Float output formatting options - Mailing list pgsql-hackers

Hi All,

This relates to the recent discussion about floating point output format.

The discussion was at a point where one parameter would be added to
specify the number of extra digits used in fp output formatting.
The parameter would have a 0 default value, a maximum of 2 and the
minimum remained open for discussion.

In a previous message I proposed that for double precision numbers a
minimum value of -13 would be usefful. For single precision numbers this
corresponds to a value of -4.

I downloaded the PG sources and added two parameters (as PGC_USERSET):

int extra_float4_digits, default 0, min -4, max 2
int extra_float8_digits, defualt 0, min -13, max 2

Compiled and tested for these functionalities. It is ok.

The afected files are:

src/backend/utils/adt/float.c
src/backend/utils/misc/guc.c
src/bin/psql/tab-complete.c
src/backend/utils/misc/postgresql.conf.sample

I used sources from Debian source package, postgresql_7.2.1-2woody2.

Diff's produced with diff -u are enclosed as attachments.
Can you comment on this (particularly the min values) ?
Also, if we concluded that there is a need of 2 more digits, should'nt
this be the default ?

Best regards,
Pedro M. Ferreira
--
----------------------------------------------------------------------
Pedro Miguel Frazao Fernandes Ferreira
Universidade do Algarve
Faculdade de Ciencias e Tecnologia
Campus de Gambelas
8000-117 Faro
Portugal
Tel./Fax:  (+351) 289 800950 / 289 819403
http://w3.ualg.pt/~pfrazao
--- old/postgresql-7.2.1/src/backend/utils/adt/float.c  Tue Dec 11 02:02:12 2001
+++ postgresql-7.2.1/src/backend/utils/adt/float.c      Mon Nov  4 10:32:33 2002
@@ -65,6 +65,12 @@
 #include "utils/array.h"
 #include "utils/builtins.h"

+/*
+ *     Configuration options for float4 and float8 extra digits in output format
+ */
+
+int extra_float4_digits;
+int extra_float8_digits;

 #if !(NeXT && NX_CURRENT_COMPILER_RELEASE > NX_COMPILER_RELEASE_3_2)
  /* NS3.3 has conflicting declarations of these in <math.h> */
@@ -237,7 +243,7 @@
        if (infflag < 0)
                PG_RETURN_CSTRING(strcpy(ascii, "-Infinity"));

-       sprintf(ascii, "%.*g", FLT_DIG, num);
+       sprintf(ascii, "%.*g", FLT_DIG+extra_float4_digits, num);
        PG_RETURN_CSTRING(ascii);
 }

@@ -299,7 +305,7 @@
        if (infflag < 0)
                PG_RETURN_CSTRING(strcpy(ascii, "-Infinity"));

-       sprintf(ascii, "%.*g", DBL_DIG, num);
+       sprintf(ascii, "%.*g", DBL_DIG+extra_float8_digits, num);
        PG_RETURN_CSTRING(ascii);
 }

--- old/postgresql-7.2.1/src/backend/utils/misc/guc.c   Tue Oct 30 05:38:56 2001
+++ postgresql-7.2.1/src/backend/utils/misc/guc.c       Mon Nov  4 10:53:15 2002
@@ -49,6 +49,11 @@
 extern int     CommitSiblings;
 extern bool FixBTree;

+/* For float4 and float8 extra digits in output format */
+
+extern int extra_float4_digits;
+extern int extra_float8_digits;
+
 #ifdef ENABLE_SYSLOG
 extern char *Syslog_facility;
 extern char *Syslog_ident;
@@ -502,6 +507,19 @@
                "commit_siblings", PGC_USERSET, &CommitSiblings,
                5, 1, 1000, NULL, NULL
        },
+
+       /*
+        * For float4 and float8 extra digits in output format
+        */
+       {
+               "float4_extra_digits", PGC_USERSET, &extra_float4_digits,
+               0, -4, 2, NULL, NULL
+       },
+
+       {
+               "float8_extra_digits", PGC_USERSET, &extra_float8_digits,
+               0, -13, 2, NULL, NULL
+       },

        {
                NULL, 0, NULL, 0, 0, 0, NULL, NULL
--- old/postgresql-7.2.1/src/bin/psql/tab-complete.c    Mon Nov  5 17:46:31 2001
+++ postgresql-7.2.1/src/bin/psql/tab-complete.c        Mon Nov  4 11:16:01 2002
@@ -266,6 +266,9 @@

                "default_transaction_isolation",

+               "float4_extra_digits",
+               "float8_extra_digits",
+
                NULL
        };

--- old/postgresql-7.2.1/src/backend/utils/misc/postgresql.conf.sample  Fri Jan  4 05:50:25 2002
+++ postgresql-7.2.1/src/backend/utils/misc/postgresql.conf.sample      Mon Nov  4 11:02:04 2002
@@ -182,3 +182,9 @@
 #password_encryption = false
 #sql_inheritance = true
 #transform_null_equals = false
+
+#
+# floating point extra digits in output formatting
+#
+#extra_float4_digits = 0       #min -4, max 2
+#extra_float8_digits = 0       #min -13, max 2