitted quotient has no
+ * leading zero digits; otherwise strip_var() will fix things up.
+ */
+ if (var->sign == NUMERIC_POS)
+ res_sign = ival > 0 ? NUMERIC_POS : NUMERIC_NEG;
+ else
+ res_sign = ival > 0 ? NUMERIC_NEG : NUMERIC_POS;
+ res_weight = var->weight - ival_weight;
+ /* The number of accurate result digits we need to produce: */
+ res_ndigits = res_weight + 1 + (rscale + DEC_DIGITS - 1) / DEC_DIGITS;
+ /* ... but always at least 1 */
+ res_ndigits = Max(res_ndigits, 1);
+ /* If rounding needed, figure one more digit to ensure correct result */
+ if (round)
+ res_ndigits++;
+
+ res_buf = digitbuf_alloc(res_ndigits + 1);
+ res_buf[0] = 0; /* spare digit for later rounding */
+ res_digits = res_buf + 1;
+
+ /*
+ * Now compute the quotient digits. This is the short division algorithm
+ * described in Knuth volume 2, section 4.3.1 exercise 16, except that we
+ * allow the divisor to exceed the internal base.
+ *
+ * In this algorithm, the carry from one digit to the next is at most
+ * divisor - 1. Therefore, while processing the next digit, carry may
+ * become as large as divisor * NBASE - 1, and so it requires a 64-bit
+ * integer if this exceeds UINT_MAX.
+ */
+ divisor = Abs(ival);
+
+ if (divisor <= UINT_MAX / NBASE)
+ {
+ /* carry cannot overflow 32 bits */
+ uint32 carry = 0;
+
+ for (i = 0; i < res_ndigits; i++)
+ {
+ carry = carry * NBASE + (i < var_ndigits ? var_digits[i] : 0);
+ res_digits[i] = (NumericDigit) (carry / divisor);
+ carry = carry % divisor;
+ }
+ }
+ else
+ {
+ /* carry may exceed 32 bits */
+ uint64 carry = 0;
+
+ for (i = 0; i < res_ndigits; i++)
+ {
+ carry = carry * NBASE + (i < var_ndigits ? var_digits[i] : 0);
+ res_digits[i] = (NumericDigit) (carry / divisor);
+ carry = carry % divisor;
+ }
+ }
+
+ /* Store the quotient in result */
+ digitbuf_free(result->buf);
+ result->ndigits = res_ndigits;
+ result->buf = res_buf;
+ result->digits = res_digits;
+ result->weight = res_weight;
+ result->sign = res_sign;
+
+ /* Round or truncate to target rscale (and set result->dscale) */
+ if (round)
+ round_var(result, rscale);
+ else
+ trunc_var(result, rscale);
+
+ /* Strip leading/trailing zeroes */
+ strip_var(result);
+}
+
+
/*
* Default scale selection for division
*
{
NumericVar x;
NumericVar elem;
- NumericVar ni;
+ int ni;
double val;
int dweight;
int ndiv2;
init_var(&x);
init_var(&elem);
- init_var(&ni);
set_var_from_var(arg, &x);
/*
* Reduce x to the range -0.01 <= x <= 0.01 (approximately) by dividing by
- * 2^n, to improve the convergence rate of the Taylor series.
+ * 2^ndiv2, to improve the convergence rate of the Taylor series.
+ *
+ * Note that the overflow check above ensures that Abs(x) < 6000, which
+ * means that ndiv2 <= 20 here.
*/
if (Abs(val) > 0.01)
{
- NumericVar tmp;
-
- init_var(&tmp);
- set_var_from_var(&const_two, &tmp);
-
ndiv2 = 1;
val /= 2;
{
ndiv2++;
val /= 2;
- add_var(&tmp, &tmp, &tmp);
}
local_rscale = x.dscale + ndiv2;
- div_var_fast(&x, &tmp, &x, local_rscale, true);
-
- free_var(&tmp);
+ div_var_int(&x, 1 << ndiv2, 0, &x, local_rscale, true);
}
else
ndiv2 = 0;
add_var(&const_one, &x, result);
mul_var(&x, &x, &elem, local_rscale);
- set_var_from_var(&const_two, &ni);
- div_var_fast(&elem, &ni, &elem, local_rscale, true);
+ ni = 2;
+ div_var_int(&elem, ni, 0, &elem, local_rscale, true);
while (elem.ndigits != 0)
{
add_var(result, &elem, result);
mul_var(&elem, &x, &elem, local_rscale);
- add_var(&ni, &const_one, &ni);
- div_var_fast(&elem, &ni, &elem, local_rscale, true);
+ ni++;
+ div_var_int(&elem, ni, 0, &elem, local_rscale, true);
}
/*
free_var(&x);
free_var(&elem);
- free_var(&ni);
}
{
NumericVar x;
NumericVar xx;
- NumericVar ni;
+ int ni;
NumericVar elem;
NumericVar fact;
int nsqrt;
init_var(&x);
init_var(&xx);
- init_var(&ni);
init_var(&elem);
init_var(&fact);
set_var_from_var(result, &xx);
mul_var(result, result, &x, local_rscale);
- set_var_from_var(&const_one, &ni);
+ ni = 1;
for (;;)
{
- add_var(&ni, &const_two, &ni);
+ ni += 2;
mul_var(&xx, &x, &xx, local_rscale);
- div_var_fast(&xx, &ni, &elem, local_rscale, true);
+ div_var_int(&xx, ni, 0, &elem, local_rscale, true);
if (elem.ndigits == 0)
break;
free_var(&x);
free_var(&xx);
- free_var(&ni);
free_var(&elem);
free_var(&fact);
}
projects / users / gsingh / postgres.git / commitdiff