Harden rational edge cases and bound intermediate searches

Makefile

@@ -1,6 +1,6 @@
 MODULES = pg_rational
 EXTENSION = pg_rational
-DATA = pg_rational--0.0.1.sql pg_rational--0.0.1--0.0.2.sql pg_rational--0.0.2.sql pg_rational--0.0.2--0.0.3.sql pg_rational--0.0.3.sql
+DATA = pg_rational--0.0.1.sql pg_rational--0.0.1--0.0.2.sql pg_rational--0.0.2.sql pg_rational--0.0.2--0.0.3.sql pg_rational--0.0.3.sql pg_rational--0.0.3--0.0.4.sql pg_rational--0.0.4.sql
 REGRESS = pg_rational_test
 PG_CPPFLAGS = -std=c11 -Wextra -Wpedantic
 

README.md

@@ -13,7 +13,7 @@ precision in the denominator.
 * Defers GCD calculation until requested or absolutely required
 * Supports btree and hash indices
 * Implements Stern-Brocot trees for finding intermediate points
-* Coercion from integer/bigint/tuple
+* Coercion from integer/float/tuple
 * Custom aggregate
 
 ### Motivation
@@ -120,7 +120,7 @@ select * from todos order by prio asc;
 */
 ```
 
-This extension uses Stern-Brocot trees to find efficient intermediate points as fractions in lowest terms. It can continue to split deeper between fractions as much as any practical application requires.
+This extension uses Stern-Brocot trees to find efficient intermediate points as fractions in lowest terms. The two-argument form limits the search to one million steps; use the three-argument form to choose a different positive limit when needed.
 
 Using floats, on the other hand, and picking the midpoints between adjacent values runs out of space rapidly (you only need 50-odd inserts at the wrong spot to start hitting problems).
 
@@ -141,7 +141,7 @@ create extension pg_rational;
 
 ### Caveats
 
-The `rational_intermediate` function is super fast on typical intervals, but the narrower the range between arguments the longer it takes. We may want to add a max search depth parameter to prevent malicious values from hogging the server.
+The `rational_intermediate` function is super fast on typical intervals, but the narrower the range between arguments the longer it takes. The optional third argument sets the maximum search depth and prevents unusually narrow intervals from using the server indefinitely.
 
 ### Thanks
 

expected/pg_rational_test.out

@@ -108,6 +108,10 @@ select 2147483647.1::float::rational;
 ERROR:  value too large for rational
 select 'NAN'::float::rational;
 ERROR:  value too large for rational
+select 'Infinity'::float::rational;
+ERROR:  value too large for rational
+select '-Infinity'::float::rational;
+ERROR:  value too large for rational
 -- to float
 select '1/2'::rational::float;
  float8 
@@ -207,6 +211,20 @@ select rational_simplify('1/-2147483648');
  1/-2147483648
 (1 row)
 
+-- minimum numerator with a negative unit denominator remains representable
+select rational_simplify(rational_create(-2147483648, -1));
+ rational_simplify 
+-------------------
+ -2147483648/-1
+(1 row)
+
+-- zero with the minimum denominator has the same hash as zero over one
+select rational_hash(rational_create(0, -2147483648)) = rational_hash('0/1'::rational);
+ ?column? 
+----------
+ t
+(1 row)
+
 -- biggest value reduces
 select rational_simplify('2147483647/2147483647');
  rational_simplify 
@@ -305,6 +323,11 @@ select '2/3'::rational / '2/3';
  6/6
 (1 row)
 
+-- division by zero
+
+select '1/2'::rational / 0;
+ERROR:  division by zero
+
 -- negation
 -- flips sign of numerator
 select -('1/2'::rational);
@@ -461,6 +484,26 @@ select '1/2147483647'::rational < '2/2147483647';
  t
 (1 row)
 
+-- negative denominators created through the constructor compare by value
+
+select rational_create(1, -2) = '-1/2'::rational;
+ ?column? 
+----------
+ t
+(1 row)
+
+select rational_create(1, -2) < 0;
+ ?column? 
+----------
+ t
+(1 row)
+
+select rational_create(1, -2) > '-1/1'::rational;
+ ?column? 
+----------
+ t
+(1 row)
+
 -- lte
 select r
   from unnest(ARRAY[
@@ -688,3 +731,25 @@ select rational_intermediate(NULL, '15/16');
  1/2
 (1 row)
 
+-- bounded intermediate search
+
+select rational_intermediate(0, '1/2147483647', 1);
+ERROR:  maximum search depth exceeded
+
+select rational_intermediate(
+    '1836311903/1134903170',
+    '1134903170/701408733',
+    100
+);
+ERROR:  intermediate value overflow in rational intermediate
+
+-- bounded intermediate search is parallel safe
+
+select proparallel
+  from pg_proc
+ where proname = 'rational_intermediate'
+   and pronargs = 3;
+ proparallel 
+-------------
+ s
+(1 row)

pg_rational--0.0.3--0.0.4.sql

@@ -0,0 +1,16 @@
+CREATE FUNCTION rational_intermediate(rational, rational, integer)
+RETURNS rational
+AS '$libdir/pg_rational'
+LANGUAGE C IMMUTABLE;
+
+DO LANGUAGE plpgsql $$
+BEGIN
+	IF current_setting('server_version_num')::int >= 90600
+	THEN
+		EXECUTE $alter$
+			ALTER FUNCTION rational_intermediate(rational, rational) PARALLEL SAFE;
+			ALTER FUNCTION rational_intermediate(rational, rational, integer) PARALLEL SAFE;
+		$alter$;
+	END IF;
+END
+$$;