Fix loss of fractional digits for large values in cash_numeric().

Money values exceeding about 18 digits (depending on lc_monetary)
could be inaccurately converted to numeric, due to select_div_scale()
deciding it didn't need to compute any fractional digits.  Force
its hand by setting the dscale of one division input to equal the
number of fractional digits we need.

In passing, rearrange the logic to not do useless work in locales
where money values are considered integral.

Per bug #15925 from Slawomir Chodnicki.  Back-patch to all supported
branches.

Discussion: https://postgr.es/m/15925-da9953e2674bb5c8@postgresql.org

diff --git a/src/backend/utils/adt/cash.c b/src/backend/utils/adt/cash.c
index 7bbc634bd2b1e22cd522827f5f3963a3a1e30832..2e1662a2a6c0a703fd7102ce3a65280cf60914c9 100644 (file)
--- a/src/backend/utils/adt/cash.c
+++ b/src/backend/utils/adt/cash.c
@@ -1033,13 +1033,8 @@ Datum
 cash_numeric(PG_FUNCTION_ARGS)
 {
    Cash        money = PG_GETARG_CASH(0);
-   Numeric     result;
+   Datum       result;
    int         fpoint;
-   int64       scale;
-   int         i;
-   Datum       amount;
-   Datum       numeric_scale;
-   Datum       quotient;
    struct lconv *lconvert = PGLC_localeconv();
 
    /* see comments about frac_digits in cash_in() */
@@ -1047,22 +1042,45 @@ cash_numeric(PG_FUNCTION_ARGS)
    if (fpoint < 0 || fpoint > 10)
        fpoint = 2;
 
-   /* compute required scale factor */
-   scale = 1;
-   for (i = 0; i < fpoint; i++)
-       scale *= 10;
-
-   /* form the result as money / scale */
-   amount = DirectFunctionCall1(int8_numeric, Int64GetDatum(money));
-   numeric_scale = DirectFunctionCall1(int8_numeric, Int64GetDatum(scale));
-   quotient = DirectFunctionCall2(numeric_div, amount, numeric_scale);
+   /* convert the integral money value to numeric */
+   result = DirectFunctionCall1(int8_numeric, Int64GetDatum(money));
 
-   /* forcibly round to exactly the intended number of digits */
-   result = DatumGetNumeric(DirectFunctionCall2(numeric_round,
-                                                quotient,
-                                                Int32GetDatum(fpoint)));
+   /* scale appropriately, if needed */
+   if (fpoint > 0)
+   {
+       int64       scale;
+       int         i;
+       Datum       numeric_scale;
+       Datum       quotient;
+
+       /* compute required scale factor */
+       scale = 1;
+       for (i = 0; i < fpoint; i++)
+           scale *= 10;
+       numeric_scale = DirectFunctionCall1(int8_numeric,
+                                           Int64GetDatum(scale));
+
+       /*
+        * Given integral inputs approaching INT64_MAX, select_div_scale()
+        * might choose a result scale of zero, causing loss of fractional
+        * digits in the quotient.  We can ensure an exact result by setting
+        * the dscale of either input to be at least as large as the desired
+        * result scale.  numeric_round() will do that for us.
+        */
+       numeric_scale = DirectFunctionCall2(numeric_round,
+                                           numeric_scale,
+                                           Int32GetDatum(fpoint));
+
+       /* Now we can safely divide ... */
+       quotient = DirectFunctionCall2(numeric_div, result, numeric_scale);
+
+       /* ... and forcibly round to exactly the intended number of digits */
+       result = DirectFunctionCall2(numeric_round,
+                                    quotient,
+                                    Int32GetDatum(fpoint));
+   }
 
-   PG_RETURN_NUMERIC(result);
+   PG_RETURN_DATUM(result);
 }
 
 /* numeric_cash()

diff --git a/src/test/regress/expected/money.out b/src/test/regress/expected/money.out
index ab86595fc0219343da3374c11303e7d2d435d7a8..fc71a72fed319b76848db757efb4092a54cb3a8d 100644 (file)
--- a/src/test/regress/expected/money.out
+++ b/src/test/regress/expected/money.out
@@ -1,6 +1,8 @@
 --
 -- MONEY
 --
+-- Note that we assume lc_monetary has been set to C.
+--
 CREATE TABLE money_data (m money);
 INSERT INTO money_data VALUES ('123');
 SELECT * FROM money_data;
@@ -476,7 +478,7 @@ SELECT (-12345678901234567)::numeric::money;
  -$12,345,678,901,234,567.00
 (1 row)
 
--- Cast from money
+-- Cast from money to numeric
 SELECT '12345678901234567'::money::numeric;
        numeric        
 ----------------------
@@ -489,3 +491,15 @@ SELECT '-12345678901234567'::money::numeric;
  -12345678901234567.00
 (1 row)
 
+SELECT '92233720368547758.07'::money::numeric;
+       numeric        
+----------------------
+ 92233720368547758.07
+(1 row)
+
+SELECT '-92233720368547758.08'::money::numeric;
+        numeric        
+-----------------------
+ -92233720368547758.08
+(1 row)
+

diff --git a/src/test/regress/sql/money.sql b/src/test/regress/sql/money.sql
index 37b9ecce1fc4fea57bfc79d41ef99e7d80892d9a..5e746286c9079e0444c509d81e02e0359ce3e83a 100644 (file)
--- a/src/test/regress/sql/money.sql
+++ b/src/test/regress/sql/money.sql
@@ -1,6 +1,8 @@
 --
 -- MONEY
 --
+-- Note that we assume lc_monetary has been set to C.
+--
 
 CREATE TABLE money_data (m money);
 
@@ -122,6 +124,8 @@ SELECT (-1234567890)::int4::money;
 SELECT (-12345678901234567)::int8::money;
 SELECT (-12345678901234567)::numeric::money;
 
--- Cast from money
+-- Cast from money to numeric
 SELECT '12345678901234567'::money::numeric;
 SELECT '-12345678901234567'::money::numeric;
+SELECT '92233720368547758.07'::money::numeric;
+SELECT '-92233720368547758.08'::money::numeric;