This file lists recent changes to the GNU Fortran compiler. Copyright (C) 1995, 1996 Free Software Foundation, Inc. You may copy, distribute, and modify it freely as long as you preserve this copyright notice and permission notice.

# News About GNU Fortran

Changes made to recent versions of GNU Fortran are listed below, with the most recent version first.

The changes are generally listed in order:

1. Code-generation and run-time-library bugs
2. Compiler and run-time-library crashes involving valid code
3. New features
4. Fixes and enhancements to existing features
5. New diagnostics
6. Internal improvements
7. Miscellany

This order is not strict---for example, some items involve a combination of these elements.

## In 0.5.22:

- Fix code generation for iterative `DO` loops that have one or more references to the iteration variable, or to aliases of it, in their control expressions. For example, `DO 10 J=2,J` now is compiled correctly.
- Fix a code-generation bug that afflicted Intel x86 targets when `-O2` was specified compiling, for example, an old version of the `DNRM2` routine.

  The x87 coprocessor stack was being mismanaged in cases involving assigned `GOTO` and `ASSIGN`.

- Fix `DTime` intrinsic so as not to truncate results to integer values (on some systems).
- Fix `SIGNAL` intrinsic so it offers portable support for 64-bit systems (such as Digital Alphas running GNU/Linux).
- Fix run-time crash involving `NAMELIST` on 64-bit machines such as Alphas.
- Fix `g77` version of `libf2c` so it no longer produces a spurious `I/O recursion` diagnostic at run time when an I/O operation (such as `READ *,I`) is interrupted in a manner that causes the program to be terminated via the `f_exit` routine (such as via `C-c`).
- Fix `g77` crash triggered by `CASE` statement with an omitted lower or upper bound.
- Fix `g77` crash compiling references to `CPU_Time` intrinsic.
- Fix `g77` crash (or apparently infinite run-time) when compiling certain complicated expressions involving `COMPLEX` arithmetic (especially multiplication).
- Fix `g77` crash on statements such as `PRINT *, (REAL(Z(I)),I=1,2)`, where `Z` is `DOUBLE COMPLEX`.
- Fix a `g++` crash.
- Support `FORMAT(I<expr>)` when expr is a compile-time constant `INTEGER` expression.
- Fix `g77` `-g` option so procedures that use `ENTRY` can be stepped through, line by line, in `gdb`.
- Fix a profiling-related bug in `gcc` back end for Intel x86 architecture.
- Allow any `REAL` argument to intrinsics `Second` and `CPU_Time`.
- Allow any numeric argument to intrinsics `Int2` and `Int8`.
- Use `tempnam`, if available, to open scratch files (as in `OPEN(STATUS='SCRATCH')` so that the `TMPDIR` environment variable, if present, is used.
- Rename the `gcc` keyword `restrict` to `__restrict__`, to avoid rejecting valid, existing, C programs. Support for `restrict` is now more like support for `complex`.
- Fix `-fpedantic` to not reject procedure invocations such as `I=J()` and `CALL FOO()`.
- Fix `-fugly-comma` to affect invocations of only external procedures. Restore rejection of gratuitous trailing omitted arguments to intrinsics, as in `I=MAX(3,4,,)`.
- Fix compiler so it accepts `-fgnu-intrinsics-*` and `-fbadu77-intrinsics-*` options.
- Improve diagnostic messages from `libf2c` so it is more likely that the printing of the active format string is limited to the string, with no trailing garbage being printed.

  (Unlike `f2c`, `g77` did not append a null byte to its compiled form of every format string specified via a `FORMAT` statement. However, `f2c` would exhibit the problem anyway for a statement like `PRINT '(I)garbage', 1` by printing `(I)garbage` as the format string.)

- Improve compilation of FORMAT expressions so that a null byte is appended to the last operand if it is a constant. This provides a cleaner run-time diagnostic as provided by `libf2c` for statements like `PRINT '(I1', 42`.
- Fix various crashes involving code with diagnosed errors.
- Fix cross-compilation bug when configuring `libf2c`.
- Improve diagnostics.
- Improve documentation and indexing.
- Upgrade to `libf2c` as of 1997-09-23. This fixes a formatted-I/O bug that afflicted 64-bit systems with 32-bit integers (such as Digital Alpha running GNU/Linux).

## In 0.5.21:

- Fix a code-generation bug introduced by 0.5.20 caused by loop unrolling (by specifying `-funroll-loops` or similar). This bug afflicted all code compiled by version 2.7.2.2.f.2 of `gcc` (C, C++, Fortran, and so on).
- Fix a code-generation bug manifested when combining local `EQUIVALENCE` with a `DATA` statement that follows the first executable statement (or is treated as an executable-context statement as a result of using the `-fpedantic` option).
- Fix a compiler crash that occured when an integer division by a constant zero is detected. Instead, when the `-W` option is specified, the `gcc` back end issues a warning about such a case. This bug afflicted all code compiled by version 2.7.2.2.f.2 of `gcc` (C, C++, Fortran, and so on).
- Fix a compiler crash that occurred in some cases of procedure inlining. (Such cases became more frequent in 0.5.20.)
- Fix a compiler crash resulting from using `DATA` or similar to initialize a `COMPLEX` variable or array to zero.
- Fix compiler crashes involving use of `AND`, `OR`, or `XOR` intrinsics.
- Fix compiler bug triggered when using a `COMMON` or `EQUIVALENCE` variable as the target of an `ASSIGN` or assigned-`GOTO` statement.
- Fix compiler crashes due to using the name of a some non-standard intrinsics (such as `FTELL` or `FPUTC`) as such and as the name of a procedure or common block. Such dual use of a name in a program is allowed by the standard.
- Place automatic arrays on the stack, even if `SAVE` or the `-fno-automatic` option is in effect. This avoids a compiler crash in some cases.
- The `-malign-double` option now reliably aligns `DOUBLE PRECISION` optimally on Pentium and Pentium Pro architectures (586 and 686 in `gcc`).
- New option `-Wno-globals` disables warnings about ``suspicious'' use of a name both as a global name and as the implicit name of an intrinsic, and warnings about disagreements over the number or natures of arguments passed to global procedures, or the natures of the procedures themselves.

  The default is to issue such warnings, which are new as of this version of `g77`.

- New option `-fno-globals` disables diagnostics about potentially fatal disagreements analysis problems, such as disagreements over the number or natures of arguments passed to global procedures, or the natures of those procedures themselves.

  The default is to issue such diagnostics and flag the compilation as unsuccessful. With this option, the diagnostics are issued as warnings, or, if `-Wno-globals` is specified, are not issued at all.

  This option also disables inlining of global procedures, to avoid compiler crashes resulting from coding errors that these diagnostics normally would identify.

- Diagnose cases where a reference to a procedure disagrees with the type of that procedure, or where disagreements about the number or nature of arguments exist. This avoids a compiler crash.
- Fix parsing bug whereby `g77` rejected a second initialization specification immediately following the first's closing `/` without an intervening comma in a `DATA` statement, and the second specification was an implied-DO list.
- Improve performance of the `gcc` back end so certain complicated expressions involving `COMPLEX` arithmetic (especially multiplication) don't appear to take forever to compile.
- Fix a couple of profiling-related bugs in `gcc` back end.
- Integrate GNU Ada's (GNAT's) changes to the back end, which consist almost entirely of bug fixes. These fixes are circa version 3.10p of GNAT.
- Include some other `gcc` fixes that seem useful in `g77`'s version of `gcc`. (See `gcc/ChangeLog` for details---compare it to that file in the vanilla `gcc-2.7.2.3.tar.gz` distribution.)
- Fix `libU77` routines that accept file and other names to strip trailing blanks from them, for consistency with other implementations. Blanks may be forcibly appended to such names by appending a single null character (`CHAR(0)`) to the significant trailing blanks.
- Fix `CHMOD` intrinsic to work with file names that have embedded blanks, commas, and so on.
- Fix `SIGNAL` intrinsic so it accepts an optional third `Status` argument.
- Fix `IDATE()` intrinsic subroutine (VXT form) so it accepts arguments in the correct order. Documentation fixed accordingly, and for `GMTIME()` and `LTIME()` as well.
- Make many changes to `libU77` intrinsics to support existing code more directly.

  Such changes include allowing both subroutine and function forms of many routines, changing `MCLOCK()` and `TIME()` to return `INTEGER(KIND=1)` values, introducing `MCLOCK8()` and `TIME8()` to return `INTEGER(KIND=2)` values, and placing functions that are intended to perform side effects in a new intrinsic group, `badu77`.

- Improve `libU77` so it is more portable.
- Add options `-fbadu77-intrinsics-delete`, `-fbadu77-intrinsics-hide`, and so on.
- Fix crashes involving diagnosed or invalid code.
- `g77` and `gcc` now do a somewhat better job detecting and diagnosing arrays that are too large to handle before these cause diagnostics during the assembler or linker phase, a compiler crash, or generation of incorrect code.
- Make some fixes to alias analysis code.
- Add support for `restrict` keyword in `gcc` front end.
- Support `gcc` version 2.7.2.3 (modified by `g77` into version 2.7.2.3.f.1), and remove support for prior versions of `gcc`.
- Incorporate GNAT's patches to the `gcc` back end into `g77`'s, so GNAT users do not need to apply GNAT's patches to build both GNAT and `g77` from the same source tree.
- Modify `make` rules and related code so that generation of Info documentation doesn't require compilation using `gcc`. Now, any ANSI C compiler should be adequate to produce the `g77` documentation (in particular, the tables of intrinsics) from scratch.
- Add `INT2` and `INT8` intrinsics.
- Add `CPU_TIME` intrinsic.
- Add `ALARM` intrinsic.
- `CTIME` intrinsic now accepts any `INTEGER` argument, not just `INTEGER(KIND=2)`.
- Warn when explicit type declaration disagrees with the type of an intrinsic invocation.
- Support `*f771` entry in `gcc` `specs` file.
- Fix typo in `make` rule `g77-cross`, used only for cross-compiling.
- Fix `libf2c` build procedure to re-archive library if previous attempt to archive was interrupted.
- Change `gcc` to unroll loops only during the last invocation (of as many as two invocations) of loop optimization.
- Improve handling of `-fno-f2c` so that code that attempts to pass an intrinsic as an actual argument, such as `CALL FOO(ABS)`, is rejected due to the fact that the run-time-library routine is, effectively, compiled with `-ff2c` in effect.
- Fix `g77` driver to recognize `-fsyntax-only` as an option that inhibits linking, just like `-c` or `-S`, and to recognize and properly handle the `-nostdlib`, `-M`, `-MM`, `-nodefaultlibs`, and `-Xlinker` options.
- Upgrade to `libf2c` as of 1997-08-16.
- Modify `libf2c` to consistently and clearly diagnose recursive I/O (at run time).
- `g77` driver now prints version information (such as produced by `g77 -v`) to `stderr` instead of `stdout`.
- The `.r` suffix now designates a Ratfor source file, to be preprocessed via the `ratfor` command, available separately.
- Fix some aspects of how `gcc` determines what kind of system is being configured and what kinds are supported. For example, GNU Linux/Alpha ELF systems now are directly supported.
- Improve diagnostics.
- Improve documentation and indexing.
- Include all pertinent files for `libf2c` that come from `netlib.bell-labs.com`; give any such files that aren't quite accurate in `g77`'s version of `libf2c` the suffix `.netlib`.
- Reserve `INTEGER(KIND=0)` for future use.

## In 0.5.20:

- The `-fno-typeless-boz` option is now the default.

  This option specifies that non-decimal-radix constants using the prefixed-radix form (such as `Z'1234'`) are to be interpreted as `INTEGER` constants. Specify `-ftypeless-boz` to cause such constants to be interpreted as typeless.

  (Version 0.5.19 introduced `-fno-typeless-boz` and its inverse.)

- Options `-ff90-intrinsics-enable` and `-fvxt-intrinsics-enable` now are the defaults.

  Some programs might use names that clash with intrinsic names defined (and now enabled) by these options or by the new `libU77` intrinsics. Users of such programs might need to compile them differently (using, for example, `-ff90-intrinsics-disable`) or, better yet, insert appropriate `EXTERNAL` statements specifying that these names are not intended to be names of intrinsics.

- The `ALWAYS_FLUSH` macro is no longer defined when building `libf2c`, which should result in improved I/O performance, especially over NFS.

  Note: If you have code that depends on the behavior of `libf2c` when built with `ALWAYS_FLUSH` defined, you will have to modify `libf2c` accordingly before building it from this and future versions of `g77`.

- Dave Love's implementation of `libU77` has been added to the version of `libf2c` distributed with and built as part of `g77`. `g77` now knows about the routines in this library as intrinsics.
- New option `-fvxt` specifies that the source file is written in VXT Fortran, instead of GNU Fortran.
- The `-fvxt-not-f90` option has been deleted, along with its inverse, `-ff90-not-vxt`.

  If you used one of these deleted options, you should re-read the pertinent documentation to determine which options, if any, are appropriate for compiling your code with this version of `g77`.

- The `-fugly` option now issues a warning, as it likely will be removed in a future version.

  (Enabling all the `-fugly-*` options is unlikely to be feasible, or sensible, in the future, so users should learn to specify only those `-fugly-*` options they really need for a particular source file.)

- The `-fugly-assumed` option, introduced in version 0.5.19, has been changed to better accommodate old and new code.
- Make a number of fixes to the `g77` front end and the `gcc` back end to better support Alpha (AXP) machines. This includes providing at least one bug-fix to the `gcc` back end for Alphas.
- Related to supporting Alpha (AXP) machines, the `LOC()` intrinsic and `%LOC()` construct now return values of integer type that is the same width (holds the same number of bits) as the pointer type on the machine.

  On most machines, this won't make a difference, whereas on Alphas, the type these constructs return is `INTEGER*8` instead of the more common `INTEGER*4`.

- Emulate `COMPLEX` arithmetic in the `g77` front end, to avoid bugs in `complex` support in the `gcc` back end. New option `-fno-emulate-complex` causes `g77` to revert the 0.5.19 behavior.
- Fix bug whereby `REAL A(1)`, for example, caused a compiler crash if `-fugly-assumed` was in effect and A was a local (automatic) array. That case is no longer affected by the new handling of `-fugly-assumed`.
- Fix `g77` command driver so that `g77 -o foo.f` no longer deletes `foo.f` before issuing other diagnostics, and so the `-x` option is properly handled.
- Enable inlining of subroutines and functions by the `gcc` back end. This works as it does for `gcc` itself---program units may be inlined for invocations that follow them in the same program unit, as long as the appropriate compile-time options are specified.
- Dummy arguments are no longer assumed to potentially alias (overlap) other dummy arguments or `COMMON` areas when any of these are defined (assigned to) by Fortran code.

  This can result in faster and/or smaller programs when compiling with optimization enabled, though on some systems this effect is observed only when `-fforce-addr` also is specified.

  New options `-falias-check`, `-fargument-alias`, `-fargument-noalias`, and `-fno-argument-noalias-global` control the way `g77` handles potential aliasing.

- The `CONJG()` and `DCONJG()` intrinsics now are compiled in-line.
- The bug-fix for 0.5.19.1 has been re-done. The `g77` compiler has been changed back to assume `libf2c` has no aliasing problems in its implementations of the `COMPLEX` (and `DOUBLE COMPLEX`) intrinsics. The `libf2c` has been changed to have no such problems.

  As a result, 0.5.20 is expected to offer improved performance over 0.5.19.1, perhaps as good as 0.5.19 in most or all cases, due to this change alone.

  Note: This change requires version 0.5.20 of `libf2c`, at least, when linking code produced by any versions of `g77` other than 0.5.19.1. Use `g77 -v` to determine the version numbers of the `libF77`, `libI77`, and `libU77` components of the `libf2c` library. (If these version numbers are not printed---in particular, if the linker complains about unresolved references to names like `g77__fvers__`---that strongly suggests your installation has an obsolete version of `libf2c`.)

- New option `-fugly-assign` specifies that the same memory locations are to be used to hold the values assigned by both statements `I = 3` and `ASSIGN 10 TO I`, for example. (Normally, `g77` uses a separate memory location to hold assigned statement labels.)
- `FORMAT` and `ENTRY` statements now are allowed to precede `IMPLICIT NONE` statements.
- Produce diagnostic for unsupported `SELECT CASE` on `CHARACTER` type, instead of crashing, at compile time.
- Fix crashes involving diagnosed or invalid code.
- Change approach to building `libf2c` archive (`libf2c.a`) so that members are added to it only when truly necessary, so the user that installs an already-built `g77` doesn't need to have write access to the build tree (whereas the user doing the build might not have access to install new software on the system).
- Support `gcc` version 2.7.2.2 (modified by `g77` into version 2.7.2.2.f.2), and remove support for prior versions of `gcc`.
- Upgrade to `libf2c` as of 1997-02-08, and fix up some of the build procedures.
- Improve general build procedures for `g77`, fixing minor bugs (such as deletion of any file named `f771` in the parent directory of `gcc/`).
- Enable full support of `INTEGER*8` available in `libf2c` and `f2c.h` so that `f2c` users may make full use of its features via the `g77` version of `f2c.h` and the `INTEGER*8` support routines in the `g77` version of `libf2c`.
- Improve `g77` driver and `libf2c` so that `g77 -v` yields version information on the library.
- The `SNGL` and `FLOAT` intrinsics now are specific intrinsics, instead of synonyms for the generic intrinsic `REAL`.
- New intrinsics have been added. These are `REALPART`, `IMAGPART`, `COMPLEX`, `LONG`, and `SHORT`.
- A new group of intrinsics, `gnu`, has been added to contain the new `REALPART`, `IMAGPART`, and `COMPLEX` intrinsics. An old group, `dcp`, has been removed.
- Complain about industry-wide ambiguous references `REAL(expr)` and `AIMAG(expr)`, where expr is `DOUBLE COMPLEX` (or any complex type other than `COMPLEX`), unless `-ff90` option specifies Fortran 90 interpretation or new `-fugly-complex` option, in conjunction with `-fnot-f90`, specifies `f2c` interpretation.
- Make improvements to diagnostics.
- Speed up compiler a bit.
- Improvements to documentation and indexing, including a new chapter containing information on one, later more, diagnostics that users are directed to pull up automatically via a message in the diagnostic itself.

  (Hence the menu item `M` for the node `Diagnostics` in the top-level menu of the Info documentation.)

## In 0.5.19.1:

- Code-generation bugs afflicting operations on complex data have been fixed.

  These bugs occurred when assigning the result of an operation to a complex variable (or array element) that also served as an input to that operation.

  The operations affected by this bug were: `CONJG()`, `DCONJG()`, `CCOS()`, `CDCOS()`, `CLOG()`, `CDLOG()`, `CSIN()`, `CDSIN()`, `CSQRT()`, `CDSQRT()`, complex division, and raising a `DOUBLE COMPLEX` operand to an `INTEGER` power. (The related generic and `Z`-prefixed intrinsics, such as `ZSIN()`, also were affected.)

  For example, `C = CSQRT(C)`, `Z = Z/C`, and `Z = Z**I` (where `C` is `COMPLEX` and `Z` is `DOUBLE COMPLEX`) have been fixed.

## In 0.5.19:

- Fix `FORMAT` statement parsing so negative values for specifiers such as `P` (e.g. `FORMAT(-1PF8.1)`) are correctly processed as negative.
- Fix `SIGNAL` intrinsic so it once again accepts a procedure as its second argument.
- A temporary kludge option provides bare-bones information on `COMMON` and `EQUIVALENCE` members at debug time.
- New `-fonetrip` option specifies FORTRAN-66-style one-trip `DO` loops.
- New `-fno-silent` option causes names of program units to be printed as they are compiled, in a fashion similar to UNIX `f77` and `f2c`.
- New `-fugly-assumed` option specifies that arrays dimensioned via `DIMENSION X(1)`, for example, are to be treated as assumed-size.
- New `-fno-typeless-boz` option specifies that non-decimal-radix constants using the prefixed-radix form (such as `Z'1234'`) are to be interpreted as `INTEGER` constants.
- New `-ff66` option is a ``shorthand'' option that specifies behaviors considered appropriate for FORTRAN 66 programs.
- New `-ff77` option is a ``shorthand'' option that specifies behaviors considered appropriate for UNIX `f77` programs.
- New `-fugly-comma` and `-fugly-logint` options provided to perform some of what `-fugly` used to do. `-fugly` and `-fno-ugly` are now ``shorthand'' options, in that they do nothing more than enable (or disable) other `-fugly-*` options.
- Fix parsing of assignment statements involving targets that are substrings of elements of `CHARACTER` arrays having names such as `READ`, `WRITE`, `GOTO`, and `REALFUNCTIONFOO`.
- Fix crashes involving diagnosed code.
- Fix handling of local `EQUIVALENCE` areas so certain cases of valid Fortran programs are not misdiagnosed as improperly extending the area backwards.
- Support `gcc` version 2.7.2.1.
- Upgrade to `libf2c` as of 1996-09-26, and fix up some of the build procedures.
- Change code generation for list-directed I/O so it allows for new versions of `libf2c` that might return non-zero status codes for some operations previously assumed to always return zero.

  This change not only affects how `IOSTAT=` variables are set by list-directed I/O, it also affects whether `END=` and `ERR=` labels are reached by these operations.

- Add intrinsic support for new `FTELL` and `FSEEK` procedures in `libf2c`.
- Modify `fseek_()` in `libf2c` to be more portable (though, in practice, there might be no systems where this matters) and to catch invalid `whence` arguments.
- Some useless warnings from the `-Wunused` option have been eliminated.
- Fix a problem building the `f771` executable on AIX systems by linking with the `-bbigtoc` option.
- Abort configuration if `gcc` has not been patched using the patch file provided in the `gcc/f/gbe/` subdirectory.
- Add options `--help` and `--version` to the `g77` command, to conform to GNU coding guidelines. Also add printing of `g77` version number when the `--verbose` (`-v`) option is used.
- Change internally generated name for local `EQUIVALENCE` areas to one based on the alphabetically sorted first name in the list of names for entities placed at the beginning of the areas.
- Improvements to documentation and indexing.

## In 0.5.18:

- Add some rudimentary support for `INTEGER*1`, `INTEGER*2`, `INTEGER*8`, and their `LOGICAL` equivalents. (This support works on most, maybe all, `gcc` targets.)

  Thanks to Scott Snyder (snyder@d0sgif.fnal.gov) for providing the patch for this!

  Among the missing elements from the support for these features are full intrinsic support and constants.

- Add some rudimentary support for the `BYTE` and `WORD` type-declaration statements. `BYTE` corresponds to `INTEGER*1`, while `WORD` corresponds to `INTEGER*2`.

  Thanks to Scott Snyder (snyder@d0sgif.fnal.gov) for providing the patch for this!

- The compiler code handling intrinsics has been largely rewritten to accommodate the new types. No new intrinsics or arguments for existing intrinsics have been added, so there is, at this point, no intrinsic to convert to `INTEGER*8`, for example.
- Support automatic arrays in procedures.
- Reduce space/time requirements for handling large sparsely initialized aggregate arrays. This improvement applies to only a subset of the general problem to be addressed in 0.6.
- Treat initial values of zero as if they weren't specified (in DATA and type-declaration statements). The initial values will be set to zero anyway, but the amount of compile time processing them will be reduced, in some cases significantly (though, again, this is only a subset of the general problem to be addressed in 0.6).

  A new option, `-fzeros`, is introduced to enable the traditional treatment of zeros as any other value.

- With `-ff90` in force, `g77` incorrectly interpreted `REAL(Z)` as returning a `REAL` result, instead of as a `DOUBLE PRECISION` result. (Here, `Z` is `DOUBLE COMPLEX`.)

  With `-fno-f90` in force, the interpretation remains unchanged, since this appears to be how at least some F77 code using the `DOUBLE COMPLEX` extension expected it to work.

  Essentially, `REAL(Z)` in F90 is the same as `DBLE(Z)`, while in extended F77, it appears to be the same as `REAL(REAL(Z))`.

- An expression involving exponentiation, where both operands were type `INTEGER` and the right-hand operand was negative, was erroneously evaluated.
- Fix bugs involving `DATA` implied-`DO` constructs (these involved an errant diagnostic and a crash, both on good code, one involving subsequent statement-function definition).
- Close `INCLUDE` files after processing them, so compiling source files with lots of `INCLUDE` statements does not result in being unable to open `INCLUDE` files after all the available file descriptors are used up.
- Speed up compiling, especially of larger programs, and perhaps slightly reduce memory utilization while compiling (this is not the improvement planned for 0.6 involving large aggregate areas)---these improvements result from simply turning off some low-level code to do self-checking that hasn't been triggered in a long time.
- Introduce three new options that implement optimizations in the `gcc` back end (GBE). These options are `-fmove-all-movables`, `-freduce-all-givs`, and `-frerun-loop-opt`, which are enabled, by default, for Fortran compilations. These optimizations are intended to help toon Fortran programs.
- Patch the GBE to do a better job optimizing certain kinds of references to array elements.
- Due to patches to the GBE, the version number of `gcc` also is patched to make it easier to manage installations, especially useful if it turns out a `g77` change to the GBE has a bug.

  The `g77`-modified version number is the `gcc` version number with the string `.f.n` appended, where `f` identifies the version as enhanced for Fortran, and n is `1` for the first Fortran patch for that version of `gcc`, `2` for the second, and so on.

  So, this introduces version 2.7.2.f.1 of `gcc`.

- Make several improvements and fixes to diagnostics, including the removal of two that were inappropriate or inadequate.
- Warning about two successive arithmetic operators, produced by `-Wsurprising`, now produced only when both operators are, indeed, arithmetic (not relational/boolean).
- `-Wsurprising` now warns about the remaining cases of using non-integral variables for implied-`DO` loops, instead of these being rejected unless `-fpedantic` or `-fugly` specified.
- Allow `SAVE` of a local variable or array, even after it has been given an initial value via `DATA`, for example.
- Introduce an Info version of `g77` documentation, which supercedes `gcc/f/CREDITS`, `gcc/f/DOC`, and `gcc/f/PROJECTS`. These files will be removed in a future release. The files `gcc/f/BUGS`, `gcc/f/INSTALL`, and `gcc/f/NEWS` now are automatically built from the texinfo source when distributions are made.

  This effort was inspired by a first pass at translating `g77-0.5.16/f/DOC` that was contributed to Craig by David Ronis (ronis@onsager.chem.mcgill.ca).

- New `-fno-second-underscore` option to specify that, when `-funderscoring` is in effect, a second underscore is not to be appended to Fortran names already containing an underscore.
- Change the way iterative `DO` loops work to follow the F90 standard. In particular, calculation of the iteration count is still done by converting the start, end, and increment parameters to the type of the `DO` variable, but the result of the calculation is always converted to the default `INTEGER` type.

  (This should have no effect on existing code compiled by `g77`, but code written to assume that use of a wider type for the `DO` variable will result in an iteration count being fully calculated using that wider type (wider than default `INTEGER`) must be rewritten.)

- Support `gcc` version 2.7.2.
- Upgrade to `libf2c` as of 1996-03-23, and fix up some of the build procedures.

  Note that the email addresses related to `f2c` have changed---the distribution site now is named `netlib.bell-labs.com`, and the maintainer's new address is dmg@bell-labs.com.

## In 0.5.17:

- Fix serious bug in `g77 -v` command that can cause removal of a system's `/dev/null` special file if run by user `root`.

  All users of version 0.5.16 should ensure that they have not removed `/dev/null` or replaced it with an ordinary file (e.g. by comparing the output of `ls -l /dev/null` with `ls -l /dev/zero`. If the output isn't basically the same, contact your system administrator about restoring `/dev/null` to its proper status).

  This bug is particularly insidious because removing `/dev/null` as a special file can go undetected for quite a while, aside from various applications and programs exhibiting sudden, strange behaviors.

  I sincerely apologize for not realizing the implications of the fact that when `g77 -v` runs the `ld` command with `-o /dev/null` that `ld` tries to remove the executable it is supposed to build (especially if it reports unresolved references, which it should in this case)!

- Fix crash on `CHARACTER*(*) FOO` in a main or block data program unit.
- Fix crash that can occur when diagnostics given outside of any program unit (such as when input file contains `@foo`).
- Fix crashes, infinite loops (hangs), and such involving diagnosed code.
- Fix `ASSIGN`'ed variables so they can be `SAVE`'d or dummy arguments, and issue clearer error message in cases where target of `ASSIGN` or `ASSIGN`ed `GOTO`/`FORMAT` is too small (which should never happen).
- Make `libf2c` build procedures work on more systems again by eliminating unnecessary invocations of `ld -r -x` and `mv`.
- Fix omission of `-funix-intrinsics-···` options in list of permitted options to compiler.
- Fix failure to always diagnose missing type declaration for `IMPLICIT NONE`.
- Fix compile-time performance problem (which could sometimes crash the compiler, cause a hang, or whatever, due to a bug in the back end) involving exponentiation with a large `INTEGER` constant for the right-hand operator (e.g. `I**32767`).
- Fix build procedures so cross-compiling `g77` (the `fini` utility in particular) is properly built using the host compiler.
- Add new `-Wsurprising` option to warn about constructs that are interpreted by the Fortran standard (and `g77`) in ways that are surprising to many programmers.
- Add `ERF()` and `ERFC()` as generic intrinsics mapping to existing `ERF`/`DERF` and `ERFC`/`DERFC` specific intrinsics.

  Note: You should specify `INTRINSIC ERF,ERFC` in any code where you might use these as generic intrinsics, to improve likelihood of diagnostics (instead of subtle run-time bugs) when using a compiler that doesn't support these as intrinsics (e.g. `f2c`).

- Remove from `-fno-pedantic` the diagnostic about `DO` with non-`INTEGER` index variable; issue that under `-Wsurprising` instead.
- Clarify some diagnostics that say things like ``ignored'' when that's misleading.
- Clarify diagnostic on use of `.EQ.`/`.NE.` on `LOGICAL` operands.
- Minor improvements to code generation for various operations on `LOGICAL` operands.
- Minor improvement to code generation for some `DO` loops on some machines.
- Support `gcc` version 2.7.1.
- Upgrade to `libf2c` as of 1995-11-15.

## In 0.5.16:

- Fix a code-generation bug involving complicated `EQUIVALENCE` statements not involving `COMMON`.
- Fix code-generation bugs involving invoking ``gratis'' library procedures in `libf2c` from code compiled with `-fno-f2c` by making these procedures known to `g77` as intrinsics (not affected by -fno-f2c). This is known to fix code invoking `ERF()`, `ERFC()`, `DERF()`, and `DERFC()`.
- Update `libf2c` to include netlib patches through 1995-08-16, and `#define` `WANT_LEAD_0` to 1 to make `g77`-compiled code more consistent with other Fortran implementations by outputting leading zeros in formatted and list-directed output.
- Fix a code-generation bug involving adjustable dummy arrays with high bounds whose primaries are changed during procedure execution, and which might well improve code-generation performance for such arrays compared to `f2c` plus `gcc` (but apparently only when using `gcc-2.7.0` or later).
- Fix a code-generation bug involving invocation of `COMPLEX` and `DOUBLE COMPLEX` `FUNCTION`s and doing `COMPLEX` and `DOUBLE COMPLEX` divides, when the result of the invocation or divide is assigned directly to a variable that overlaps one or more of the arguments to the invocation or divide.
- Fix crash by not generating new optimal code for `X**I` if `I` is nonconstant and the expression is used to dimension a dummy array, since the `gcc` back end does not support the necessary mechanics (and the `gcc` front end rejects the equivalent construct, as it turns out).
- Fix crash on expressions like `COMPLEX**INTEGER`.
- Fix crash on expressions like `(1D0,2D0)**2`, i.e. raising a `DOUBLE COMPLEX` constant to an `INTEGER` constant power.
- Fix crashes and such involving diagnosed code.
- Diagnose, instead of crashing on, statement function definitions having duplicate dummy argument names.
- Fix bug causing rejection of good code involving statement function definitions.
- Fix bug resulting in debugger not knowing size of local equivalence area when any member of area has initial value (via `DATA`, for example).
- Fix installation bug that prevented installation of `g77` driver. Provide for easy selection of whether to install copy of `g77` as `f77` to replace the broken code.
- Fix `gcc` driver (affects `g77` thereby) to not gratuitously invoke the `f771` program (e.g. when `-E` is specified).
- Fix diagnostic to point to correct source line when it immediately follows an `INCLUDE` statement.
- Support more compiler options in `gcc`/`g77` when compiling Fortran files. These options include `-p`, `-pg`, `-aux-info`, `-P`, correct setting of version-number macros for preprocessing, full recognition of `-O0`, and automatic insertion of configuration-specific linker specs.
- Add new intrinsics that interface to existing routines in `libf2c`: `ABORT`, `DERF`, `DERFC`, `ERF`, `ERFC`, `EXIT`, `FLUSH`, `GETARG`, `GETENV`, `IARGC`, `SIGNAL`, and `SYSTEM`. Note that `ABORT`, `EXIT`, `FLUSH`, `SIGNAL`, and `SYSTEM` are intrinsic subroutines, not functions (since they have side effects), so to get the return values from `SIGNAL` and `SYSTEM`, append a final argument specifying an `INTEGER` variable or array element (e.g. `CALL SYSTEM('rm foo',ISTAT)`).
- Add new intrinsic group named `unix` to contain the new intrinsics, and by default enable this new group.
- Move `LOC()` intrinsic out of the `vxt` group to the new `unix` group.
- Improve `g77` so that `g77 -v` by itself (or with certain other options, including `-B`, `-b`, `-i`, `-nostdlib`, and `-V`) reports lots more useful version info, and so that long-form options `gcc` accepts are understood by `g77` as well (even in truncated, unambiguous forms).
- Add new `g77` option `--driver=name` to specify driver when default, `gcc`, isn't appropriate.
- Add support for `#` directives (as output by the preprocessor) in the compiler, and enable generation of those directives by the preprocessor (when compiling `.F` files) so diagnostics and debugging info are more useful to users of the preprocessor.
- Produce better diagnostics, more like `gcc`, with info such as `In function `foo':` and `In file included from...:`.
- Support `gcc`'s `-fident` and `-fno-ident` options.
- When `-Wunused` in effect, don't warn about local variables used as statement-function dummy arguments or `DATA` implied-`DO` iteration variables, even though, strictly speaking, these are not uses of the variables themselves.
- When `-W -Wunused` in effect, don't warn about unused dummy arguments at all, since there's no way to turn this off for individual cases (`g77` might someday start warning about these)---applies to `gcc` versions 2.7.0 and later, since earlier versions didn't warn about unused dummy arguments.
- New option `-fno-underscoring` that inhibits transformation of names (by appending one or two underscores) so users may experiment with implications of such an environment.
- Minor improvement to `gcc/f/info` module to make it easier to build `g77` using the native (non-`gcc`) compiler on certain machines (but definitely not all machines nor all non-`gcc` compilers). Please do not report bugs showing problems compilers have with macros defined in `gcc/f/target.h` and used in places like `gcc/f/expr.c`.
- Add warning to be printed for each invocation of the compiler if the target machine `INTEGER`, `REAL`, or `LOGICAL` size is not 32 bits, since `g77` is known to not work well for such cases (to be fixed in Version 0.6---see Actual Bugs We Haven't Fixed Yet).
- Lots of new documentation (though work is still needed to put it into canonical GNU format).
- Build `libf2c` with `-g0`, not `-g2`, in effect (by default), to produce smaller library without lots of debugging clutter.

## In 0.5.15:

- Fix bad code generation involving `X**I` and temporary, internal variables generated by `g77` and the back end (such as for `DO` loops).
- Fix crash given `CHARACTER A;DATA A/.TRUE./`.
- Replace crash with diagnostic given `CHARACTER A;DATA A/1.0/`.
- Fix crash or other erratic behavior when null character constant (`''`) is encountered.
- Fix crash or other erratic behavior involving diagnosed code.
- Fix code generation for external functions returning type `REAL` when the `-ff2c` option is in force (which it is by default) so that `f2c` compatibility is indeed provided.
- Disallow `COMMON I(10)` if `I` has previously been specified with an array declarator.
- New `-ffixed-line-length-n` option, where n is the maximum length of a typical fixed-form line, defaulting to 72 columns, such that characters beyond column n are ignored, or n is `none`, meaning no characters are ignored. does not affect lines with `&` in column 1, which are always processed as if `-ffixed-line-length-none` was in effect.
- No longer generate better code for some kinds of array references, as `gcc` back end is to be fixed to do this even better, and it turned out to slow down some code in some cases after all.
- In `COMMON` and `EQUIVALENCE` areas with any members given initial values (e.g. via `DATA`), uninitialized members now always initialized to binary zeros (though this is not required by the standard, and might not be done in future versions of `g77`). Previously, in some `COMMON`/`EQUIVALENCE` areas (essentially those with members of more than one type), the uninitialized members were initialized to spaces, to cater to `CHARACTER` types, but it seems no existing code expects that, while much existing code expects binary zeros.

## In 0.5.14:

- Don't emit bad code when low bound of adjustable array is nonconstant and thus might vary as an expression at run time.
- Emit correct code for calculation of number of trips in `DO` loops for cases where the loop should not execute at all. (This bug affected cases where the difference between the begin and end values was less than the step count, though probably not for floating-point cases.)
- Fix crash when extra parentheses surround item in `DATA` implied-`DO` list.
- Fix crash over minor internal inconsistencies in handling diagnostics, just substitute dummy strings where necessary.
- Fix crash on some systems when compiling call to `MVBITS()` intrinsic.
- Fix crash on array assignment `TYPEddd(···)=···`, where ddd is a string of one or more digits.
- Fix crash on `DCMPLX()` with a single `INTEGER` argument.
- Fix various crashes involving code with diagnosed errors.
- Support `-I` option for `INCLUDE` statement, plus `gcc`'s `header.gcc` facility for handling systems like MS-DOS.
- Allow `INCLUDE` statement to be continued across multiple lines, even allow it to coexist with other statements on the same line.
- Incorporate Bellcore fixes to `libf2c` through 1995-03-15---this fixes a bug involving infinite loops reading EOF with empty list-directed I/O list.
- Remove all the `g77`-specific auto-configuration scripts, code, and so on, except for temporary substitutes for bsearch() and strtoul(), as too many configure/build problems were reported in these areas. People will have to fix their systems' problems themselves, or at least somewhere other than `g77`, which expects a working ANSI C environment (and, for now, a GNU C compiler to compile `g77` itself).
- Complain if initialized common redeclared as larger in subsequent program unit.
- Warn if blank common initialized, since its size can vary and hence related warnings that might be helpful won't be seen.
- New `-fbackslash` option, on by default, that causes `\` within `CHARACTER` and Hollerith constants to be interpreted a la GNU C. Note that this behavior is somewhat different from `f2c`'s, which supports only a limited subset of backslash (escape) sequences.
- Make `-fugly-args` the default.
- New `-fugly-init` option, on by default, that allows typeless/Hollerith to be specified as initial values for variables or named constants (`PARAMETER`), and also allows character<->numeric conversion in those contexts---turn off via `-fno-ugly-init`.
- New `-finit-local-zero` option to initialize local variables to binary zeros. This does not affect whether they are `SAVE`d, i.e. made automatic or static.
- New `-Wimplicit` option to warn about implicitly typed variables, arrays, and functions. (Basically causes all program units to default to `IMPLICIT NONE`.)
- `-Wall` now implies `-Wuninitialized` as with `gcc` (i.e. unless `-O` not specified, since `-Wuninitialized` requires `-O`), and implies `-Wunused` as well.
- `-Wunused` no longer gives spurious messages for unused `EXTERNAL` names (since they are assumed to refer to block data program units, to make use of libraries more reliable).
- Support `%LOC()` and `LOC()` of character arguments.
- Support null (zero-length) character constants and expressions.
- Support `f2c`'s `IMAG()` generic intrinsic.
- Support `ICHAR()`, `IACHAR()`, and `LEN()` of character expressions that are valid in assignments but not normally as actual arguments.
- Support `f2c`-style `&` in column 1 to mean continuation line.
- Allow `NAMELIST`, `EXTERNAL`, `INTRINSIC`, and `VOLATILE` in `BLOCK DATA`, even though these are not allowed by the standard.
- Allow `RETURN` in main program unit.
- Changes to Hollerith-constant support to obey Appendix C of the standard:
  - Now padded on the right with zeros, not spaces.
  - Hollerith ``format specifications'' in the form of arrays of non-character allowed.
  - Warnings issued when non-space truncation occurs when converting to another type.
  - When specified as actual argument, now passed by reference to `INTEGER` (padded on right with spaces if constant too small, otherwise fully intact if constant wider the `INTEGER` type) instead of by value.

  Warning: `f2c` differs on the interpretation of `CALL FOO(1HX)`, which it treats exactly the same as `CALL FOO('X')`, but which the standard and `g77` treat as `CALL FOO(%REF('X '))` (padded with as many spaces as necessary to widen to `INTEGER`), essentially.

- Changes and fixes to typeless-constant support:
  - Now treated as a typeless double-length `INTEGER` value.
  - Warnings issued when overflow occurs.
  - Padded on the left with zeros when converting to a larger type.
  - Should be properly aligned and ordered on the target machine for whatever type it is turned into.
  - When specified as actual argument, now passed as reference to a default `INTEGER` constant.
- `%DESCR()` of a non-`CHARACTER` expression now passes a pointer to the expression plus a length for the expression just as if it were a `CHARACTER` expression. For example, `CALL FOO(%DESCR(D))`, where `D` is `REAL*8`, is the same as `CALL FOO(D,%VAL(8)))`.
- Name of multi-entrypoint master function changed to incorporate the name of the primary entry point instead of a decimal value, so the name of the master function for `SUBROUTINE X` with alternate entry points is now `__g77_masterfun_x`.
- Remove redundant message about zero-step-count `DO` loops.
- Clean up diagnostic messages, shortening many of them.
- Fix typo in `g77` man page.
- Clarify implications of constant-handling bugs in `f/BUGS`.
- Generate better code for `**` operator with a right-hand operand of type `INTEGER`.
- Generate better code for `SQRT()` and `DSQRT()`, also when `-ffast-math` specified, enable better code generation for `SIN()` and `COS()`.
- Generate better code for some kinds of array references.
- Speed up lexing somewhat (this makes the compilation phase noticeably faster).