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Add functions min_scale(numeric) and trim_scale(numeric).

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These allow better control of trailing zeroes in numeric values.

Pavel Stehule, based on an old proposal of Marko Tiikkaja's;
review by Karl Pinc

Discussion: https://postgr.es/m/CAFj8pRDjs-navGASeF0Wk74N36YGFJ+v=Ok9_knRa7vDc-qugg@mail.gmail.com
This commit is contained in:
Tom Lane
2020-01-06 12:13:53 -05:00
parent b9c130a1fd
commit 20d6225d16
6 changed files with 285 additions and 3 deletions
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91
src/backend/utils/adt/numeric.c
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@ -3179,6 +3179,97 @@ numeric_scale(PG_FUNCTION_ARGS)
PG_RETURN_INT32(NUMERIC_DSCALE(num));
}
/*
* Calculate minimum scale for value.
*/
static int
get_min_scale(NumericVar *var)
{
int min_scale;
int last_digit_pos;
/*
* Ordinarily, the input value will be "stripped" so that the last
* NumericDigit is nonzero. But we don't want to get into an infinite
* loop if it isn't, so explicitly find the last nonzero digit.
*/
last_digit_pos = var->ndigits - 1;
while (last_digit_pos >= 0 &&
var->digits[last_digit_pos] == 0)
last_digit_pos--;
if (last_digit_pos >= 0)
{
/* compute min_scale assuming that last ndigit has no zeroes */
min_scale = (last_digit_pos - var->weight) * DEC_DIGITS;
/*
* We could get a negative result if there are no digits after the
* decimal point. In this case the min_scale must be zero.
*/
if (min_scale > 0)
{
/*
* Reduce min_scale if trailing digit(s) in last NumericDigit are
* zero.
*/
NumericDigit last_digit = var->digits[last_digit_pos];
while (last_digit % 10 == 0)
{
min_scale--;
last_digit /= 10;
}
}
else
min_scale = 0;
}
else
min_scale = 0; /* result if input is zero */
return min_scale;
}
/*
* Returns minimum scale required to represent supplied value without loss.
*/
Datum
numeric_min_scale(PG_FUNCTION_ARGS)
{
Numeric num = PG_GETARG_NUMERIC(0);
NumericVar arg;
int min_scale;
if (NUMERIC_IS_NAN(num))
PG_RETURN_NULL();
init_var_from_num(num, &arg);
min_scale = get_min_scale(&arg);
free_var(&arg);
PG_RETURN_INT32(min_scale);
}
/*
* Reduce scale of numeric value to represent supplied value without loss.
*/
Datum
numeric_trim_scale(PG_FUNCTION_ARGS)
{
Numeric num = PG_GETARG_NUMERIC(0);
Numeric res;
NumericVar result;
if (NUMERIC_IS_NAN(num))
PG_RETURN_NUMERIC(make_result(&const_nan));
init_var_from_num(num, &result);
result.dscale = get_min_scale(&result);
res = make_result(&result);
free_var(&result);
PG_RETURN_NUMERIC(res);
}
/* ----------------------------------------------------------------------