出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2013/01/15 17:40:17」(JST)
FORTRAN | |
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The Fortran Automatic Coding System for the IBM 704 (15 October 1956), the first Programmer's Reference Manual for Fortran
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パラダイム | 手続き型・構造化・命令型・オブジェクト指向 |
登場時期 | 1957年 |
開発者 | IBM(ジョン・バッカス) |
最新リリース | Fortran 2008 |
型付け | 強い静的型付け |
主な処理系 | Absoft, Cray, CUDA, Fortran Builder, GFortran, G95, Intel, Lahey/Fujitsu, Open Watcom, Pathscale, PGI, Silverfrost, Sun, XL Fortran, Visual Fortran ほか |
影響を与えた言語 | ALGOL 58, BASIC, PL/I, C |
プラットフォーム | z/OS, z/VM, z/VSE, MCP, VOS3, ACOS, GCOS, VMS, OS/400, UNIX, Linux, Windows, Mac OS, CP/M, MS-DOS ほか |
テンプレートを表示 |
プログラミング言語
■カテゴリ / ■テンプレート
FORTRAN(フォートラン)は、1954年にIBMのジョン・バッカスによって考案されたコンピュータにおける最初の、広く使われた高水準言語である。1956年に最初のマニュアルが、1957年にIBM 704用の最初のコンパイラがリリースされた。名前「FORTRAN」は「数式翻訳」を意味する英語「formula translation」に由来し、FORTRAN 77やFortran 90などの末尾の数字は規格が制定された年を示している。
FORTRANは科学技術計算に向いた手続き型プログラミング言語であり、その長い歴史の間に開発された非常に多くの数学関数やサブルーチンを数値解析ソフトウェアの形で持っている。また、並列計算の並列性を明示的に書くことができ最適化が行いやすく、そのため他の言語より高速である等の理由から[1]、数値予報および気候モデル、構造力学における有限要素法、計算流体力学、計算物理学、計算機化学、計量経済学、動物と植物の品種改良などの大規模な計算を行う分野において、スーパーコンピュータで使われている[2]。
また、ちょうどC言語に対するC++言語のように、Fortran 90/Fortran 95の言語仕様は、FORTRAN 77の頃と比べればかなり拡張され進歩したものとなっている。最新のソースコードは初期のものと比較すると、ほとんど別の言語のように見える。 初期の頃は、変数名が大文字6文字までで、動的な記憶領域の確保ができないなど多くの制約があったが、それらの制限は無くなり、Fortran77から構造化プログラミングが、Fortran 90からモジュラープログラミング、配列演算とユーザー定義総称関数が、Fortran 95からHigh Performance Fortranが、Fortran 2003からオブジェクト指向が、Fortran 2008 からはコンカレント・コンピューティング(並行計算)が導入された。
なお、大文字でFORTRANと表記した場合、FORTRAN 77以前のFORTRANを指し、Fortranと表記した場合、Fortran 90以降を指すことがある。
目次
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Fortran 90/95の特徴は、以下のように要約される[3] 。
広く使われていたFORTRAN 77 の特徴は、以下のように要約される。
ジョン・バッカスは1953年末、メインフレームコンピュータIBM 704のプログラムを開発するにあたり、アセンブリ言語に代わるものを開発することをIBMの上司に提案した。歴史的なFORTRAN開発チームはRichard Goldberg、Sheldon F. Best、Harlan Herrick、Peter Sheridan、Roy Nutt、 Robert Nelson、Irving Ziller、Lois Haibt、David Sayreというメンバーで構成された[4]。
The IBM Mathematical Formula Translating System のドラフト仕様は1954年中旬に作成された。1956年10月にFORTRANの最初のマニュアルが作成され、コンパイラが1957年4月に開発された。顧客はアセンブリ言語で記述されたコードに匹敵するパフォーマンスが得られない限り高級言語を採用しないので、最初から最適化コンパイラが開発された。
この新しい方法がハンドアセンブルより高速に動作するかどうかには疑いの目があったが、プログラム中の命令数を1/20に削減できるので急速に受け入れられていった。IBMの社内誌であるThinkに掲載された1979年のインタビューでバッカスは「私がこの仕事をしたのは面倒くさがりだったからです。私はプログラムを書くことが好きではなかったので、IBM 701でミサイルの軌道計算プログラムを開発したときに、プログラムの開発を簡単にするためにプログラミングシステムを作り始めました。」[5]と語っている。
FORTRANは科学者の間で数学を応用したプログラムの記述に広く用いられたことから、より高速で効率的なコードを出力しようとする原動力となった。FORTRANに組み込まれた複素数型は特に電気工学のような専門的なアプリケーションに適していた。
1960年までに様々なバージョンのFORTRANがIBM 709、IBM 650、IBM 1620、IBM 7090で動作していた。FORTRANのユーザー数は急増し、コンピューターメーカーがFORTANコンパイラをこぞって提供したので、1963年までには40を超えるFORTRANコンパイラが存在していた。こうしたことから、FORTRANはアーキテクチャの異なる様々なコンピュータを広くサポートする最初の言語と言える。
FORTRAN開発の歴史は、初期のコンパイラ技術の歴史そのものといえる。FORTRANで効率的なコードを出力したいという強い要求からコンパイラの実装技術が大きく進歩した。
IBM 704用に開発された最初のFORTRANは32の命令をもっていた。
IBM 1401版は革新的な65パスのコンパイラであり、わずか8k語の磁気コアメモリで動作する。コアに記録されたプログラムが段階的に実行可能なコードへと変換されて上書きされる。変換されたコードは機械語ではなく、UCSD PascalのPコードが生まれるよりも20年も前ながら、中間コードを利用していた。
IBMのFORTRAN IIは1958年に開発された。主な改良点は手続き型プログラミングのサポートであり、サブルーチンや関数を定義できるようになった。
その後、FORTRAN IIのデータ型には、DOUBLE PRECISION
(倍精度型)とCOMPLEX
(複素数型)が追加された。
IBMは1958年にFORTRAN IIIを開発していた。いくつかの新機能に加えインラインアセンブラが可能であった。しかしながらこのバージョンは販売されなかった。704 FORTRANやFORTRAN IIと同様に、FORTRAN IIIにも移植の妨げになるような機種依存の機能があった。他のベンダーから販売されていたFORTRANも初期は同様の問題を抱えていた。
IBMは1961年に顧客の要望を受けFORTRAN IVの開発を開始した。READ INPUT TAPE
のようなFORTRAN IIの機種依存部分を削除したほか、LOGICAL
(論理型)、論理演算、算術IF文の代替となる論理IF文が加えられた。この時のターゲットマシンはワードマシンだったので、整数値は235の範囲で定義されていた。また、実数の精度は227、倍精度実数の精度は254までだった。FORTRAN IVは1962年にIBM 7030(通称ストレッチ)用がリリースされ、後にIBM 7090版とIBM 7094版がリリースされた。
1965年には国家規格であるANSI X3.4.3 FORTRANに準拠した。
American Standards Association(現ANSI)がFORTRANの米国規格を委員会で制定するようになったことはFORTRANの歴史の要である。1966年に2つの異なる言語が制定された。一つは当時既にデファクトスタンダードであったFORTRAN IVを基にしたFORTRANであり、もう一つはFORTRAN IIを基にして機種依存部分を取り除いたBasic FORTRANである。最初に制定されたFORTRANの規格は後にFORTRAN 66と呼ばれた。
FORTRAN 66 規格のリリース後、コンパイラ・ベンダーは多くの拡張を"標準Fortran"に導入し、1966の規格の改訂を始めるようにANSIを促した。 この改訂は1977年に制定され、最終的な改訂案は1978年4月に新しいFORTRAN標準として承認された。 この新しい標準はFORTRAN 77として知られ、FORTRAN 66後の多くの変更を追加し、多くの重要な機能を加えた:
IF
とEND IF
ステートメント、オプショナルなELSE
とELSE IF
ステートメント。改善された言語サポートのための構造化プログラミング。OPEN
, CLOSE
, と INQUIRE
文。IMPLICIT
文。CHARACTER
データ・タイプ。文字の入出力と処理のための大幅な増補。PARAMETER
定数を指定するためのステートメント。SAVE
ステートメント。LGE, LGT, LLE, LLT
)。この規格の改訂において、多くの機能は除去されるか変えられ、以前の標準に合致する多くのプログラムはおそらく無効になった。 この時点で除去はX3J3の代替だけが許容された。だからコンセプト "不賛成"はANSI標準においては利用できなかった。しかし、コンフリクトリストの24アイテム(Appendix A2 of X3.9-1978を見よ)ループホールスとパスロジカルケースは以前の標準規格から許容されたが、しかし滅多に使用されない。 少数の機能は慎重に除去された:
DIMENSION A(10,5)
Y= A(11,1)
一般にFortran 90 として知られている規格は、大幅に発表が遅れたもののFORTRAN 77の正当な継承者であり、最終的に1991年にISO規格、1992年にANSI規格としてリリースされた。この抜本的な改訂では1978年のFORTRAN 77規格制定からのプログラミング技術における大幅な変化を反映するために、以下の多くの新しい機能が加えられた:
if (x<0) then x=0 end if
abcdefghijklmnopqrstuvwxyz12345=0.0e0
! これは"!"を用いたコメントです
x(1:n)=r(1:n)*cos(a(1:n))
integer::a(10) real(8)::b(10) a=f(x) where(a>0) b=-1.0 elsewhere b=1.0 end where
function sample(x) result(y) !配列yを返す integer,parameter::nn=4 real::y(nn)=(/ 1,2,3,4 /) !配列のコンストラクタと定数による初期化 .... end function sample
module my_lib !モジュール interface function sample(x) real,intent(in)::x(:)!コンパイル時に変数の型の整合性とデータの入出力方向がチェックされる。 .... end function sample end interface end module
real,allocatable::temp(:) allocate(temp(nn)) deallocate(temp)
do i=1,nn if (b(i) /= 0) then a(i) = 1.0 / b(i) else exit end if end do
select case (sw) case ('++') a = a + 1 case ('--') a = a - 1 case default a = 0 end select
a=1.0e0_kind(1.0d0)
以前のバージョンとは異なり、Fortran 90は、何の機能も削除しなかった。 (Appendix B.1 は『この規格の、削除した機能のリストは空である。』と言っている。) つまり、FORTRAN 77に準拠したプログラムは、Fortran 90にもまた準拠している。 そして、両方の規格で、その動作が定義づけられた項目は使用可能でなければならない。 一部の機能はFortran 95で『削除』され、また機能の小さな部分は『時代遅れ』と認定されて将来の規格で除去されることが予定された。
時代遅れの機能 | 例 | 状態 / Fortran 95での予定 |
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算術 IF-statement | IF (X) 10, 20, 30 |
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非-整数 DO パラメータ あるいは制御変数 | DO 9 X= 1.7, 1.6, -0.1 |
削除 |
Shared DO-loop termination or termination with a statement |
DO 9 J= 1, 10
|
|
ブロック外部からの END IFへのブランチ |
66 GO TO 77 ; . . .
|
削除 |
Alternate return | CALL SUBR( X, Y *100, *200 ) |
|
PAUSE文 | PAUSE 600 |
削除 |
ASSIGN statement と assigned GO TO statement |
100 . . .
|
削除 |
Assigned FORMAT specifiers | ASSIGN F TO 606 |
削除 |
H edit descriptors | 606 FORMAT ( 9H1GOODBYE. ) |
削除 |
Computed GO TO statement | GO TO (10, 20, 30, 40), index |
(時代遅れ) |
文関数 | FOIL( X, Y )= X**2 + 2*X*Y + Y**2 |
(時代遅れ) |
DATA statements among executable statements |
X= 27.3
|
(時代遅れ) |
CHARACTER* form of CHARACTER declaration | CHARACTER*8 STRING ! Use CHARACTER(8) |
(時代遅れ) |
Assumed character length functions | ||
固定フォームソースコード | * Column 1 contains * or ! or C for comments. C Column 6 for continuation. |
program helloworld print *, "Hello, world." end program helloworld
Fortran 95は、マイナーな改訂版である。 ほとんどは、Fortran 90規格の、いくつかの大きな問題を解決するためのものである。 それにも係わらず、Fortran 95もまた年号を付加されている。 それは、Fortranの拡張として定義される並列言語、HPF (High Performance Fortran:ハイ・パフォーマンスFortran)の一部導入によることは明白である。なお、本格的なHPFは、地球シミュレータ等で使用されている[2]:
forall
と階層化されたwhere
がベクトル化のために追加された。pure
と elemental
プロセジャーが追加された。allocatable
アレイがスコープから出た時に自動的にdeallocate
されることの明確な定義が追加された。多くの内部関数は拡張された。一例としてmaxloc
内部関数にdim
引数が追加された
Fortran 90で時代遅れとされた、いくつかの機能はFortran 95から削除された。
REAL
とDOUBLE PRECISION
変数を使用したDO
ステートメントは削除された。END IF
ステートメントへのブロック外部からのブランチは削除された。PAUSE
ステートメントは削除された。ASSIGN
とASSIGN
型GOTO
ステートメント、ASSIGN
フォーマット指定は削除された。H
エディット記述子は削除された。Fortran 95への重要な追加は、一般にはAllocatable TRとして知られる、ISO technical report、TR-15581: Enhanced Data Type Facilitiesである。この仕様は、Fortran 2003準拠のFortran コンパイラより前に、ALLOCATABLE
アレイの強化した用法を定義した。そのような用法は、プロセジャーのダミー引数リストとしての派生タイプコンポーネントALLOCATABLE
アレイと、関数の返し値を含む。 ALLOCATABLE
アレイは、POINTER
-ベース・アレイより好ましいものである。なぜなら、ALLOCATABLE
アレイは、スコープから抜けたとき、Fortran 95による自動的なdeallocateを保証しメモリリークの可能性を無くすからである。
エリアシングはarrayの参照において最適化の障害にならず、Fortranコンパイラがポインタ-ベース・アレイより高速なコードを生成することを可能にする。
他の重要なFortran 95への追加は ISO technical report TR-15580: 浮動小数点例外ハンドリングである。 一般にはIEEE TRとして知られている、この仕様はIEEE 浮動小数点演算と例外ハンドリングを定義する、
必須のベース言語(ISO/IEC 1539-1:1997に定義)以外に、Fortran 95 言語もまた2つのオプショナルなモジュールを含む:
それらは、共にマルチパート国際標準を構成する(ISO/IEC 1539)。規格の開発者によれば、『オプショナル・パートは必要なものを完備した機能を記述している、それは多くのコンパイラ・インプリメンターとユーザーから要求されてきたものである。しかし、それらは、全てのFortran標準に合致するコンパイラは十分な一般性を持たないと考えられていた。それにも係わらず、もし標準に合致したFortranがそのようなオプションを提供するなら、『それらの機能は、標準規格の適切なパートに記述に従って提供されなければならない。』
Fortran 2003はメジャーな改訂であり、たくさんの新しい機能を導入した。 FORTRAN2003における新しい機能の包括的なサマリーは、Fortran Working Group (WG5)のオフィシャルWebサイトから得ることができる[6]。
この記事から、このバージョンが含む大幅な強化は:
FLUSH
ステートメント、キーワードの規則化、エラーメッセージへのアクセス。Fortran 2003 への重要な追加は、ISO technical report TR-19767である:
Fortranにおけるモジュール機能の強化。このレポートは、submodulesを提供する。これは、FortranのモジュールをよりModula-2のモジュールに近づける。 これらは、Adaのプライベート・チャイルド・サブユニットに似ている。 これは分離したプログラムユニットとして表現すべきモジュールの仕様と実装を可能にし、大規模なライブラリのパッケージ化を改善し、インターフェース定義を公開しても企業秘密を保持することを可能にし、コンパイレーション・カスケードを防ぐ。
最新の規格であり一般にはFortran 2008として知られているISO/IEC 1539-1:2010は2010年9月に承認された [7]。 Fortran 95と同様に、これはマイナー・アップグレードである。 Fortran 2003の明確化と訂正と共に、新しい特長も導入された。 新しい特長は、以下を含む:
ファイナル・ドラフト・スタンダード(FDIS)は、ドキュメントN1830として利用できる [8]。
Fortran 2008における重要な追加は、ISOテクニカルスペシフィケーション(TS) 29113のFortranにおけるC言語とのより高いインターオペラビリティであり [9] [10] 、2012年5月のISOの承認に向けてまとめられた。 C言語の配列へのFortranアクセスに関してタイプとランクを無視する仕様が加えられた。
JISにおける仕様は、以下のように変遷している。
1967年に、JISとして制定された。この時は、以下の3つの水準ごとに独立したJISが制定された。共通したタイトルは「電子計算機プログラム用言語 FORTRAN」だった。以下に水準間のおおよその違いを記す。
なお、1971、1976年に若干の改訂がなされている。
国際標準化機構(ISO)は、米国規格協会(ANSI)の X3J3 が作成した FORTRAN の規格 X3.9-1978 を ISO 1539-1980 として定めた。基本水準(subset language)と上位水準(full language)の2種類の水準からなっていた。これを基にして、同じく2水準の JIS C 6201-1982 が制定された。なお、1987年に、JISの分類が変更になり、この規格は JIS X 3001-1982 となった。内容には変更はない。
FORTRAN 77を基に他の言語の特徴を組み込み、言語仕様を近代化しようとしたが、そのため仕様がなかなか決まらず、1991年に ISO/IEC 1539:1991として制定された。JISではそれを受け、JIS X 3001:1994が制定された。
Fortranの言語仕様は、年代によってかなり変化して来ている。他のプログラミング言語で実装された構造化プログラミングの機能などがどんどん取り入れられて来ているからである。
FORTRANは、情報処理分野で広く使われていたため、学校や会社の教育(情報処理技術者向け教育)で利用された。教育向けには、より詳細なエラー情報を出すための拡張がWaterloo大学でWATFOR(後にWATFIV)コンパイラとして実装された。この実装は日本の大学でも使われた。また2006年4月にはNAGから教育用FORTRAN統合開発環境Fortran Builderが発売された。 Fortran BuilderにはFortran言語が学習できる28回の授業コンテンツが標準搭載されている。
Fortranは科学技術計算用の言語なので、スーパーコンピュータでのプログラミング言語としてよく用いられる。
FortranはC言語のように、スタック等を使わず、コンパイル時に静的に記憶領域を確保するのが基本である。そのため、コンパイラはコードを最適化しやすいという利点がある。
Fortranは、いまでも科学技術用行列演算での使用が基本であり、ベクトル型スーパーコンピュータは、Fortranを使ったプログラムで使用することが多い。そこで、スーパーコンピュータの高速演算機能を有効に使うための工夫がなされた。その1つの例としては、自動ベクトル化機能である。ベクトル型のスーパーコンピュータは、多くの演算を同時に行うベクトル演算機能がハードウェアで提供されている。この機能を有効に使うために、FortranのDOループをベクトル演算装置で演算させるために、自動的にベクトル命令にする機能が提供された。また、DOループ内のベクトル演算に適さないものをDOループ外に追い出す機能などもある。たとえば、
DO 100 I=1,N A(I) = B(I) * C(I) 100 CONTINUE
のようなDO構文は、ほとんどの場合、1から数個のベクトル演算命令にコンパイルされる。そのほかにもDOループの中にIF文を含むような例、たとえば、
DO 110 I=1,N IF (A(I) .LE. LIMIT) THEN B(I) = A(I) * Z END IF 110 CONTINUE
のようなものもベクトル化できる場合がある。これは、いったんAの各要素がLIMIT以下かどうかを示すマスクベクトルを作成し、Aという配列(=ベクトル)に、変数Zをかけるとき、マスクベクトルを参照してベクトル演算を行うことによって、DOループをベクトル化する。
このような作業は、すべてコンパイラが行い、利用者にはできるだけ負担をかけないようにしている。しかし、より高度なベクトル化を行うために、最適化を行う支援ツールが用意されている場合もある。
コンピュータ上で日本語の文字を扱えるようになると、FORTRANでも日本語を扱う需要が出てきた。そのため、各社(メインフレームを作成していたメーカ)では、独自に言語仕様に日本語の文字を扱えるように拡張した。そのため、各社で日本語の扱い方が異なる事態になった。そこで、JEIDAでは1985年に、JEIDA-42で日本語FORTRANを策定した。
FORTRANで日本語を扱う場合、変数名等には日本語は使えず、文字列や日本語を扱うための専用の型(日本語型)、日本語を入出力するためのFORMAT文の要素の拡張が行われた。
FORTRAN 77に先立つFORTRANベースのプリプロセッサは使いやすい言語を提供するために広く使われた。プリプロセスされたコードは、任意のマシンの標準のFORTRANコンパイラでコンパイルすることができるという利点を持つ。これらのプリプロセッサは通常、構造化プログラミング、6文字よりも長い変数名、追加のデータ型、条件付きコンパイル、さらにはマクロ機能をサポートしていた。
ポピュラーなプリプロセッサとしてFLECSとiftran、MORTRAN、SFtran、S-Fortran、Ratfor、Ratfivがあった。例えば、RatforとRatfivはCライクな言語を実装し、プリプロセスにより標準的なFORTRAN 66コードを出力した。Fortran言語の進歩にもかかわらず、プリプロセッサは条件付きコンパイルとマクロ置換のために使用され続けている。
LRLTRANは、ローレンス放射線研究所で、ベクトル演算および動的な記憶、システムのプログラミングをサポートする他の拡張機能を提供するために開発され、ディストリビューションにはLTSSオペレーティングシステムが含まれていた。Fortran 95規格は、任意の条件付きコンパイルの機能を定義するオプションパート3を備えている。この機能は、しばしば 『CoCo』と呼ばれている。多くのFORTRANコンパイラは、それらのシステムにCプリプロセッサのサブセットを取り込んだ。
SIMSCRIPTは、大規模な離散システムのモデリングとシミュレーションのためのアプリケーションに特化したFortranのプリプロセッサである。
FORTRAN-Sは、日本電気によって開発された。
プログラミング言語Fは、FORTRANのEQUIVALENCE文などの、冗長、非構造化、非推奨な機能を削除したFortran 95のクリーンなサブセットとして設計された。 FはFortran 90で追加された配列演算の機能を使い、FORTRAN 77とFortran 90で追加された制御文を用い、構造化プログラミングで廃止された制御文を削除した。設計者はFを 『特に教育や科学技術計算に適した、構造化された配列プログラミング言語である。』 と述べている[11]。
[ヘルプ] |
gzip
ped PostScript file, FTP.nag.co.ukウィキブックスにFortran関連の解説書・教科書があります。 |
The Fortran Automatic Coding System for the IBM 704 (15 October 1956), the first Programmer's Reference Manual for Fortran |
|
Paradigm(s) | multi-paradigm: structured, imperative (procedural, object-oriented), generic |
---|---|
Appeared in | 1957 |
Designed by | John Backus |
Developer | John Backus & IBM |
Stable release | Fortran 2008 (ISO/IEC 1539-1:2010) (2010) |
Typing discipline | strong, static, manifest |
Major implementations | Absoft, Cray, GFortran, G95, IBM, Intel, Lahey/Fujitsu, Open Watcom, PathScale, PGI, Silverfrost, Oracle, XL Fortran, Visual Fortran, others |
Influenced by | Speedcoding |
Influenced | ALGOL 58, BASIC, C, PL/I, PACT I, MUMPS, Ratfor |
Usual filename extensions | .f , .for , .f90 , .f95 |
Fortran (previously FORTRAN) is a general-purpose, imperative programming language that is especially suited to numeric computation and scientific computing. Originally developed by IBM at their campus in south San Jose, California[1] in the 1950s for scientific and engineering applications, Fortran came to dominate this area of programming early on and has been in continual use for over half a century in computationally intensive areas such as numerical weather prediction, finite element analysis, computational fluid dynamics, computational physics and computational chemistry. It is one of the most popular languages in the area of high-performance computing [2] and is the language used for programs that benchmark and rank the world's fastest supercomputers.
Fortran (a blend derived from The IBM Mathematical Formula Translating System) encompasses a lineage of versions, each of which evolved to add extensions to the language while usually retaining compatibility with previous versions. Successive versions have added support for structured programming and processing of character-based data (FORTRAN 77), array programming, modular programming and generic programming (Fortran 90), high performance Fortran (Fortran 95), object-oriented programming (Fortran 2003) and concurrent programming (Fortran 2008).
Contents
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The names of earlier versions of the language through FORTRAN 77 were conventionally spelled in all-caps (FORTRAN 77 was the version in which the use of lowercase letters in keywords was strictly nonstandard). The capitalization has been dropped in referring to newer versions beginning with Fortran 90. The official language standards now refer to the language as "Fortran". Because the capitalization was never completely consistent in actual usage, this article adopts the convention of using the all-caps FORTRAN in referring to versions of the language up to FORTRAN 77 and the title-caps Fortran in referring to versions of the language from Fortran 90 onward. This convention is reflected in the capitalization of FORTRAN in the ANSI X3.9-1966 (FORTRAN 66) and ANSI X3.9-1978 (FORTRAN 77) standards and the title caps Fortran in the ANSI X3.198-1992 (Fortran 90), ISO/IEC 1539-1:1997 (Fortran 95) and ISO/IEC 1539-1:2004 (Fortran 2003) standards.
In late 1953, John W. Backus submitted a proposal to his superiors at IBM to develop a more practical alternative to assembly language for programming their IBM 704 mainframe computer. Backus' historic FORTRAN team consisted of programmers Richard Goldberg, Sheldon F. Best, Harlan Herrick, Peter Sheridan, Roy Nutt, Robert Nelson, Irving Ziller, Lois Haibt, and David Sayre.[3] Its concepts included easier entry of equations into a computer, an idea developed by J. Halcombe Laning and demonstrated in his GEORGE compiler of 1952.[4]
A draft specification for The IBM Mathematical Formula Translating System was completed by mid-1954. The first manual for FORTRAN appeared in October 1956, with the first FORTRAN compiler delivered in April 1957. This was the first optimizing compiler, because customers were reluctant to use a high-level programming language unless its compiler could generate code whose performance was comparable to that of hand-coded assembly language.[5]
While the community was skeptical that this new method could possibly outperform hand-coding, it reduced the number of programming statements necessary to operate a machine by a factor of 20, and quickly gained acceptance. John Backus said during a 1979 interview with Think, the IBM employee magazine, "Much of my work has come from being lazy. I didn't like writing programs, and so, when I was working on the IBM 701, writing programs for computing missile trajectories, I started work on a programming system to make it easier to write programs."[6]
The language was widely adopted by scientists for writing numerically intensive programs, which encouraged compiler writers to produce compilers that could generate faster and more efficient code. The inclusion of a complex number data type in the language made Fortran especially suited to technical applications such as electrical engineering.
By 1960, versions of FORTRAN were available for the IBM 709, 650, 1620, and 7090 computers. Significantly, the increasing popularity of FORTRAN spurred competing computer manufacturers to provide FORTRAN compilers for their machines, so that by 1963 over 40 FORTRAN compilers existed. For these reasons, FORTRAN is considered to be the first widely used programming language supported across a variety of computer architectures.
The development of FORTRAN paralleled the early evolution of compiler technology, and many advances in the theory and design of compilers were specifically motivated by the need to generate efficient code for FORTRAN programs.
The initial release of FORTRAN for the IBM 704 contained 32 statements, including:
DIMENSION
and EQUIVALENCE
statementsIF
statement.IF
statements for checking exceptions (ACCUMULATOR OVERFLOW
, QUOTIENT OVERFLOW
, and DIVIDE CHECK
); and IF
statements for manipulating sense switches and sense lightsGOTO
, computed GOTO
, ASSIGN
, and assigned GOTO
DO
loopsFORMAT
, READ
, READ INPUT TAPE
, WRITE
, WRITE OUTPUT TAPE
, PRINT
, and PUNCH
READ TAPE
, READ DRUM
, WRITE TAPE
, and WRITE DRUM
END FILE
, REWIND
, and BACKSPACE
PAUSE
, STOP
, and CONTINUE
FREQUENCY
statement (for providing optimization hints to the compiler).The arithmetic IF
statement was similar to a three-way branch instruction on the IBM 704. However, the 704 branch instructions all contained only one destination address (e.g., TZE — Transfer AC Zero, TNZ — Transfer AC Not Zero, TPL — Transfer AC Plus, TMI — Transfer AC Minus). The machine (and its successors in the 700/7000 series) did have a three-way skip instruction (CAS — Compare AC with Storage), but using this instruction to implement the IF
would consume 4 instruction words, require the constant Zero in a word of storage, and take 3 machine cycles to execute; using the Transfer instructions to implement the IF
could be done in 1 to 3 instruction words, required no constants in storage, and take 1 to 3 machine cycles to execute. An optimizing compiler like FORTRAN would most likely select the more compact and usually faster Transfers instead of the Compare (use of Transfers also allowed the FREQUENCY
statement to optimize IF
s, which could not be done using the Compare). Also the Compare considered −0 and +0 to be different values while the Transfer Zero and Transfer Not Zero considered them to be the same.
The FREQUENCY
statement in FORTRAN was used originally and optionally to give branch probabilities for the three branch cases of the Arithmetic IF statement to bias the way code was generated and order of the basic blocks of code generated, in the global optimisation sense, were arranged in memory for optimality. The first FORTRAN compiler used this weighting to do a Monte Carlo simulation of the run-time generated code at compile time. It was very sophisticated for its time. This technique is documented in the original article in 1957 on the first FORTRAN compiler implementation by J. Backus et al. Many years later, the FREQUENCY
statement had no effect on the code, and was treated as a comment statement, since the compilers no longer did this kind of compile-time simulation.
Below is a part of the 1957 paper, "The FORTRAN Automatic Coding System" by Backus et al., with this snippet on the FREQUENCY statement and its use in a compile-time Monte Carlo simulation of the run-time to optimise the code generated. Quoting …
The fundamental unit of program is the basic block; a basic block is a stretch of program which has a single entry point and a single exit point. The purpose of section 4 is to prepare for section 5 a table of predecessors (PRED table) which enumerates the basic blocks and lists for every basic block each of the basic blocks which can be its immediate predecessor in flow, together with the absolute frequency of each such basic block link. This table is obtained by an actual "execution" of the program in Monte-Carlo fashion, in which the outcome of conditional transfers arising out of IF-type statements and computed GO TO'S is determined by a random number generator suitably weighted according to whatever FREQUENCY statements have been provided.
Before the development of disk files, text editors and terminals, programs were most often entered on a keypunch keyboard onto 80 column punched cards, one line to a card. The resulting deck of cards would be fed into a card reader to be compiled. See Computer programming in the punched card era.
Originally Fortran programs were written in a fixed column format. A letter "C" in column 1 caused the entire card to be treated as a comment and ignored by the compiler. Otherwise, the card was divided into four fields. Columns 1 to 5 were the label field: a sequence of digits here was taken as a label for the purpose of a GOTO or a FORMAT reference in a WRITE or READ statement. Column 6 was a continuation field: a non-blank character here caused the card to be taken as a continuation of the statement on the previous card. Columns 7 to 72 served as the statement field. Columns 73 to 80 were ignored, so they could be used for identification information. One such use was punching a sequence number which could be used to re-order cards if a stack of cards was dropped, though in practice this was reserved for stable, production programs. An IBM 519 could be used to copy a program deck and add sequence numbers. Some early compilers, e.g. the IBM 650's, had additional restrictions.[7] Later compilers relaxed most fixed format restrictions.
Within the statement field, blanks were generally ignored, allowing the programmer to omit space between tokens for brevity, or include spaces within identifiers for clarity (for example, AVG OF X
was a valid identifier, and equivalent to AVGOFX
).
Early FORTRAN compilers did not support recursion in subroutines. Early computer architectures did not support the concept of a stack, and when they did directly support subroutine calls, the return location was often stored in a single fixed location adjacent to the subroutine code, which does not permit a subroutine to be called again before a previous call of the subroutine has returned. Although not specified in Fortran 77, many F77 compilers supported recursion as an option, while it became a standard in Fortran 90.[8]
IBM's FORTRAN II appeared in 1958. The main enhancement was to support procedural programming by allowing user-written subroutines and functions which returned values, with parameters passed by reference. The COMMON statement provided a way for subroutines to access common (or global) variables. Six new statements were introduced:
SUBROUTINE
, FUNCTION
, and END
CALL
and RETURN
COMMON
Over the next few years, FORTRAN II would also add support for the DOUBLE PRECISION
and COMPLEX
data types.
This program, for Heron's formula, reads one data card containing three 5-digit integers A, B, and C as input. If A, B, and C cannot represent the sides of a triangle in plane geometry, then the program's execution will end with an error code of "STOP 1". Otherwise, an output line will be printed showing the input values for A, B, and C, followed by the computed AREA of the triangle as a floating-point number with 2 digits after the decimal point.
C AREA OF A TRIANGLE WITH A STANDARD SQUARE ROOT FUNCTION C INPUT - CARD READER UNIT 5, INTEGER INPUT C OUTPUT - LINE PRINTER UNIT 6, REAL OUTPUT C INPUT ERROR DISPLAY ERROR OUTPUT CODE 1 IN JOB CONTROL LISTING READ INPUT TAPE 5, 501, IA, IB, IC 501 FORMAT (3I5) C IA, IB, AND IC MAY NOT BE NEGATIVE C FURTHERMORE, THE SUM OF TWO SIDES OF A TRIANGLE C IS GREATER THAN THE THIRD SIDE, SO WE CHECK FOR THAT, TOO IF (IA) 777, 777, 701 701 IF (IB) 777, 777, 702 702 IF (IC) 777, 777, 703 703 IF (IA+IB-IC) 777,777,704 704 IF (IA+IC-IB) 777,777,705 705 IF (IB+IC-IA) 777,777,799 777 STOP 1 C USING HERON'S FORMULA WE CALCULATE THE C AREA OF THE TRIANGLE 799 S = FLOATF (IA + IB + IC) / 2.0 AREA = SQRT( S * (S - FLOATF(IA)) * (S - FLOATF(IB)) * + (S - FLOATF(IC))) WRITE OUTPUT TAPE 6, 601, IA, IB, IC, AREA 601 FORMAT (4H A= ,I5,5H B= ,I5,5H C= ,I5,8H AREA= ,F10.2, + 13H SQUARE UNITS) STOP END
IBM also developed a FORTRAN III in 1958 that allowed for inline assembler code among other features; however, this version was never released as a product. Like the 704 FORTRAN and FORTRAN II, FORTRAN III included machine-dependent features that made code written in it unportable from machine to machine. Early versions of FORTRAN provided by other vendors suffered from the same disadvantage.
FORTRAN was provided for the IBM 1401 by an innovative 63-pass compiler that ran in only 8k of core. It kept the program in memory and loaded overlays that gradually transformed it, in place, into executable form, as described by Haines et al.[9] The executable form was not machine language; rather it was interpreted, anticipating UCSD Pascal P-code by two decades.
Starting in 1961, as a result of customer demands, IBM began development of a FORTRAN IV that removed the machine-dependent features of FORTRAN II (such as READ INPUT TAPE
), while adding new features such as a LOGICAL
data type, logical Boolean expressions and the logical IF statement as an alternative to the arithmetic IF statement. FORTRAN IV was eventually released in 1962, first for the IBM 7030 ("Stretch") computer, followed by versions for the IBM 7090 and IBM 7094.
By 1965, FORTRAN IV was supposed to be compliant with the "standard" being developed by the American Standards Association X3.4.3 FORTRAN Working Group.[10]
At about this time FORTRAN IV had started to become an important educational tool and implementations such as Waterloo University's WATFOR and WATFIV were created to simplify the complex compile and link processes of earlier compilers.
Perhaps the most significant development in the early history of FORTRAN was the decision by the American Standards Association (now ANSI) to form a committee sponsored by BEMA, the Business Equipment Manufacturers Association, to develop an "American Standard Fortran." The resulting two standards, approved in March 1966, defined two languages, FORTRAN (based on FORTRAN IV, which had served as a de facto standard), and Basic FORTRAN (based on FORTRAN II, but stripped of its machine-dependent features). The FORTRAN defined by the first standard, officially denoted X3.9-1966, became known as FORTRAN 66 (although many continued to refer to it as FORTRAN IV, the language upon which the standard was largely based). FORTRAN 66 effectively became the first "industry-standard" version of FORTRAN. FORTRAN 66 included:
SUBROUTINE
, FUNCTION
, and BLOCK DATA
program unitsINTEGER
, REAL
, DOUBLE PRECISION
, COMPLEX
, and LOGICAL
data typesCOMMON
, DIMENSION
, and EQUIVALENCE
statementsDATA
statement for specifying initial valuesEXTERNAL
(e.g., library) functionsGOTO
, assigned GOTO
, and computed GOTO
statementsIF
and arithmetic (three-way) IF
statementsDO
loopsREAD
, WRITE
, BACKSPACE
, REWIND
, and ENDFILE
statements for sequential I/OFORMAT
statementCALL
, RETURN
, PAUSE
, and STOP
statementsDATA
and FORMAT
statements, and as actual arguments to proceduresAfter the release of the FORTRAN 66 standard, compiler vendors introduced a number of extensions to "Standard Fortran", prompting ANSI committee X3J3 in 1969 to begin work on revising the 1966 standard, under sponsorship of CBEMA, the Computer Business Equipment Manufacturers Association (formerly BEMA). Final drafts of this revised standard circulated in 1977, leading to formal approval of the new FORTRAN standard in April 1978. The new standard, known as FORTRAN 77 and officially denoted X3.9-1978, added a number of significant features to address many of the shortcomings of FORTRAN 66:
IF
and END IF
statements, with optional ELSE
and ELSE IF
clauses, to provide improved language support for structured programmingOPEN
, CLOSE
, and INQUIRE
statements for improved I/O capabilityIMPLICIT
statementCHARACTER
data type, with vastly expanded facilities for character input and output and processing of character-based dataPARAMETER
statement for specifying constantsSAVE
statement for persistent local variablesLGE, LGT, LLE, LLT
) for lexical comparison of strings, based upon the ASCII collating sequence. (These ASCII functions were demanded by the U.S. Department of Defense, in their conditional approval vote.[citation needed])In this revision of the standard, a number of features were removed or altered in a manner that might invalidate previously standard-conforming programs. (Removal was the only allowable alternative to X3J3 at that time, since the concept of "deprecation" was not yet available for ANSI standards.) While most of the 24 items in the conflict list (see Appendix A2 of X3.9-1978) addressed loopholes or pathological cases permitted by the previous standard but rarely used, a small number of specific capabilities were deliberately removed, such as:
DIMENSION A(10,5)
Y= A(11,1)
Control Data Corporation computers had another version of FORTRAN 77, called Minnesota FORTRAN (MNF), designed especially for student use, with variations in output constructs, special uses of COMMONs and DATA statements, optimizations code levels for compiling, and detailed error listings, extensive warning messages, and debugs.[11]
The development of a revised standard to succeed FORTRAN 77 would be repeatedly delayed as the standardization process struggled to keep up with rapid changes in computing and programming practice. In the meantime, as the "Standard FORTRAN" for nearly fifteen years, FORTRAN 77 would become the historically most important dialect.
An important practical extension to FORTRAN 77 was the release of MIL-STD-1753 in 1978.[12] This specification, developed by the U.S. Department of Defense, standardized a number of features implemented by most FORTRAN 77 compilers but not included in the ANSI FORTRAN 77 standard. These features would eventually be incorporated into the Fortran 90 standard.
DO WHILE
and END DO
statementsINCLUDE
statementIMPLICIT NONE
variant of the IMPLICIT
statementThe IEEE 1003.9 POSIX Standard, released in 1991, provided a simple means for FORTRAN 77 programmers to issue POSIX system calls.[13] Over 100 calls were defined in the document — allowing access to POSIX-compatible process control, signal handling, file system control, device control, procedure pointing, and stream I/O in a portable manner.
The much delayed successor to FORTRAN 77, informally known as Fortran 90 (and prior to that, Fortran 8X), was finally released as ISO/IEC standard 1539:1991 in 1991 and an ANSI Standard in 1992. In addition to changing the official spelling from FORTRAN to Fortran, this major revision added many new features to reflect the significant changes in programming practice that had evolved since the 1978 standard:
X(1:N)=R(1:N)*COS(A(1:N))
WHERE
statement for selective array assignmentRECURSIVE
proceduresALLOCATABLE
attribute and the ALLOCATE
and DEALLOCATE
statementsPOINTER
attribute, pointer assignment, and NULLIFY
statement to facilitate the creation and manipulation of dynamic data structuresEND DO
statement for loop termination, and EXIT
and CYCLE
statements for terminating normal DO
loop iterations in an orderly waySELECT
. . . CASE
construct for multi-way selectionUnlike the previous revision, Fortran 90 did not delete any features. (Appendix B.1 says, "The list of deleted features in this standard is empty.") Any standard-conforming FORTRAN 77 program is also standard-conforming under Fortran 90, and either standard should be usable to define its behavior.
A small set of features were identified as "obsolescent" and expected to be removed in a future standard.
Obsolescent feature | Example | Status / Fate in Fortran 95 |
---|---|---|
Arithmetic IF-statement | IF (X) 10, 20, 30 |
|
Non-integer DO parameters or control variables | DO 9 X= 1.7, 1.6, -0.1 |
Deleted |
Shared DO-loop termination or termination with a statement |
DO 9 J= 1, 10
|
|
Branching to END IF from outside a block |
66 GO TO 77 ; . . .
|
Deleted |
Alternate return | CALL SUBR( X, Y *100, *200 ) |
|
PAUSE statement | PAUSE 600 |
Deleted |
ASSIGN statement and assigned GO TO statement |
100 . . .
|
Deleted |
Assigned FORMAT specifiers | ASSIGN F TO 606 |
Deleted |
H edit descriptors | 606 FORMAT ( 9H1GOODBYE. ) |
Deleted |
Computed GO TO statement | GO TO (10, 20, 30, 40), index |
(obsolete) |
Statement functions | FOIL( X, Y )= X**2 + 2*X*Y + Y**2 |
(obsolete) |
DATA statements among executable statements |
X= 27.3
|
(obsolete) |
CHARACTER* form of CHARACTER declaration | CHARACTER*8 STRING ! Use CHARACTER(8) |
(obsolete) |
Assumed character length functions | CHARACTER*(*) STRING |
(obsolete)[14] |
Fixed form source code | Column 1 contains *, ! or C for comments. Column 6 for continuation. |
program helloworld print *, "Hello, world." end program helloworld
Fortran 95, published officially as ISO/IEC 1539-1:1997, was a minor revision, mostly to resolve some outstanding issues from the Fortran 90 standard. Nevertheless, Fortran 95 also added a number of extensions, notably from the High Performance Fortran specification:
FORALL
and nested WHERE
constructs to aid vectorizationPURE
and ELEMENTAL
proceduresALLOCATABLE
arrays are automatically deallocated when they go out of scope.A number of intrinsic functions were extended (for example a dim
argument was added to the maxloc
intrinsic).
Several features noted in Fortran 90 to be "obsolescent" were removed from Fortran 95:
DO
statements using REAL
and DOUBLE PRECISION
variablesEND IF
statement from outside its blockPAUSE
statementASSIGN
and assigned GOTO
statement, and assigned format specifiersH
edit descriptor.An important supplement to Fortran 95 was the ISO technical report TR-15581: Enhanced Data Type Facilities, informally known as the Allocatable TR. This specification defined enhanced use of ALLOCATABLE
arrays, prior to the availability of fully Fortran 2003-compliant Fortran compilers. Such uses include ALLOCATABLE
arrays as derived type components, in procedure dummy argument lists, and as function return values. (ALLOCATABLE
arrays are preferable to POINTER
-based arrays because ALLOCATABLE
arrays are guaranteed by Fortran 95 to be deallocated automatically when they go out of scope, eliminating the possibility of memory leakage. In addition, aliasing is not an issue for optimization of array references, allowing compilers to generate faster code than in the case of pointers.)
Another important supplement to Fortran 95 was the ISO technical report TR-15580: Floating-point exception handling, informally known as the IEEE TR. This specification defined support for IEEE floating-point arithmetic and floating point exception handling.
In addition to the mandatory "Base language" (defined in ISO/IEC 1539-1 : 1997), the Fortran 95 language also includes two optional modules:
which, together, compose the multi-part International Standard (ISO/IEC 1539).
According to the standards developers, "the optional parts describe self-contained features which have been requested by a substantial body of users and/or implementors, but which are not deemed to be of sufficient generality for them to be required in all standard-conforming Fortran compilers." Nevertheless, if a standard-conforming Fortran does provide such options, then they "must be provided in accordance with the description of those facilities in the appropriate Part of the Standard."
Fortran 2003, officially published as ISO/IEC 1539-1:2004, is a major revision introducing many new features. A comprehensive summary of the new features of Fortran 2003 is available at the Fortran Working Group (ISO/IEC JTC1/SC22/WG5) official Web site.[15]
From that article, the major enhancements for this revision include:
VOLATILE
attribute, explicit type specification in array constructors and allocate statements, pointer enhancements, extended initialization expressions, and enhanced intrinsic procedures.FLUSH
statement, regularization of keywords, and access to error messages.An important supplement to Fortran 2003 was the ISO technical report TR-19767: Enhanced module facilities in Fortran. This report provided submodules, which make Fortran modules more similar to Modula-2 modules. They are similar to Ada private child subunits. This allows the specification and implementation of a module to be expressed in separate program units, which improves packaging of large libraries, allows preservation of trade secrets while publishing definitive interfaces, and prevents compilation cascades.
The most recent standard, ISO/IEC 1539-1:2010, informally known as Fortran 2008, was approved in September 2010.[16] As with Fortran 95, this is a minor upgrade, incorporating clarifications and corrections to Fortran 2003, as well as introducing a select few new capabilities. The new capabilities include:
The Final Draft international Standard (FDIS) is available as document N1830.[17]
An important supplement to Fortran 2008 is the ISO Technical Specification (TS) 29113 on Further Interoperability of Fortran with C,[18][19] which has been submitted to ISO in May 2012 for approval. The specification adds support for accessing the array descriptor from C and allows to ignore the type and rank of arguments.
Since Fortran has been in use for more than fifty years, there is a vast body of Fortran in daily use throughout the scientific and engineering communities. It is the primary language for some of the most intensive supercomputing tasks, such as weather and climate modeling, computational fluid dynamics, computational chemistry, computational economics, animal breeding, plant breeding and computational physics. Even today, half a century later, many of the floating-point benchmarks to gauge the performance of new computer processors are still written in Fortran (e.g., CFP2006, the floating-point component of the SPEC CPU2006 benchmarks).
This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (September 2011) |
Portability was a problem in the early days because there was no agreed standard—not even IBM's reference manual—and computer companies vied to differentiate their offerings from others by providing incompatible features. Standards have improved portability. The 1966 standard provided a reference syntax and semantics, but vendors continued to provide incompatible extensions. Although careful programmers were coming to realize that use of incompatible extensions caused expensive portability problems, and were therefore using programs such as The PFORT Verifier, it was not until after the 1977 standard, when the National Bureau of Standards (now NIST) published FIPS PUB 69, that processors purchased by the U.S. Government were required to diagnose extensions of the standard. Rather than offer two processors, essentially every compiler eventually had at least an option to diagnose extensions.
Incompatible extensions were not the only portability problem. For numerical calculations, it is important to take account of the characteristics of the arithmetic. This was addressed by Fox et al. in the context of the 1966 standard by the PORT library. The ideas therein became widely used, and were eventually incorporated into the 1990 standard by way of intrinsic inquiry functions. The widespread (now almost universal) adoption of the IEEE 754 standard for binary floating-point arithmetic has essentially removed this problem.
Access to the computing environment (e.g. the program's command line, environment variables, textual explanation of error conditions) remained a problem until it was addressed by the 2003 standard.
Large collections of "library" software that could be described as being loosely related to engineering and scientific calculations, such as graphics libraries, have been written in C, and therefore access to them presented a portability problem. This has been addressed by incorporation of C interoperability into the 2003 standard.
It is now possible (and relatively easy) to write an entirely portable program in Fortran, even without recourse to a preprocessor.
Fortran 5 was a programming language marketed by Data General Corp in the late 1970s and early 1980s, for the Nova, Eclipse, and MV line of computers. It had an optimizing compiler that was quite good for minicomputers of its time. The language most closely resembles Fortran 66. The name is a pun on the earlier Fortran IV.
Fortran V was a programming language distributed by Control Data Corporation in 1968 for the CDC 6600 series. The language was based upon Fortran IV.[20]
Univac also offered a compiler for the 1100 series known as Fortran V. A spinoff of Univac Fortran V was Athena Fortran.
Fortran 6 or Visual Fortran 2001 was licensed to Compaq by Microsoft. They have licensed Compaq Visual Fortran and have provided the Visual Studio 5 environment interface for Compaq v6 up to v6.1.[21]
Vendors of high-performance scientific computers (e.g., Burroughs, CDC, Cray, Honeywell, IBM, Texas Instruments, and UNIVAC) added extensions to Fortran to take advantage of special hardware features such as instruction cache, CPU pipelines, and vector arrays. For example, one of IBM's FORTRAN compilers (H Extended IUP) had a level of optimization which reordered the machine code instructions to keep multiple internal arithmetic units busy simultaneously. Another example is CFD, a special variant of Fortran designed specifically for the ILLIAC IV supercomputer, running at NASA's Ames Research Center. IBM Research Labs also developed an extended FORTRAN-based language called "VECTRAN" for processing of vectors and matrices.
Object-Oriented Fortran was an object-oriented extension of Fortran, in which data items can be grouped into objects, which can be instantiated and executed in parallel. It was available for Sun, Iris, iPSC, and nCUBE, but is no longer supported.
Such machine-specific extensions have either disappeared over time or have had elements incorporated into the main standards; the major remaining extension is OpenMP, which is a cross-platform extension for shared memory programming. One new extension, Coarray Fortran, is intended to support parallel programming.
"FOR TRANSIT" was the name of a reduced version of the IBM 704 FORTRAN language, which was implemented for the IBM 650, using a translator program developed at Carnegie [22] in the late 1950s. The following comment appears in the IBM Reference Manual ("FOR TRANSIT Automatic Coding System" C28-4038, Copyright 1957, 1959 by IBM):
The FORTRAN system was designed for a more complex machine than the 650, and consequently some of the 32 statements found in the FORTRAN Programmer's Reference Manual are not acceptable to the FOR TRANSIT system. In addition, certain restrictions to the FORTRAN language have been added. However, none of these restrictions make a source program written for FOR TRANSIT incompatible with the FORTRAN system for the 704.
The permissible statements were:
Up to ten subroutines could be used in one program.
FOR TRANSIT statements were limited to columns 7 thru 56, only. Punched cards were used for input and output on the IBM 650. Three passes were required to translate source code to the "IT" language, then to compile the IT statements into SOAP assembly language, and finally to produce the object program, which could then be loaded into the machine to run the program (using punched cards for data input, and outputting results onto punched cards).
Two versions existed for the 650s with a 2000 word memory drum: FOR TRANSIT I (S) and FOR TRANSIT II, the latter for machines equipped with indexing registers and automatic floating point decimal (bi-quinary) arithmetic. Appendix A of the manual included wiring diagrams for the IBM 533 card reader/punch control panel.
Prior to FORTRAN 77, a number of preprocessors were commonly used to provide a friendlier language, with the advantage that the preprocessed code could be compiled on any machine with a standard FORTRAN compiler. These preprocesors would typically support structured programming, variable names longer than six characters, additional data types, conditional compilation, and even macro capabilities. Popular preprocessors included FLECS, iftran, MORTRAN, SFtran, S-Fortran, Ratfor, and Ratfiv. Ratfor and Ratfiv, for example, implemented a C-like language, outputting preprocessed code in standard FORTRAN 66. Despite advances in the Fortran language, preprocessors continue to be used for conditional compilation and macro substitution.
LRLTRAN was developed at the Lawrence Radiation Laboratory to provide support for vector arithmetic and dynamic storage, among other extensions to support systems programming. The distribution included the LTSS operating system.
The Fortran-95 Standard includes an optional Part 3 which defines an optional conditional compilation capability. This capability is often referred to as "CoCo".
Many Fortran compilers have integrated subsets of the C preprocessor into their systems.
SIMSCRIPT is an application specific Fortran preprocessor for modeling and simulating large discrete systems.
The F programming language was designed to be a clean subset of Fortran 95 that attempted to remove the redundant, unstructured, and deprecated features of Fortran, such as the EQUIVALENCE
statement. F retains the array features added in Fortran 90, and removes control statements that were made obsolete by structured programming constructs added to both Fortran 77 and Fortran 90. F is described by its creators as "a compiled, structured, array programming language especially well suited to education and scientific computing."[23]
Lahey and Fujitsu teamed up to create Fortran for the Microsoft .NET platform.[24]
The following program illustrates dynamic memory allocation and array-based operations, two features introduced with Fortran 90. Particularly noteworthy is the absence of DO
loops and IF
/THEN
statements in manipulating the array; mathematical operations are applied to the array as a whole. Also apparent is the use of descriptive variable names and general code formatting that conform with contemporary programming style. This example computes an average over data entered interactively.
program average ! Read in some numbers and take the average ! As written, if there are no data points, an average of zero is returned ! While this may not be desired behavior, it keeps this example simple implicit none real, dimension(:), allocatable :: points integer :: number_of_points real :: average_points=0., positive_average=0., negative_average=0. write (*,*) "Input number of points to average:" read (*,*) number_of_points allocate (points(number_of_points)) write (*,*) "Enter the points to average:" read (*,*) points ! Take the average by summing points and dividing by number_of_points if (number_of_points > 0) average_points = sum(points) / number_of_points ! Now form average over positive and negative points only if (count(points > 0.) > 0) then positive_average = sum(points, points > 0.) / count(points > 0.) end if if (count(points < 0.) > 0) then negative_average = sum(points, points < 0.) / count(points < 0.) end if deallocate (points) ! Print result to terminal write (*,'(a,g12.4)') 'Average = ', average_points write (*,'(a,g12.4)') 'Average of positive points = ', positive_average write (*,'(a,g12.4)') 'Average of negative points = ', negative_average end program average
During the same Fortran Standards Committee meeting at which the name "FORTRAN 77" was chosen, a technical proposal was incorporated into the official distribution, bearing the title, "Letter O considered harmful". This proposal purported to address the confusion that sometimes arises between the letter "O" and the numeral zero, by eliminating the letter from allowable variable names. However, the method proposed was to eliminate the letter from the character set entirely (thereby retaining 48 as the number of lexical characters, which the colon had increased to 49). This was considered beneficial in that it would promote structured programming, by making it impossible to use the notorious GO TO
statement as before. (Troublesome FORMAT
statements would also be eliminated.) It was noted that this "might invalidate some existing programs" but that most of these "probably were non-conforming, anyway".[25][26]
During the standards committee battle over whether the "minimum trip count" for the FORTRAN 77 DO
statement should be zero (allowing no execution of the block) or one (the "plunge-ahead" DO
), another facetious alternative was proposed (by Loren Meissner) to have the minimum trip be two—since there is no need for a loop if it is only executed once.
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