Speed up conversion of signed integers to C strings.

A hand-coded implementation turns out to be much faster than calling
printf().  In passing, add a few more regresion tests.

Andres Freund, with assorted, mostly cosmetic changes.

Author: robertmhaas

src/backend/utils/adt/int8.c

@@ -20,6 +20,7 @@
 #include "funcapi.h"
 #include "libpq/pqformat.h"
 #include "utils/int8.h"
+#include "utils/builtins.h"
 
 
 #define MAXINT8LEN		25
@@ -157,13 +158,10 @@ Datum
 int8out(PG_FUNCTION_ARGS)
 {
 	int64		val = PG_GETARG_INT64(0);
-	char	   *result;
-	int			len;
 	char		buf[MAXINT8LEN + 1];
+	char	   *result;
 
-	if ((len = snprintf(buf, MAXINT8LEN, INT64_FORMAT, val)) < 0)
-		elog(ERROR, "could not format int8");
-
+	pg_lltoa(val, buf);
 	result = pstrdup(buf);
 	PG_RETURN_CSTRING(result);
 }

src/backend/utils/adt/numutils.c

@@ -3,8 +3,6 @@
  * numutils.c
  *	  utility functions for I/O of built-in numeric types.
  *
- *		integer:				pg_atoi, pg_itoa, pg_ltoa
- *
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
@@ -109,27 +107,118 @@ pg_atoi(char *s, int size, int c)
 }
 
 /*
- *		pg_itoa			- converts a short int to its string represention
+ * pg_itoa: converts a signed 16-bit integer to its string representation
+ *
+ * Caller must ensure that 'a' points to enough memory to hold the result
+ * (at least 7 bytes, counting a leading sign and trailing NUL).
  *
- *		Note:
- *				previously based on ~ingres/source/gutil/atoi.c
- *				now uses vendor's sprintf conversion
+ * It doesn't seem worth implementing this separately.
  */
 void
 pg_itoa(int16 i, char *a)
 {
-	sprintf(a, "%hd", (short) i);
+	pg_ltoa((int32)i, a);
+}
+
+/*
+ * pg_ltoa: converts a signed 32-bit integer to its string representation
+ *
+ * Caller must ensure that 'a' points to enough memory to hold the result
+ * (at least 12 bytes, counting a leading sign and trailing NUL).
+ */
+void
+pg_ltoa(int32 value, char *a)
+{
+	char *start = a;
+	bool neg = false;
+
+	/*
+	 * Avoid problems with the most negative integer not being representable
+	 * as a positive integer.
+	 */
+	if (value == INT32_MIN)
+	{
+		memcpy(a, "-2147483648", 12);
+		return;
+	}
+	else if (value < 0)
+	{
+		value = -value;
+		neg = true;
+	}
+
+	/* Compute the result backwards. */
+	do
+	{
+		int32 remainder;
+		int32 oldval = value;
+		value /= 10;
+		remainder = oldval - value * 10;
+		*a++ = '0' + remainder;
+	} while (value != 0);
+	if (neg)
+		*a++ = '-';
+
+	/* Add trailing NUL byte. */
+	*a-- = '\0';
+
+	/* reverse string */
+	while (start < a)
+	{
+		char swap = *start;
+		*start++ = *a;
+		*a-- = swap;
+	}
 }
 
 /*
- *		pg_ltoa			- converts a long int to its string represention
+ * pg_lltoa: convert a signed 64bit integer to its string representation
  *
- *		Note:
- *				previously based on ~ingres/source/gutil/atoi.c
- *				now uses vendor's sprintf conversion
+ * Caller must ensure that 'a' points to enough memory to hold the result
+ * (at least MAXINT8LEN+1 bytes, counting a leading sign and trailing NUL).
  */
 void
-pg_ltoa(int32 l, char *a)
+pg_lltoa(int64 value, char *a)
 {
-	sprintf(a, "%d", l);
+	char *start = a;
+	bool neg = false;
+
+	/*
+	 * Avoid problems with the most negative integer not being representable
+	 * as a positive integer.
+	 */
+	if (value == INT64_MIN)
+	{
+		memcpy(a, "-9223372036854775808", 21);
+		return;
+	}
+	else if (value < 0)
+	{
+		value = -value;
+		neg = true;
+	}
+
+	/* Build the string by computing the wanted string backwards. */
+	do
+	{
+		int64 remainder;
+		int64 oldval = value;
+		value /= 10;
+		remainder = oldval - value * 10;
+		*a++ = '0' + remainder;
+	} while (value != 0);
+
+	if (neg)
+		*a++ = '-';
+
+	/* Add trailing NUL byte. */
+	*a-- = '\0';
+
+	/* Reverse string. */
+	while (start < a)
+	{
+		char swap = *start;
+		*start++ = *a;
+		*a-- = swap;
+	}
 }

src/include/utils/builtins.h

@@ -275,6 +275,7 @@ extern Datum current_schemas(PG_FUNCTION_ARGS);
 extern int32 pg_atoi(char *s, int size, int c);
 extern void pg_itoa(int16 i, char *a);
 extern void pg_ltoa(int32 l, char *a);
+extern void pg_lltoa(int64 ll, char *a);
 
 /*
  *		Per-opclass comparison functions for new btrees.  These are

src/test/regress/expected/int2.out

@@ -242,3 +242,16 @@ SELECT '' AS five, i.f1, i.f1 / int4 '2' AS x FROM INT2_TBL i;
       | -32767 | -16383
 (5 rows)
 
+-- corner cases
+SELECT (1<<15-1)::int2::text;
+ text  
+-------
+ 16384
+(1 row)
+
+SELECT (-1<<15)::int2::text;
+  text  
+--------
+ -32768
+(1 row)
+

src/test/regress/expected/int4.out

@@ -329,3 +329,16 @@ SELECT (2 + 2) / 2 AS two;
    2
 (1 row)
 
+-- corner cases
+SELECT (1<<31-1)::int4::text;
+    text    
+------------
+ 1073741824
+(1 row)
+
+SELECT (1<<31)::int4::text;
+    text     
+-------------
+ -2147483648
+(1 row)
+

src/test/regress/expected/int8.out

@@ -802,3 +802,16 @@ SELECT * FROM generate_series('+4567890123456789'::int8, '+4567890123456799'::in
  4567890123456799
 (6 rows)
 
+-- corner cases
+SELECT (1<<63-1)::int8::text;
+    text    
+------------
+ 1073741824
+(1 row)
+
+SELECT (1<<63)::int8::text;
+    text     
+-------------
+ -2147483648
+(1 row)
+

src/test/regress/sql/int2.sql

@@ -83,3 +83,7 @@ SELECT '' AS five, i.f1, i.f1 - int4 '2' AS x FROM INT2_TBL i;
 SELECT '' AS five, i.f1, i.f1 / int2 '2' AS x FROM INT2_TBL i;
 
 SELECT '' AS five, i.f1, i.f1 / int4 '2' AS x FROM INT2_TBL i;
+
+-- corner cases
+SELECT (1<<15-1)::int2::text;
+SELECT (-1<<15)::int2::text;

src/test/regress/sql/int4.sql

@@ -123,3 +123,7 @@ SELECT 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 AS ten;
 SELECT 2 + 2 / 2 AS three;
 
 SELECT (2 + 2) / 2 AS two;
+
+-- corner cases
+SELECT (1<<31-1)::int4::text;
+SELECT (1<<31)::int4::text;

src/test/regress/sql/int8.sql

@@ -190,3 +190,7 @@ SELECT q1, q1 << 2 AS "shl", q1 >> 3 AS "shr" FROM INT8_TBL;
 SELECT * FROM generate_series('+4567890123456789'::int8, '+4567890123456799'::int8);
 SELECT * FROM generate_series('+4567890123456789'::int8, '+4567890123456799'::int8, 0);
 SELECT * FROM generate_series('+4567890123456789'::int8, '+4567890123456799'::int8, 2);
+
+-- corner cases
+SELECT (1<<63-1)::int8::text;
+SELECT (1<<63)::int8::text;