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Date: Thu, 22 Dec 2022 12:41:24 -0500
From: Eric Radman <ericshane@eradman.com>
To: Dag Lem <dag@nimrod.no>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: [PATCH] Add function to_oct
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On Thu, Dec 22, 2022 at 10:08:17AM +0000, Dag Lem wrote:
> 
> The calculation of quotient and remainder can be replaced by less costly masking and shifting.
> 
> Defining
> 
> #define OCT_DIGIT_BITS 3
> #define OCT_DIGIT_BITMASK 0x7
> 
> the content of the loop can be replaced by
> 
> 		*--ptr = digits[value & OCT_DIGIT_BITMASK];
> 		value >>= OCT_DIGIT_BITS;
> 
> Also, the check for ptr > buf in the while loop can be removed. The
> check is superfluous, since buf cannot possibly be exhausted by a 32
> bit integer (the maximum octal number being 37777777777).

I integrated these suggestions in the attached -v2 patch and tested
range of values manually.

Also picked an OID > 8000 as suggested by unused_oids.

..Eric

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diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 1f63dc6dba..b539e0dc0b 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -3699,6 +3699,23 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
        </para></entry>
       </row>
 
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>to_oct</primary>
+        </indexterm>
+        <function>to_oct</function> ( <type>integer</type> )
+        <returnvalue>text</returnvalue>
+       </para>
+       <para>
+        Converts the number to its equivalent octal representation.
+       </para>
+       <para>
+        <literal>to_oct(32)</literal>
+        <returnvalue>40</returnvalue>
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 1c52deec55..586693ad8f 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -5229,6 +5229,32 @@ to_hex64(PG_FUNCTION_ARGS)
 	PG_RETURN_TEXT_P(cstring_to_text(ptr));
 }
 
+#define OCT_DIGIT_BITS 3
+#define OCT_DIGIT_BITMASK 0x7
+/*
+ * Convert an int32 to a string containing a base 8 (oct) representation of
+ * the number.
+ */
+Datum
+to_oct32(PG_FUNCTION_ARGS)
+{
+	uint32		value = (uint32) PG_GETARG_INT32(0);
+	char	    *ptr;
+	const char *digits = "01234567";
+	char		buf[32];		/* bigger than needed, but reasonable */
+
+	ptr = buf + sizeof(buf) - 1;
+	*ptr = '\0';
+
+	do
+	{
+		*--ptr = digits[value & OCT_DIGIT_BITMASK];
+		value >>= OCT_DIGIT_BITS;
+	} while (value);
+
+	PG_RETURN_TEXT_P(cstring_to_text(ptr));
+}
+
 /*
  * Return the size of a datum, possibly compressed
  *
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 98d90d9338..fde0b24563 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -3687,6 +3687,9 @@
 { oid => '2090', descr => 'convert int8 number to hex',
   proname => 'to_hex', prorettype => 'text', proargtypes => 'int8',
   prosrc => 'to_hex64' },
+{ oid => '8335', descr => 'convert int4 number to oct',
+  proname => 'to_oct', prorettype => 'text', proargtypes => 'int4',
+  prosrc => 'to_oct32' },
 
 # for character set encoding support
 
diff --git a/src/test/regress/expected/strings.out b/src/test/regress/expected/strings.out
index f028c1f10f..5ebaeb4a80 100644
--- a/src/test/regress/expected/strings.out
+++ b/src/test/regress/expected/strings.out
@@ -2143,6 +2143,15 @@ select to_hex(256::bigint*256::bigint*256::bigint*256::bigint - 1) AS "ffffffff"
  ffffffff
 (1 row)
 
+--
+-- test to_oct
+--
+select to_oct(256*256*256 - 1) AS "77777777";
+ 77777777 
+----------
+ 77777777
+(1 row)
+
 --
 -- SHA-2
 --
diff --git a/src/test/regress/sql/strings.sql b/src/test/regress/sql/strings.sql
index 932f71cbca..c4c40949e7 100644
--- a/src/test/regress/sql/strings.sql
+++ b/src/test/regress/sql/strings.sql
@@ -691,6 +691,11 @@ select to_hex(256*256*256 - 1) AS "ffffff";
 
 select to_hex(256::bigint*256::bigint*256::bigint*256::bigint - 1) AS "ffffffff";
 
+--
+-- test to_oct
+--
+select to_oct(256*256*256 - 1) AS "77777777";
+
 --
 -- SHA-2
 --

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