?? csdn_文檔中心_新的c語言：一切都源于fortran.htm
字號:
<P class=MsoNormal style="TEXT-INDENT: 21pt"><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">這兩種不同的參數傳遞機制是任何程序設計語言定義者所必須面對的不一致性的代表。語言需要特殊的實現實現技術嗎？也許這將會以付出效率為代價？語言的特性是否應該為了避免爭議而改變？</SPAN><SPAN
lang=EN-US>FORTRAN</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">的定義者因為效率而允許同時存在兩種參數傳遞機制。而一旦這樣的決定做了出來，某種類型的程序就變的不一致了，并將導致無法定義的結果（</SPAN><SPAN
lang=EN-US>outlawed</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">）。</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 21pt"><SPAN
lang=EN-US> <o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 21pt"><SPAN
lang=EN-US>FORTRAN 66 </SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">標準包含了一系列可能會誤導程序員的規則。在函數參數列表中，對于任何變量你都只能傳遞一次。如果你傳遞了一個變量作為函數參數，那么這個函數就不能再在全局上引用這個變量</SPAN><SPAN
lang=EN-US>(FORTRAN <B>COMMON</B>)</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">。如果你傳遞給一個變量給函數，你就不能再傳遞任何東西，并且這個函數也不能再引用任何東西，</SPAN><SPAN
lang=EN-US>that overlaps it in storage (FORTRAN
<B>EQUIVALENCE</B>)</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">。在這樣的規則下，沒有什么程序可以確定應該采用何種參數傳遞機制。</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 21pt"><SPAN
lang=EN-US> <o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 21pt"><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">大約十年以后</SPAN><SPAN
lang=EN-US>[</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">譯注：意指</SPAN><SPAN
lang=EN-US>1970s]</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">，為了實現超級計算機</SPAN><SPAN
lang=EN-US>Cray 1</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">的高性能，超級計算機需要高優化的編譯器來使傳統的程序能夠使用機器的向量寄存器（</SPAN><SPAN
lang=EN-US>vector registers</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">）。考慮</SPAN><SPAN
lang=EN-US>Example 5</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">中的程序。其中對于函數來說最有效率的代碼就是先后把數組指針</SPAN><SPAN
lang=EN-US>x</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">，</SPAN><SPAN
lang=EN-US>y</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">載入到向量寄存器中然后執行向量加指令來把兩個向量寄存器中的變量加在一起。如果編譯器以產生向量指令的方式來取代傳統的使用循環來訪問數組中的每一個元素的方式，那么代碼的運行效率將得到巨大的提升。</SPAN></P>
<P class=MsoNormal
style="TEXT-INDENT: 31.5pt; mso-char-indent-count: 3.0; mso-char-indent-size: 10.5pt"><I><SPAN
lang=EN-US>Example 5:</SPAN></I><SPAN lang=EN-US
style="mso-font-kerning: 0pt"><o:p></o:p></SPAN></P><PRE style="MARGIN: 0cm 36pt 0pt"><SPAN lang=EN-US>void</SPAN></PRE><PRE style="MARGIN: 0cm 36pt 0pt"><SPAN lang=EN-US>vector_add(float *x, float *y,</SPAN></PRE><PRE style="MARGIN: 0cm 36pt 0pt"><SPAN lang=EN-US><SPAN style="mso-spacerun: yes"> </SPAN>float *result)</SPAN></PRE><PRE style="MARGIN: 0cm 36pt 0pt"><SPAN lang=EN-US><SPAN style="mso-spacerun: yes"> </SPAN>{</SPAN></PRE><PRE style="MARGIN: 0cm 36pt 0pt"><SPAN lang=EN-US><SPAN style="mso-spacerun: yes"> </SPAN>int i;</SPAN></PRE><PRE style="MARGIN: 0cm 36pt 0pt"><SPAN lang=EN-US><SPAN style="mso-spacerun: yes"> </SPAN>for (i = 0; i < 64; ++i)</SPAN></PRE><PRE style="MARGIN: 0cm 36pt 0pt"><SPAN lang=EN-US><SPAN style="mso-spacerun: yes"> </SPAN>result[i] = x[i] + y[i];</SPAN></PRE><PRE style="MARGIN: 0cm 36pt 0pt"><SPAN lang=EN-US><SPAN style="mso-spacerun: yes"> </SPAN>}</SPAN></PRE>
<P class=MsoNormal style="TEXT-INDENT: 21pt"><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">編譯器中的優化器肯定會把循環轉化成一系列的向量指令，但是問題在于那些向量指令是否真的</SPAN><SPAN
lang=EN-US>whether the sequence of vector instructions is really
equivalent to the original loop</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">。你能在處理</SPAN><SPAN
lang=EN-US>result</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">數組的存儲工作之前就把</SPAN><SPAN
lang=EN-US>x,y</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">數組載入到向量寄存器中，只因為你清楚</SPAN><SPAN
lang=EN-US>result</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">數組和</SPAN><SPAN
lang=EN-US>x,y</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">數組都是不同的個體。考慮如果</SPAN><SPAN
lang=EN-US>result</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">指向</SPAN><SPAN
lang=EN-US>x[1]</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">，將會發生什么？在這種情況下</SPAN><SPAN
lang=EN-US>result[0]</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">其實就是</SPAN><SPAN
lang=EN-US>x[1]</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">，同樣</SPAN><SPAN
lang=EN-US>result[I]</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">其實就是</SPAN><SPAN
lang=EN-US>x[I+1],</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">每一次循環迭代過程中都會存儲下一次的迭代中會被引用的變量。如果在做</SPAN><SPAN
lang=EN-US>result</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">的存儲工作之前就把</SPAN><SPAN
lang=EN-US>x</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">載入到向量寄存器中去，變量值將會改變</SPAN><SPAN
lang=EN-US>calculated change</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">。正是在這一點上，</SPAN><SPAN
lang=EN-US>FORTRAN</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">的定義就帶來了沖突。為了避免在傳遞機制中需要引入一個特殊的參數，</SPAN><SPAN
lang=EN-US>FORTRAN</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">標準定義了一系列精確的規則用來允許向量化編譯器（</SPAN><SPAN
lang=EN-US>vectorizing compiler</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">）假設</SPAN><SPAN
lang=EN-US>x,y</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">和</SPAN><SPAN
lang=EN-US>result</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">都是互不相關的，</SPAN><SPAN
lang=EN-US>non-overlapping arrays</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">。就這樣偶然的，</SPAN><SPAN
lang=EN-US>FORTRAN</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">在向量機上就有了巨大的性能優勢。</SPAN></P>
<P class=MsoPlainText style="TEXT-INDENT: 18pt"></SPAN><SPAN
lang=EN-US
style="FONT-SIZE: 14pt; mso-bidi-font-size: 10.5pt; mso-hansi-font-family: 宋體; mso-bidi-font-family: 宋體"><o:p></o:p></SPAN> </P>
<P class=MsoPlainText style="TEXT-INDENT: 18pt"><SPAN lang=EN-US
style="FONT-SIZE: 9pt; mso-bidi-font-size: 10.5pt; mso-hansi-font-family: 宋體; mso-bidi-font-family: 宋體"> <o:p></o:p></SPAN></P><BR></TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE><BR>
<TABLE align=center bgColor=#006699 border=0 cellPadding=0 cellSpacing=0
width=770>
<TBODY>
<TR bgColor=#006699>
<TD align=middle bgColor=#006699 id=white><FONT
color=#ffffff>對該文的評論</FONT></TD>
<TD align=middle>
<SCRIPT src="CSDN_文檔中心_新的C語言：一切都源于FORTRAN.files/readnum.htm"></SCRIPT>
</TD></TR></TBODY></TABLE>
<TABLE align=center bgColor=#666666 border=0 cellPadding=2 cellSpacing=1
width=770>
<TBODY>
<TR>
<TD bgColor=#cccccc colSpan=3><SPAN style="COLOR: #cccccc"><IMG height=16
hspace=1 src="CSDN_文檔中心_新的C語言：一切都源于FORTRAN.files/ico_pencil.gif" width=16>
</SPAN> husz2001 <I>(2003-11-7 15:31:07)</I>
</TD></TR>
<TR>
<TD bgColor=#ffffff colSpan=3 width=532><BR>老實說,看的不太懂.不知道,有什么意義.
<BR></TD></TR></TBODY></TABLE>
<TABLE align=center bgColor=#666666 border=0 cellPadding=2 cellSpacing=1
width=770>
<TBODY>
<TR>
<TD bgColor=#cccccc colSpan=3><SPAN style="COLOR: #cccccc"><IMG height=16
hspace=1 src="CSDN_文檔中心_新的C語言：一切都源于FORTRAN.files/ico_pencil.gif" width=16>
</SPAN> whyNotHere <I>(2003-10-8 11:16:51)</I>
</TD></TR>
<TR>
<TD bgColor=#ffffff colSpan=3 width=532><BR>c語言是用得最爽的語言。 簡單易用，又功能強大。
<BR></TD></TR></TBODY></TABLE>
<TABLE align=center bgColor=#666666 border=0 cellPadding=2 cellSpacing=1
width=770>
<TBODY>
<TR>
<TD bgColor=#cccccc colSpan=3><SPAN style="COLOR: #cccccc"><IMG height=16
hspace=1 src="CSDN_文檔中心_新的C語言：一切都源于FORTRAN.files/ico_pencil.gif" width=16>
</SPAN> MatrixCpp <I>(2003-10-7 18:10:57)</I>
</TD></TR>
<TR>
<TD bgColor=#ffffff colSpan=3 width=532><BR>樓下的這樣的行為好象不是很妥啊。
<BR></TD></TR></TBODY></TABLE>
<TABLE align=center bgColor=#666666 border=0 cellPadding=2 cellSpacing=1
width=770>
<TBODY>
<TR>
<TD bgColor=#cccccc colSpan=3><SPAN style="COLOR: #cccccc"><IMG height=16
hspace=1 src="CSDN_文檔中心_新的C語言：一切都源于FORTRAN.files/ico_pencil.gif" width=16>
</SPAN> codecopier <I>(2003-10-6 22:54:45)</I>
</TD></TR>
<TR>
<TD bgColor=#ffffff colSpan=3 width=532><BR>This performance advantage
also carried over into parallel processor machines. The goal for an
optimizing compiler for a parallel processor is to divide a loop into
several ranges of iterations that can be done by separate processors
working independently of each other. Thus, the loop in vector_add might be
divided into two ranges: one processor might handle iterations 0 to 31
while another processor simultaneously does iterations 32 to 63. Work can
be divided up among different processors only if the compiler knows that
the results of the iterations done by one processor are not needed by a
different processor working simultaneously. Proving this usually means the
compiler needs to determine that different arrays are distinct,
non-overlapping objects. Again, the rules in FORTRAN are exactly what a
compiler needs in order to prove it can automatically parallelize a
program. While the FORTRAN performance advantage started out on
?? 快捷鍵說明
復制代碼
Ctrl + C
搜索代碼
Ctrl + F
全屏模式
F11
切換主題
Ctrl + Shift + D
顯示快捷鍵
?
增大字號
Ctrl + =
減小字號
Ctrl + -