Java调用LAPACK：从FORTRAN到Java的数值计算实践

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"这篇文档是关于JAVA调用LAPACK程序包的说明，详细阐述了如何将FORTRAN编写的高效线性代数运算库LAPACK转化为Java可用的类文件，使得Java程序员能够利用这些高性能的数值计算子程序。文档作者包括David M. Doolin、Jack Dongarra和Keith Seymour，他们分别来自加利福尼亚大学伯克利分校、橡树岭国家实验室和田纳西大学。JLAPACK项目的目标是通过专用的FORTRAN到Java的源码级编译器，将LAPACK的子程序转换为Java虚拟机（JVM）可执行的类文件，简化LAPACK的应用程序接口（API），以便更好地适应Java的面向对象设计。报告讨论了JLAPACK项目涉及的研究问题，以及当前的实现和状态。" 在Java中调用LAPACK程序包涉及到以下几个关键知识点： 1. **LAPACK库**：LAPACK是一个用于解决线性代数问题的FORTRAN77库，提供了一系列高效的算法，用于求解线性方程组、特征值问题、奇异值分解等。它是数值计算领域的标准库，广泛应用于科学计算和工程领域。 2. **JAVA与FORTRAN互操作**：由于LAPACK是用FORTRAN编写的，而Java是一种不同的编程语言，因此需要一种机制来实现它们之间的互操作。JLAPACK项目通过源码级编译器将FORTRAN源代码转换为Java类，使得Java应用可以直接调用LAPACK的子程序。 3. **JLAPACK项目**：该项目的主要目标是将LAPACK的功能引入Java世界，使得Java程序员可以利用FORTRAN库的强大计算能力，同时保持Java的可移植性和面向对象特性。这个过程包括了对LAPACK API的简化和调整，以适应Java的编程模型。 4. **源码级编译器**：为了实现FORTRAN到Java的转换，JLAPACK使用了一个特殊目的的编译器，它能将FORTRAN源代码转换成符合Java语法规则的类文件，这使得Java虚拟机可以理解和执行这些代码。 5. **面向对象的API设计**：在Java中，LAPACK的API被重新设计得更简洁，以充分利用Java的面向对象特性。这可能包括将原来的函数式接口转换为类和方法的形式，以及封装数据结构以减少冗余和提高代码可读性。 6. **性能考虑**：虽然Java的执行效率通常不如FORTRAN，但通过JLAPACK，Java应用程序能够直接调用优化过的LAPACK子程序，从而获得接近原生FORTRAN的速度。此外，Java的多线程能力还可以用于并行化计算，进一步提升性能。 7. **应用领域**：JLAPACK使得Java应用程序，尤其是那些需要进行大量数值计算的科学应用和Web应用程序，能够利用LAPACK的强大功能，无需依赖FORTRAN编译环境。该文档详细介绍了JLAPACK项目的技术实现和意义，为Java开发者提供了调用高性能线性代数计算的途径，促进了Java在科学计算领域的应用。

116 D.M. Doolin et al. / JLAPACK – compiling LAPACK FORTRAN to Java

code does not attempt to call Dummy.label() (in

the JVM, a zero byte corresponds to the nop instruc-

tion – i.e., it does nothing). On the second pass, we

scan for calls to Dummy.go_to(). For each call,

we look up the target label of the goto in the hash

table to obtain the actual bytecode address of the

label. Then we may replace the Dummy.go_to()

method invocation with an actual goto instruction.

Since the method invocation instruction sequence is

longer than the goto instruction, we zero out the re-

maining bytes.

So far, this method has been successful in translat-

ing GOTO statements in the BLAS/LAPACK source

code and testing routines. There may be some cases

in which “hacking” the compiler-producedbytecode as

we have done will produce unexpected results, possi-

bly putting the JVM into an unusual state. The Java

compiler generates code under certain assumptions,

one example of which is that the program should not

branch to a statement within a loop from outside the

loop. Our GOTO translation method has the poten-

tial to violate these assumptions, although we have not

yet come across a speciﬁc instance in the BLAS or

LAPACK source.

2.1.9. The need for code restructuring

Even though we now have a way to translate any ar-

bitrary GOTO statement into Java source, there is still

another problem caused by Java’s lack of a goto state-

ment. Consider the following segment of code from

ddot.f:

if(incx.eq.1.and.incy.eq.1)

go to 20

[...code for unequal

increments...]

ddot = dtemp

return

c code for both increments

equal to 1

20 m = mod(n,5)

The ﬁrst line of code checks whether both increments

are equal to 1 and if so, skips the section of code to deal

with unequal increments. We can see by looking at the

FORTRAN code (and so can the FORTRAN compiler)

that statement 20 can be reached. However, looking at

the Java source code produced by f2j, it is easy to see

why the Java compiler does not recognize that fact:

if (incx == 1 && incy == 1)

Dummy.go_to("Ddot",20);

[...code for unequal increments...]

ddot = dtemp;

return ddot;

Dummy.label("Ddot",20);

m = (n)%(5) ;

When the Java compiler analyzes this program, it

views the call to Dummy.go_to as a normal method

call. So, as far as javac is concerned, execution resumes

with the code immediately following the method call.

Since the segment of code following the method call

ends with a return statement, javac determines

that any statements following the return cannot be

reached. Normally this would be a perfectly reason-

able determination, but in this case we know that the

call to Dummy.go_to will really cause the program

to branch to statement 20.

Currently, there are a few ways to handle this. We

could manually change the FORTRAN source code

such that the IF expressionis reversed and put the equal

increments code ahead of the unequal increments code.

There are code restructuring tools that can recognize

and restructure these constructs automatically, remov-

ing the GOTO in the process. We could restructure the

Java source code after translation (not a great idea). Fu-

ture versions of f2j may have some code restructuring

ability built in, so that they can generate correct Java

source code without the need for manual restructuring

or external tools. Our current approach is to generate

one “real” return statement at the end of the function

or subroutine, with a unique label. All other return

statements are translated into dummy gotos, with the

target being the “real” return. Using this approach,

the java compiler views all return statements as func-

tion calls, so it no longer thinks that subsequent state-

ments cannot be reached. This approach is much sim-

pler and less error-prone than code restructuring.

2.1.10. DATA statements

FORTRAN DATA statements are generated as vari-

able declarations combined with initializations. They

must be combined since all variables are now gener-

ated as static class variables and therefore cannot have

separate assignment statements mixed in. For example,

the following DATA statement:

integer z(4)

DATA z/1,2,3,4/

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