Re-implement division for numeric values using the traditional "schoolbook"

algorithm.  This is a good deal slower than our old roundoff-error-prone
code for long inputs, so we keep the old code for use in the transcendental
functions, where everything is approximate anyway.  Also create a
user-accessible function div(numeric, numeric) to provide access to the
exact result of trunc(x/y) --- since the regular numeric / operator will
round off its result, simply computing that expression in SQL doesn't
reliably give the desired answer.  This fixes bug #3387 and various related
corner cases, and improves the usefulness of PG for high-precision integer
arithmetic.

2 files changed, 99 insertions, 0 deletions

diff --git a/src/test/regress/expected/numeric.out b/src/test/regress/expected/numeric.out
index 7840990bf7d..1c5047455e8 100644
--- a/src/test/regress/expected/numeric.out
+++ b/src/test/regress/expected/numeric.out
@@ -1260,3 +1260,84 @@ SELECT * FROM num_input_test;
  -555.50
 (5 rows)
 
+--
+-- Test some corner cases for division
+--
+select 999999999999999999999::numeric/1000000000000000000000;
+        ?column?        
+------------------------
+ 1.00000000000000000000
+(1 row)
+
+select div(999999999999999999999::numeric,1000000000000000000000);
+ div 
+-----
+   0
+(1 row)
+
+select mod(999999999999999999999::numeric,1000000000000000000000);
+          mod          
+-----------------------
+ 999999999999999999999
+(1 row)
+
+select div(-9999999999999999999999::numeric,1000000000000000000000);
+ div 
+-----
+  -9
+(1 row)
+
+select mod(-9999999999999999999999::numeric,1000000000000000000000);
+          mod           
+------------------------
+ -999999999999999999999
+(1 row)
+
+select div(-9999999999999999999999::numeric,1000000000000000000000)*1000000000000000000000 + mod(-9999999999999999999999::numeric,1000000000000000000000);
+        ?column?         
+-------------------------
+ -9999999999999999999999
+(1 row)
+
+select mod (70.0,70) ;
+ mod 
+-----
+ 0.0
+(1 row)
+
+select div (70.0,70) ;
+ div 
+-----
+   1
+(1 row)
+
+select 70.0 / 70 ;
+        ?column?        
+------------------------
+ 1.00000000000000000000
+(1 row)
+
+select 12345678901234567890 % 123;
+ ?column? 
+----------
+       78
+(1 row)
+
+select 12345678901234567890 / 123;
+      ?column?      
+--------------------
+ 100371373180768845
+(1 row)
+
+select div(12345678901234567890, 123);
+        div         
+--------------------
+ 100371373180768844
+(1 row)
+
+select div(12345678901234567890, 123) * 123 + 12345678901234567890 % 123;
+       ?column?       
+----------------------
+ 12345678901234567890
+(1 row)
+
diff --git a/src/test/regress/sql/numeric.sql b/src/test/regress/sql/numeric.sql
index dc1452f9ef0..9fd6bba31ee 100644
--- a/src/test/regress/sql/numeric.sql
+++ b/src/test/regress/sql/numeric.sql
@@ -805,3 +805,21 @@ INSERT INTO num_input_test(n1) VALUES ('');
 INSERT INTO num_input_test(n1) VALUES (' N aN ');
 
 SELECT * FROM num_input_test;
+
+--
+-- Test some corner cases for division
+--
+
+select 999999999999999999999::numeric/1000000000000000000000;
+select div(999999999999999999999::numeric,1000000000000000000000);
+select mod(999999999999999999999::numeric,1000000000000000000000);
+select div(-9999999999999999999999::numeric,1000000000000000000000);
+select mod(-9999999999999999999999::numeric,1000000000000000000000);
+select div(-9999999999999999999999::numeric,1000000000000000000000)*1000000000000000000000 + mod(-9999999999999999999999::numeric,1000000000000000000000);
+select mod (70.0,70) ;
+select div (70.0,70) ;
+select 70.0 / 70 ;
+select 12345678901234567890 % 123;
+select 12345678901234567890 / 123;
+select div(12345678901234567890, 123);
+select div(12345678901234567890, 123) * 123 + 12345678901234567890 % 123;