On 07/20/2010 07:06 PM, Ivan Maidanski wrote:
> Hello, Andrew!
>
>> On 06/29/2010 10:22 AM, Ivan Maidanski wrote:
>>> Hi!
>>>
>>> I've fixed a number of bugs in StrictMath class (the RI here is fdlibm of
>>> some version).
>>>
>>> ChangeLog entries:
>>>
>>> * java/lang/StrictMath.java:
>>> (acos(double)): Bug fix for x <= -1/2 case.
>>> (atan(double)): Fix documentation typo.
>>> (pow(double,double)): Fix a comment; put y == 1/2 case handling after
>>> x == -0 case (since pow(-0, 1/2) == 0 but sqrt(-0) == -0); return -0
>>> (or -INF) for pow(-0, 2*k) where k is non-zero integer; simplify
>>> expression for "negative" variable.
>>> (IEEEremainder(double,double)): Bug fix for x == -0 and x == -|y|
>>> cases; bug fix for |y| >= 2**-1021 and |x| > |y|/2.
>>> (remPiOver2(double[],double[],int,int)): Reset "recompute" at the
>>> beginning of every do/while iteration.
>>> (tan(double,double,boolean)): Negate the result if x <= -0.6744.
>>
>> Hi Ivan,
>>
>> Firstly please attach patches as type text; that way people can read
>> them in their mailers.
>
> I don't understand. I attach patches with .diff extension. Shall I use .txt?
I think they had a mime-type of application/binary.
>> Can you please send test cases that pass with this patch?
>
> Ok. I'll write them a bit later...
>
>>
>> diff -ru CVS/classpath/java/lang/StrictMath.java
>> updated/classpath/java/lang/StrictMath.java
>> --- CVS/classpath/java/lang/StrictMath.java 2010-06-29 10:11:06.000000000
>> +0400
>> +++ updated/classpath/java/lang/StrictMath.java 2010-06-29
>> 12:51:50.000000000 +0400
>> @@ -1,5 +1,6 @@
>> /* java.lang.StrictMath -- common mathematical functions, strict Java
>> - Copyright (C) 1998, 2001, 2002, 2003, 2006 Free Software Foundation, Inc.
>> + Copyright (C) 1998, 2001, 2002, 2003, 2006, 2010
>> + Free Software Foundation, Inc.
>>
>> This file is part of GNU Classpath.
>>
>> @@ -456,9 +457,10 @@
>> double r = x - (PI_L / 2 - x * (p / q));
>> return negative ? PI / 2 + r : PI / 2 - r;
>> }
>> + double z = (1 - x) * 0.5;
>> if (negative) // x<=-0.5.
>> {
>> - double z = (1 + x) * 0.5;
>> + // z = (1+orig_x)*0.5
>>
>> Please don't leave commented lines in code. If they're wrong, please
>> take them out.
>
> This is not a commented code - it's a reference C code from fdlibm. It might
> be better to use some words instead of a formular like "x is not modified in
> fdlibm unlike in this implementation so we use 1-x (where x==-orig_x) instead
> of 1+x".
>
>
>>
>> @@ -1554,10 +1553,18 @@
>> else if (yisint == 1)
>> ax = -ax;
>> }
>> + else
>> + {
>> + // Check for x == -0 with odd y.
>> + if (1 / x < 0
>>
>> Why use "1 / x < 0" ?
>
> What's else to use? The alternative is Double.doubleToRawLongBits(x)
> < 0 but (1/x)<0 is cheaper (recall that |x| is zero).
In
class T
{
boolean foo(double x)
{
return Double.doubleToRawLongBits(x) < 0;
}
boolean bar(double x)
{
return (1/x) < 0;
}
}
gcj gives you
T.foo(double)boolean:
movsd %xmm0, -16(%rsp)
movq -16(%rsp), %rax
shrq $63, %rax
ret
for the first, and
T.bar(double)boolean:
movsd .LC0(%rip), %xmm1
divsd %xmm0, %xmm1
movapd %xmm1, %xmm0
xorpd %xmm1, %xmm1
ucomisd %xmm0, %xmm1
seta %al
ret
for the second. Any JIT might do something similar.
IMO it's always better to say what you mean and let the optimizer
worry about optimization.
Andrew.
