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[Patch, libfortran] PR 48488 Fix comments
- From: Janne Blomqvist <blomqvist dot janne at gmail dot com>
- To: Fortran List <fortran at gcc dot gnu dot org>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Fri, 29 Apr 2011 19:07:23 +0300
- Subject: [Patch, libfortran] PR 48488 Fix comments
Hi all,
now that we fixed real output, I update the comments per the patch
below and committed.
Index: io/write.c
===================================================================
--- io/write.c (revision 173168)
+++ io/write.c (working copy)
@@ -1456,10 +1456,18 @@ set_fnode_default (st_parameter_dt *dtp,
break;
}
}
-/* Output a real number with default format.
- This is 1PG14.7E2 for REAL(4), 1PG23.15E3 for REAL(8),
- 1PG28.19E4 for REAL(10) and 1PG43.34E4 for REAL(16). */
-// FX -- FIXME: should we change the default format for __float128-real(16)?
+
+/* Output a real number with default format. To guarantee that a
+ binary -> decimal -> binary roundtrip conversion recovers the
+ original value, IEEE 754-2008 requires 9, 17, 21 and 36 significant
+ digits for REAL kinds 4, 8, 10, and 16, respectively. Thus, we use
+ 1PG16.9E2 for REAL(4), 1PG25.17E3 for REAL(8), 1PG30.21E4 for
+ REAL(10) and 1PG45.36E4 for REAL(16). The exception is that the
+ Fortran standard requires outputting an extra digit when the scale
+ factor is 1 and when the magnitude of the value is such that E
+ editing is used. However, gfortran compensates for this, and thus
+ for list formatted the same number of significant digits is
+ generated both when using F and E editing. */
void
write_real (st_parameter_dt *dtp, const char *source, int length)
@@ -1472,6 +1480,8 @@ write_real (st_parameter_dt *dtp, const
dtp->u.p.scale_factor = org_scale;
}
+/* Similar to list formatted REAL output, for kPG0 where k > 0 we
+ compensate for the extra digit. */
void
write_real_g0 (st_parameter_dt *dtp, const char *source, int length, int d)
--
Janne Blomqvist