From f3e3034684c7ac44a14c70d6a248d8acee303176 Mon Sep 17 00:00:00 2001

From: law <law@138bc75d-0d04-0410-961f-82ee72b054a4>

Date: Thu, 10 May 2018 11:48:34 +0100

Subject: [PATCH 01/16] Default widths for i, f and g format specifiers in

 format strings.

Enabled using -fdec.

The behaviour is modelled on the Oracle Fortran compiler. At the time

of writing, the details were available at this URL:

  https://docs.oracle.com/cd/E19957-01/805-4939/6j4m0vnc3/index.html#z4000743746d

Addition by Mark Eggleston <mark.eggleston@codethink.com>:

Use -fdec-format-defaults to enable this feature. Also enabled using -fdec.

---

 gcc/fortran/io.c                                   | 31 +++++++++++--

 gcc/fortran/lang.opt                               |  4 ++

 gcc/fortran/options.c                              |  1 +

 .../gfortran.dg/fmt_f_default_field_width_1.f90    | 43 ++++++++++++++++++

 .../gfortran.dg/fmt_f_default_field_width_2.f90    | 46 +++++++++++++++++++

 .../gfortran.dg/fmt_f_default_field_width_3.f90    | 28 ++++++++++++

 .../gfortran.dg/fmt_g_default_field_width_1.f90    | 48 ++++++++++++++++++++

 .../gfortran.dg/fmt_g_default_field_width_2.f90    | 52 ++++++++++++++++++++++

 .../gfortran.dg/fmt_g_default_field_width_3.f90    | 31 +++++++++++++

 .../gfortran.dg/fmt_i_default_field_width_1.f90    | 38 ++++++++++++++++

 .../gfortran.dg/fmt_i_default_field_width_2.f90    | 42 +++++++++++++++++

 .../gfortran.dg/fmt_i_default_field_width_3.f90    | 35 +++++++++++++++

 libgfortran/io/format.c                            | 35 +++++++++++++++

 libgfortran/io/io.h                                | 50 +++++++++++++++++++++

 libgfortran/io/read.c                              |  6 +++

 libgfortran/io/write.c                             | 22 +++++----

 libgfortran/io/write_float.def                     | 37 ++++++++++++---

 17 files changed, 531 insertions(+), 18 deletions(-)

 create mode 100644 gcc/testsuite/gfortran.dg/fmt_f_default_field_width_1.f90

 create mode 100644 gcc/testsuite/gfortran.dg/fmt_f_default_field_width_2.f90

 create mode 100644 gcc/testsuite/gfortran.dg/fmt_f_default_field_width_3.f90

 create mode 100644 gcc/testsuite/gfortran.dg/fmt_g_default_field_width_1.f90

 create mode 100644 gcc/testsuite/gfortran.dg/fmt_g_default_field_width_2.f90

 create mode 100644 gcc/testsuite/gfortran.dg/fmt_g_default_field_width_3.f90

 create mode 100644 gcc/testsuite/gfortran.dg/fmt_i_default_field_width_1.f90

 create mode 100644 gcc/testsuite/gfortran.dg/fmt_i_default_field_width_2.f90

 create mode 100644 gcc/testsuite/gfortran.dg/fmt_i_default_field_width_3.f90

diff --git a/gcc/fortran/io.c b/gcc/fortran/io.c

index 9828897852a..57117579627 100644

--- a/gcc/fortran/io.c

+++ b/gcc/fortran/io.c

@@ -903,6 +903,13 @@ data_desc:

       if (u != FMT_POSINT)

 	{

+	  if (flag_dec_format_defaults)

+	    {

+	      /* Assume a default width based on the variable size.  */

+	      saved_token = u;

+	      break;

+	    }

+

 	  format_locus.nextc += format_string_pos;

 	  gfc_error ("Positive width required in format "

 			 "specifier %s at %L", token_to_string (t),

@@ -1027,6 +1034,13 @@ data_desc:

 	goto fail;

       if (t != FMT_ZERO && t != FMT_POSINT)

 	{

+	  if (flag_dec_format_defaults)

+	    {

+	      /* Assume the default width is expected here and continue lexing.  */

+	      value = 0; /* It doesn't matter what we set the value to here.  */

+	      saved_token = t;

+	      break;

+	    }

 	  error = nonneg_required;

 	  goto syntax;

 	}

@@ -1096,8 +1110,17 @@ data_desc:

 	goto fail;

       if (t != FMT_ZERO && t != FMT_POSINT)

 	{

-	  error = nonneg_required;

-	  goto syntax;

+	  if (flag_dec_format_defaults)

+	    {

+	      /* Assume the default width is expected here and continue lexing.  */

+	      value = 0; /* It doesn't matter what we set the value to here.  */

+	      saved_token = t;

+	    }

+	  else

+	    {

+	      error = nonneg_required;

+	      goto syntax;

+	    }

 	}

       else if (is_input && t == FMT_ZERO)

 	{

@@ -4368,8 +4391,8 @@ get_io_list:

     }

   /* See if we want to use defaults for missing exponents in real transfers

-     and other DEC runtime extensions.  */

-  if (flag_dec)

+     and other DEC runtime extensions. */

+  if (flag_dec_format_defaults)

     dt->dec_ext = 1;

   /* A full IO statement has been matched.  Check the constraints.  spec_end is

diff --git a/gcc/fortran/lang.opt b/gcc/fortran/lang.opt

index 9151d02c491..26e82601b62 100644

--- a/gcc/fortran/lang.opt

+++ b/gcc/fortran/lang.opt

@@ -444,6 +444,10 @@ fdec-include

 Fortran Var(flag_dec_include)

 Enable legacy parsing of INCLUDE as statement.

+fdec-format-defaults

+Fortran Var(flag_dec_format_defaults)

+Enable default widths for i, f and g format specifiers.

+

 fdec-intrinsic-ints

 Fortran Var(flag_dec_intrinsic_ints)

 Enable kind-specific variants of integer intrinsic functions.

diff --git a/gcc/fortran/options.c b/gcc/fortran/options.c

index 02970d59066..4f91486e977 100644

--- a/gcc/fortran/options.c

+++ b/gcc/fortran/options.c

@@ -74,6 +74,7 @@ set_dec_flags (int value)

   SET_BITFLAG (flag_dec_static, value, value);

   SET_BITFLAG (flag_dec_math, value, value);

   SET_BITFLAG (flag_dec_include, value, value);

+  SET_BITFLAG (flag_dec_format_defaults, value, value);

 }

 /* Finalize DEC flags.  */

diff --git a/gcc/testsuite/gfortran.dg/fmt_f_default_field_width_1.f90 b/gcc/testsuite/gfortran.dg/fmt_f_default_field_width_1.f90

new file mode 100644

index 00000000000..49c77155761

--- /dev/null

+++ b/gcc/testsuite/gfortran.dg/fmt_f_default_field_width_1.f90

@@ -0,0 +1,43 @@

+! { dg-do run }

+! { dg-options -fdec }

+!

+! Test case for the default field widths enabled by the -fdec-format-defaults flag.

+!

+! This feature is not part of any Fortran standard, but it is supported by the

+! Oracle Fortran compiler and others.

+!

+! libgfortran uses printf() internally to implement FORMAT. If you print float

+! values to a higher precision than the type can actually store, the results

+! are implementation dependent: some platforms print zeros, others print random

+! numbers. Don't depend on this behaviour in tests because they will not be

+! portable.

+

+    character(50) :: buffer

+

+    real*4 :: real_4

+    real*8 :: real_8

+    real*16 :: real_16

+    integer :: len

+

+    real_4 = 4.18

+    write(buffer, '(A, F, A)') ':',real_4,':'

+    print *,buffer

+    if (buffer.ne.":      4.1799998:") stop 1

+

+    real_4 = 0.00000018

+    write(buffer, '(A, F, A)') ':',real_4,':'

+    print *,buffer

+    if (buffer.ne.":      0.0000002:") stop 2

+

+    real_8 = 4.18

+    write(buffer, '(A, F, A)') ':',real_8,':'

+    print *,buffer

+    len = len_trim(buffer)

+    if (len /= 27) stop 3

+

+    real_16 = 4.18

+    write(buffer, '(A, F, A)') ':',real_16,':'

+    print *,buffer

+    len = len_trim(buffer)

+    if (len /= 44) stop 4

+end

diff --git a/gcc/testsuite/gfortran.dg/fmt_f_default_field_width_2.f90 b/gcc/testsuite/gfortran.dg/fmt_f_default_field_width_2.f90

new file mode 100644

index 00000000000..1c2ec0413a7

--- /dev/null

+++ b/gcc/testsuite/gfortran.dg/fmt_f_default_field_width_2.f90

@@ -0,0 +1,46 @@

+! { dg-do run }

+! { dg-options -fdec-format-defaults }

+!

+! Test case for the default field widths enabled by the -fdec-format-defaults flag.

+!

+! This feature is not part of any Fortran standard, but it is supported by the

+! Oracle Fortran compiler and others.

+!

+! libgfortran uses printf() internally to implement FORMAT. If you print float

+! values to a higher precision than the type can actually store, the results

+! are implementation dependent: some platforms print zeros, others print random

+! numbers. Don't depend on this behaviour in tests because they will not be

+! portable.

+!

+! Test case added by Mark Eggleston <mark.eggleston@codethink.com> to check

+! use of -fdec-format-defaults

+!

+    character(50) :: buffer

+

+    real*4 :: real_4

+    real*8 :: real_8

+    real*16 :: real_16

+    integer :: len

+

+    real_4 = 4.18

+    write(buffer, '(A, F, A)') ':',real_4,':'

+    print *,buffer

+    if (buffer.ne.":      4.1799998:") stop 1

+

+    real_4 = 0.00000018

+    write(buffer, '(A, F, A)') ':',real_4,':'

+    print *,buffer

+    if (buffer.ne.":      0.0000002:") stop 2

+

+    real_8 = 4.18

+    write(buffer, '(A, F, A)') ':',real_8,':'

+    print *,buffer

+    len = len_trim(buffer)

+    if (len /= 27) stop 3

+

+    real_16 = 4.18

+    write(buffer, '(A, F, A)') ':',real_16,':'

+    print *,buffer

+    len = len_trim(buffer)

+    if (len /= 44) stop 4

+end

diff --git a/gcc/testsuite/gfortran.dg/fmt_f_default_field_width_3.f90 b/gcc/testsuite/gfortran.dg/fmt_f_default_field_width_3.f90

new file mode 100644

index 00000000000..e513063189b

--- /dev/null

+++ b/gcc/testsuite/gfortran.dg/fmt_f_default_field_width_3.f90

@@ -0,0 +1,28 @@

+! { dg-do compile }

+! { dg-options "-fdec -fno-dec-format-defaults" }

+!

+! Test case for the default field widths not enabled.

+!

+! Test case added by Mark Eggleston <mark.eggleston@codethink.com> to check

+! use of -fno-dec-format-defaults

+!

+

+    character(50) :: buffer

+

+    real*4 :: real_4

+    real*8 :: real_8

+    real*16 :: real_16

+    integer :: len

+

+    real_4 = 4.18

+    write(buffer, '(A, F, A)') ':',real_4,':' ! { dg-error "Nonnegative width required" }

+

+    real_4 = 0.00000018

+    write(buffer, '(A, F, A)') ':',real_4,':' ! { dg-error "Nonnegative width required" }

+

+    real_8 = 4.18

+    write(buffer, '(A, F, A)') ':',real_8,':' ! { dg-error "Nonnegative width required" }

+

+    real_16 = 4.18

+    write(buffer, '(A, F, A)') ':',real_16,':' ! { dg-error "Nonnegative width required" }

+end

diff --git a/gcc/testsuite/gfortran.dg/fmt_g_default_field_width_1.f90 b/gcc/testsuite/gfortran.dg/fmt_g_default_field_width_1.f90

new file mode 100644

index 00000000000..6e2ad141d4a

--- /dev/null

+++ b/gcc/testsuite/gfortran.dg/fmt_g_default_field_width_1.f90

@@ -0,0 +1,48 @@

+! { dg-do run }

+! { dg-options -fdec }

+!

+! Test case for the default field widths enabled by the -fdec-format-defaults flag.

+!

+! This feature is not part of any Fortran standard, but it is supported by the

+! Oracle Fortran compiler and others.

+!

+! libgfortran uses printf() internally to implement FORMAT. If you print float

+! values to a higher precision than the type can actually store, the results

+! are implementation dependent: some platforms print zeros, others print random

+! numbers. Don't depend on this behaviour in tests because they will not be

+! portable.

+

+    character(50) :: buffer

+

+    real*4 :: real_4

+    real*8 :: real_8

+    real*16 :: real_16

+    integer :: len

+

+    real_4 = 4.18

+    write(buffer, '(A, G, A)') ':',real_4,':'

+    print *,buffer

+    if (buffer.ne.":   4.180000    :") stop 1

+

+    real_4 = 0.00000018

+    write(buffer, '(A, G, A)') ':',real_4,':'

+    print *,buffer

+    if (buffer.ne.":  0.1800000E-06:") stop 2

+

+    real_4 = 18000000.4

+    write(buffer, '(A, G, A)') ':',real_4,':'

+    print *,buffer

+    if (buffer.ne.":  0.1800000E+08:") stop 3

+

+    real_8 = 4.18

+    write(buffer, '(A, G, A)') ':',real_8,':'

+    print *,buffer

+    len = len_trim(buffer)

+    if (len /= 27) stop 4

+

+    real_16 = 4.18

+    write(buffer, '(A, G, A)') ':',real_16,':'

+    print *,buffer

+    len = len_trim(buffer)

+    if (len /= 44) stop 5

+end

diff --git a/gcc/testsuite/gfortran.dg/fmt_g_default_field_width_2.f90 b/gcc/testsuite/gfortran.dg/fmt_g_default_field_width_2.f90

new file mode 100644

index 00000000000..7b218af8610

--- /dev/null

+++ b/gcc/testsuite/gfortran.dg/fmt_g_default_field_width_2.f90

@@ -0,0 +1,52 @@

+! { dg-do run }

+! { dg-options -fdec-format-defaults }

+!

+! Test case for the default field widths enabled by the -fdec-format-defaults flag.

+!

+! This feature is not part of any Fortran standard, but it is supported by the

+! Oracle Fortran compiler and others.

+!

+! libgfortran uses printf() internally to implement FORMAT. If you print float

+! values to a higher precision than the type can actually store, the results

+! are implementation dependent: some platforms print zeros, others print random

+! numbers. Don't depend on this behaviour in tests because they will not be

+! portable.

+!

+! Test case added by Mark Eggleston <mark.eggleston@codethink.com> to check

+! use of -fdec-format-defaults

+!

+

+    character(50) :: buffer

+

+    real*4 :: real_4

+    real*8 :: real_8

+    real*16 :: real_16

+    integer :: len

+

+    real_4 = 4.18

+    write(buffer, '(A, G, A)') ':',real_4,':'

+    print *,buffer

+    if (buffer.ne.":   4.180000    :") stop 1

+

+    real_4 = 0.00000018

+    write(buffer, '(A, G, A)') ':',real_4,':'

+    print *,buffer

+    if (buffer.ne.":  0.1800000E-06:") stop 2

+

+    real_4 = 18000000.4

+    write(buffer, '(A, G, A)') ':',real_4,':'

+    print *,buffer

+    if (buffer.ne.":  0.1800000E+08:") stop 3

+

+    real_8 = 4.18

+    write(buffer, '(A, G, A)') ':',real_8,':'

+    print *,buffer

+    len = len_trim(buffer)

+    if (len /= 27) stop 4

+

+    real_16 = 4.18

+    write(buffer, '(A, G, A)') ':',real_16,':'

+    print *,buffer

+    len = len_trim(buffer)

+    if (len /= 44) stop 5

+end

diff --git a/gcc/testsuite/gfortran.dg/fmt_g_default_field_width_3.f90 b/gcc/testsuite/gfortran.dg/fmt_g_default_field_width_3.f90

new file mode 100644

index 00000000000..e255c2f94a0

--- /dev/null

+++ b/gcc/testsuite/gfortran.dg/fmt_g_default_field_width_3.f90

@@ -0,0 +1,31 @@

+! { dg-do compile }

+! { dg-options "-fdec -fno-dec-format-defaults" }

+!

+! Test case for the default field widths not enabled.

+!

+! Test case added by Mark Eggleston <mark.eggleston@codethink.com> to check

+! use of -fno-dec-format-defaults

+!

+

+    character(50) :: buffer

+

+    real*4 :: real_4

+    real*8 :: real_8

+    real*16 :: real_16

+    integer :: len

+

+    real_4 = 4.18

+    write(buffer, '(A, G, A)') ':',real_4,':' ! { dg-error "Positive width required" }

+

+    real_4 = 0.00000018

+    write(buffer, '(A, G, A)') ':',real_4,':' ! { dg-error "Positive width required" }

+

+    real_4 = 18000000.4

+    write(buffer, '(A, G, A)') ':',real_4,':' ! { dg-error "Positive width required" }

+

+    real_8 = 4.18

+    write(buffer, '(A, G, A)') ':',real_8,':' ! { dg-error "Positive width required" }

+

+    real_16 = 4.18

+    write(buffer, '(A, G, A)') ':',real_16,':' ! { dg-error "Positive width required" }

+end

diff --git a/gcc/testsuite/gfortran.dg/fmt_i_default_field_width_1.f90 b/gcc/testsuite/gfortran.dg/fmt_i_default_field_width_1.f90

new file mode 100644

index 00000000000..0d32d240394

--- /dev/null

+++ b/gcc/testsuite/gfortran.dg/fmt_i_default_field_width_1.f90

@@ -0,0 +1,38 @@

+! { dg-do run }

+! { dg-options -fdec }

+!

+! Test case for the default field widths enabled by the -fdec-format-defaults flag.

+!

+! This feature is not part of any Fortran standard, but it is supported by the

+! Oracle Fortran compiler and others.

+

+    character(50) :: buffer

+    character(1) :: colon

+

+    integer*2 :: integer_2

+    integer*4 :: integer_4

+    integer*8 :: integer_8

+

+    write(buffer, '(A, I, A)') ':',12340,':'

+    print *,buffer

+    if (buffer.ne.":       12340:") stop 1

+

+    read(buffer, '(A1, I, A1)') colon, integer_4, colon

+    if (integer_4.ne.12340) stop 2

+

+    integer_2 = -99

+    write(buffer, '(A, I, A)') ':',integer_2,':'

+    print *,buffer

+    if (buffer.ne.":    -99:") stop 3

+

+    integer_8 = -11112222

+    write(buffer, '(A, I, A)') ':',integer_8,':'

+    print *,buffer

+    if (buffer.ne.":              -11112222:") stop 4

+

+! If the width is 7 and there are 7 leading zeroes, the result should be zero.

+    integer_2 = 789

+    buffer = '0000000789'

+    read(buffer, '(I)') integer_2

+    if (integer_2.ne.0) stop 5

+end

diff --git a/gcc/testsuite/gfortran.dg/fmt_i_default_field_width_2.f90 b/gcc/testsuite/gfortran.dg/fmt_i_default_field_width_2.f90

new file mode 100644

index 00000000000..6cee3f86809

--- /dev/null

+++ b/gcc/testsuite/gfortran.dg/fmt_i_default_field_width_2.f90

@@ -0,0 +1,42 @@

+! { dg-do run }

+! { dg-options -fdec-format-defaults }

+!

+! Test case for the default field widths enabled by the -fdec-format-defaults flag.

+!

+! This feature is not part of any Fortran standard, but it is supported by the

+! Oracle Fortran compiler and others.

+!

+! Test case added by Mark Eggleston <mark.eggleston@codethink.com> to check

+! use of -fdec-format-defaults

+!

+

+    character(50) :: buffer

+    character(1) :: colon

+

+    integer*2 :: integer_2

+    integer*4 :: integer_4

+    integer*8 :: integer_8

+

+    write(buffer, '(A, I, A)') ':',12340,':'

+    print *,buffer

+    if (buffer.ne.":       12340:") stop 1

+

+    read(buffer, '(A1, I, A1)') colon, integer_4, colon

+    if (integer_4.ne.12340) stop 2

+

+    integer_2 = -99

+    write(buffer, '(A, I, A)') ':',integer_2,':'

+    print *,buffer

+    if (buffer.ne.":    -99:") stop 3

+

+    integer_8 = -11112222

+    write(buffer, '(A, I, A)') ':',integer_8,':'

+    print *,buffer

+    if (buffer.ne.":              -11112222:") stop 4

+

+! If the width is 7 and there are 7 leading zeroes, the result should be zero.

+    integer_2 = 789

+    buffer = '0000000789'

+    read(buffer, '(I)') integer_2

+    if (integer_2.ne.0) stop 5

+end

diff --git a/gcc/testsuite/gfortran.dg/fmt_i_default_field_width_3.f90 b/gcc/testsuite/gfortran.dg/fmt_i_default_field_width_3.f90

new file mode 100644

index 00000000000..3a6684b3c4d

--- /dev/null

+++ b/gcc/testsuite/gfortran.dg/fmt_i_default_field_width_3.f90

@@ -0,0 +1,35 @@

+! { dg-do compile }

+! { dg-options "-fdec -fno-dec-format-defaults" }

+!

+! Test case for the default field widths enabled by the -fdec-format-defaults flag.

+!

+! This feature is not part of any Fortran standard, but it is supported by the

+! Oracle Fortran compiler and others.

+!

+! Test case added by Mark Eggleston <mark.eggleston@codethink.com> to check

+! use of -fdec-format-defaults

+!

+

+    character(50) :: buffer

+    character(1) :: colon

+

+    integer*2 :: integer_2

+    integer*4 :: integer_4

+    integer*8 :: integer_8

+

+    write(buffer, '(A, I, A)') ':',12340,':' ! { dg-error "Nonnegative width required" }

+

+    read(buffer, '(A1, I, A1)') colon, integer_4, colon ! { dg-error "Nonnegative width required" }

+    if (integer_4.ne.12340) stop 2

+

+    integer_2 = -99

+    write(buffer, '(A, I, A)') ':',integer_2,':' ! { dg-error "Nonnegative width required" }

+

+    integer_8 = -11112222

+    write(buffer, '(A, I, A)') ':',integer_8,':' ! { dg-error "Nonnegative width required" }

+

+! If the width is 7 and there are 7 leading zeroes, the result should be zero.

+    integer_2 = 789

+    buffer = '0000000789'

+    read(buffer, '(I)') integer_2 ! { dg-error "Nonnegative width required" }

+end

diff --git a/libgfortran/io/format.c b/libgfortran/io/format.c

index 688764785da..e798d9bda87 100644

--- a/libgfortran/io/format.c

+++ b/libgfortran/io/format.c

@@ -956,12 +956,33 @@ parse_format_list (st_parameter_dt *dtp, bool *seen_dd)

 	  *seen_dd = true;

 	  if (u != FMT_POSINT && u != FMT_ZERO)

 	    {

+	      if (dtp->common.flags & IOPARM_DT_DEC_EXT)

+		{

+		  tail->u.real.w = DEFAULT_WIDTH;

+		  tail->u.real.d = 0;

+		  tail->u.real.e = -1;

+		  fmt->saved_token = u;

+		  break;

+		}

 	      fmt->error = nonneg_required;

 	      goto finished;

 	    }

 	}

+      else if (u == FMT_ZERO)

+	{

+	  fmt->error = posint_required;

+	  goto finished;

+	}

       else if (u != FMT_POSINT)

 	{

+	  if (dtp->common.flags & IOPARM_DT_DEC_EXT)

+	    {

+	      tail->u.real.w = DEFAULT_WIDTH;

+	      tail->u.real.d = 0;

+	      tail->u.real.e = -1;

+	      fmt->saved_token = u;

+	      break;

+	    }

 	  fmt->error = posint_required;

 	  goto finished;

 	}

@@ -1100,6 +1121,13 @@ parse_format_list (st_parameter_dt *dtp, bool *seen_dd)

 	{

 	  if (t != FMT_POSINT)

 	    {

+	      if (dtp->common.flags & IOPARM_DT_DEC_EXT)

+		{

+		  tail->u.integer.w = DEFAULT_WIDTH;

+		  tail->u.integer.m = -1;

+		  fmt->saved_token = t;

+		  break;

+		}

 	      fmt->error = posint_required;

 	      goto finished;

 	    }

@@ -1108,6 +1136,13 @@ parse_format_list (st_parameter_dt *dtp, bool *seen_dd)

 	{

 	  if (t != FMT_ZERO && t != FMT_POSINT)

 	    {

+	      if (dtp->common.flags & IOPARM_DT_DEC_EXT)

+		{

+		  tail->u.integer.w = DEFAULT_WIDTH;

+		  tail->u.integer.m = -1;

+		  fmt->saved_token = t;

+		  break;

+		}

 	      fmt->error = nonneg_required;

 	      goto finished;

 	    }

diff --git a/libgfortran/io/io.h b/libgfortran/io/io.h

index 5caaea280f0..f5e63797ba1 100644

--- a/libgfortran/io/io.h

+++ b/libgfortran/io/io.h

@@ -1011,6 +1011,56 @@ memset4 (gfc_char4_t *p, gfc_char4_t c, int k)

     *p++ = c;

 }

+/* Used in width fields to indicate that the default should be used */

+#define DEFAULT_WIDTH -1

+

+/* Defaults for certain format field descriptors. These are decided based on

+ * the type of the value being formatted.

+ *

+ * The behaviour here is modelled on the Oracle Fortran compiler. At the time

+ * of writing, the details were available at this URL:

+ *

+ *   https://docs.oracle.com/cd/E19957-01/805-4939/6j4m0vnc3/index.html#z4000743746d

+ */

+

+static inline int

+default_width_for_integer (int kind)

+{

+  switch (kind)

+    {

+    case 1:

+    case 2:  return  7;

+    case 4:  return 12;

+    case 8:  return 23;

+    case 16: return 44;

+    default: return  0;

+    }

+}

+

+static inline int

+default_width_for_float (int kind)

+{

+  switch (kind)

+    {

+    case 4:  return 15;

+    case 8:  return 25;

+    case 16: return 42;

+    default: return  0;

+    }

+}

+

+static inline int

+default_precision_for_float (int kind)

+{

+  switch (kind)

+    {

+    case 4:  return 7;

+    case 8:  return 16;

+    case 16: return 33;

+    default: return 0;

+    }

+}

+

 #endif

 extern void

diff --git a/libgfortran/io/read.c b/libgfortran/io/read.c

index 52ffb4639ac..be9f6cb6f76 100644

--- a/libgfortran/io/read.c

+++ b/libgfortran/io/read.c

@@ -635,6 +635,12 @@ read_decimal (st_parameter_dt *dtp, const fnode *f, char *dest, int length)

   w = f->u.w;

+  /* This is a legacy extension, and the frontend will only allow such cases

+   * through when -fdec-format-defaults is passed.

+   */

+  if (w == DEFAULT_WIDTH)

+    w = default_width_for_integer (length);

+

   p = read_block_form (dtp, &w);

   if (p == NULL)

diff --git a/libgfortran/io/write.c b/libgfortran/io/write.c

index c8811e200e0..4ef35561fdd 100644

--- a/libgfortran/io/write.c

+++ b/libgfortran/io/write.c

@@ -685,9 +685,8 @@ write_l (st_parameter_dt *dtp, const fnode *f, char *source, int len)

   p[wlen - 1] = (n) ? 'T' : 'F';

 }

-

 static void

-write_boz (st_parameter_dt *dtp, const fnode *f, const char *q, int n)

+write_boz (st_parameter_dt *dtp, const fnode *f, const char *q, int n, int len)

 {

   int w, m, digits, nzero, nblank;

   char *p;

@@ -720,6 +719,9 @@ write_boz (st_parameter_dt *dtp, const fnode *f, const char *q, int n)

   /* Select a width if none was specified.  The idea here is to always

      print something.  */

+  if (w == DEFAULT_WIDTH)

+    w = default_width_for_integer (len);

+

   if (w == 0)

     w = ((digits < m) ? m : digits);