Code review request for 6908131 Pure Java implementations of StrictMath.floor(double) &StrictMath.ceil(double)
Joseph D. Darcy
Joe.Darcy at Sun.COM
Tue Dec 15 19:16:34 UTC 2009
Dmitry Nadezhin wrote:
> > The current specification of the "interesting" methods in
> StrictMath, such as sin/cos, log, > etc. are to use the FDLIBM
> Thank you. I forgot about these lines in java.lang.StrictMath .
> As specification of java.lang.StrictMath is in terms of reference
> fdlibm C library
> and algorithms in new java.lang.StrictMath are expected similar to
> fdlibm algorithms,
> the task of formal verification becomes easier.
> The comment 3 in fdlibm's readme file warns about
> 3. Compiler failure on non-standard code
> Statements like
> *(1+(int*)&t1) = 0;
> are not standard C and cause some optimizing compilers (e.g. GCC)
> to generate bad code under optimization. These cases
> are to be addressed in the next release.
> Nevertheless, I hope that for some additional assumptions about C
> pointers, the meaning
> of fdlibm C code can be used as the specification.
The C language does not really define an operational semantics for these
operations. In contrast, with the tighter specification of Java's
integral and floating-point types and expressions using those values, it
is really well-posed to discuss the meaning of Java versions of these
> However, there is a question. Many methods of java.lang.StrictMath are
> used in a reference implementation of java.lang.Math methods.
> java.lang.Math specifies methods in terms of accuracy of the returned
> and monotonicity of the methods.
> Suppose that there is still a bug in fdlibm 5.3 and some fdlibm
> function fails to
> satisfy one ulp accuracy or monotonicity. What will be the
> specification of
> corresponding java.lang.StrictMath method in such a case ?
The FDLIBM functions are believed to follow the stated quality of
implementation criteria in java.lang.Math. When that turns out not to
be the case, there are a variety of remedies including fixing the bug in
FDLIBM. Fixing bugs I had independently found in pow and tan prompted
raising the required FDLIBM version from 5.2 to 5.3, see 5033578 "Java
should require use of latest fdlibm 5.3."
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