JDK-8302028: Port fdlibm atan2 to Java #12608

jddarcy · 2023-02-16T19:30:06Z

Working down the porting list, next stop, atan2.

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Issue

JDK-8302028: Port fdlibm atan2 to Java

Reviewers

Brian Burkhalter (@bplb - Reviewer)

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bridgekeeper · 2023-02-16T19:31:08Z

👋 Welcome back darcy! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2023-02-16T19:33:38Z

@jddarcy The following label will be automatically applied to this pull request:

core-libs

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jddarcy · 2023-02-16T19:35:07Z

Diffs of the various ports, starting with the original C vs the transliteration port:

$ diff -w Atan2.c Atan2.translit.java 
1c1,4
< /* __ieee754_atan2(y,x)
---
>     /**
>      * Returns the angle theta from the conversion of rectangular
>      * coordinates (x, y) to polar coordinates (r, theta).
>      *
27,34c30,31
< 
< #include "fdlibm.h"
< 
< #ifdef __STDC__
< static const double
< #else
< static double
< #endif
---
>     static class Atan2 {
>         private static final double
42,48c39
< #ifdef __STDC__
<         double __ieee754_atan2(double y, double x)
< #else
<         double __ieee754_atan2(y,x)
<         double  y,x;
< #endif
< {
---
>         static double compute(double y, double x) {
51c42
<         unsigned lx,ly;
---
>             /*unsigned*/ int lx,ly;
100c91
<         else z=atan(fabs(y/x));         /* safe to do y/x */
---
>             else z=atan(Math.abs(y/x));         /* safe to do y/x */
103c94,96
<             case 1: __HI(z) ^= 0x80000000;
---
>             case 1: 
>                 // original:__HI(z) ^= 0x80000000;
>                 z = __HI(z, __HI(x) ^ 0x80000000);
109a103
>     }

And the transliteration vs the more idiomatic port:

$ diff -w Atan2.translit.java Atan2.fdlibm.java 
30a31,32
>         private Atan2() {throw new UnsupportedOperationException();}
> 
33,37c35,37
<             zero  = 0.0,
<             pi_o_4  = 7.8539816339744827900E-01, /* 0x3FE921FB, 0x54442D18 */
<             pi_o_2  = 1.5707963267948965580E+00, /* 0x3FF921FB, 0x54442D18 */
<             pi      = 3.1415926535897931160E+00, /* 0x400921FB, 0x54442D18 */
<             pi_lo   = 1.2246467991473531772E-16; /* 0x3CA1A626, 0x33145C07 */
---
>             pi_o_4  = 0x1.921fb54442d18p-1,  // 7.8539816339744827900E-01
>             pi_o_2  = 0x1.921fb54442d18p0,   // 1.5707963267948965580E+00
>             pi_lo   = 0x1.1a62633145c07p-53; // 1.2246467991473531772E-16
44c44,45
<             hx = __HI(x); ix = hx&0x7fffffff;
---
>             hx = __HI(x);
>             ix = hx & 0x7fff_ffff;
46c47,48
<             hy = __HI(y); iy = hy&0x7fffffff;
---
>             hy = __HI(y);
>             iy = hy&0x7fff_ffff;
48,49c50,51
<             if(((ix|((lx|-lx)>>31))>0x7ff00000)||
<                ((iy|((ly|-ly)>>31))>0x7ff00000))    /* x or y is NaN */
---
>             if (((ix | ((lx | -lx) >> 31)) > 0x7ff0_0000)||
>                 ((iy |((ly | - ly) >> 31)) > 0x7ff0_0000))    // x or y is NaN
51,52c53,55
<             if(((hx-0x3ff00000)|lx)==0) return atan(y);   /* x=1.0 */
<             m = ((hy>>31)&1)|((hx>>30)&2);  /* 2*sign(x)+sign(y) */
---
>             if (((hx - 0x3ff0_0000) | lx) == 0) // x = 1.0
>                 return StrictMath.atan(y);
>             m = ((hy >> 31) & 1)|((hx >> 30) & 2);  // 2*sign(x) + sign(y)
54c57
<             /* when y = 0 */
---
>             // when y = 0
56,73c59,67
<                 switch(m) {
<                 case 0:
<                 case 1: return y;       /* atan(+-0,+anything)=+-0 */
<                 case 2: return  pi+tiny;/* atan(+0,-anything) = pi */
<                 case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */
<                 }
<             }
<             /* when x = 0 */
<             if((ix|lx)==0) return (hy<0)?  -pi_o_2-tiny: pi_o_2+tiny;
< 
<             /* when x is INF */
<             if(ix==0x7ff00000) {
<                 if(iy==0x7ff00000) {
<                     switch(m) {
<                     case 0: return  pi_o_4+tiny;/* atan(+INF,+INF) */
<                     case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */
<                     case 2: return  3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/
<                     case 3: return -3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/
---
>                 return switch(m) {
>                 case 0, 1 ->  y;              // atan(+/-0, +anything)  = +/-0
>                 case 2    ->  Math.PI + tiny; // atan(+0,   -anything)  =  pi
>                 default   -> -Math.PI - tiny; // atan(-0,   -anything)  = -pi
>                 };
>             }
>             // when x = 0
>             if ((ix | lx) == 0) {
>                 return (hy < 0)?  -pi_o_2 - tiny : pi_o_2 + tiny;
74a69,78
> 
>             // when x is INF
>             if (ix == 0x7ff0_0000) {
>                 if (iy == 0x7ff0_0000) {
>                     return switch(m) {
>                     case 0  ->  pi_o_4 + tiny;      // atan(+INF, +INF)
>                     case 1  -> -pi_o_4 - tiny;      // atan(-INF, +INF)
>                     case 2  ->  3.0*pi_o_4 + tiny;  // atan(+INF, -INF)
>                     default -> -3.0*pi_o_4 - tiny;  // atan(-INF, -INF)
>                     };
76,80c80,85
<                     switch(m) {
<                     case 0: return  zero  ;     /* atan(+...,+INF) */
<                     case 1: return -1.0*zero  ; /* atan(-...,+INF) */
<                     case 2: return  pi+tiny  ;  /* atan(+...,-INF) */
<                     case 3: return -pi-tiny  ;  /* atan(-...,-INF) */
---
>                     return switch(m) {
>                     case 0  ->  0.0;                // atan(+..., +INF)
>                     case 1  -> -0.0;                // atan(-..., +INF)
>                     case 2  ->  Math.PI + tiny;     // atan(+..., -INF)
>                     default -> -Math.PI - tiny;     // atan(-..., -INF)
>                     };
82a88,90
>             // when y is INF
>             if (iy == 0x7ff0_0000) {
>                 return (hy < 0)? -pi_o_2 - tiny : pi_o_2 + tiny;
84,85d91
<             /* when y is INF */
<             if(iy==0x7ff00000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny;
87c93
<             /* compute y/x */
---
>             // compute y/x
89,101c95,107
<             if(k > 60) z=pi_o_2+0.5*pi_lo;  /* |y/x| >  2**60 */
<             else if(hx<0&&k<-60) z=0.0;     /* |y|/x < -2**60 */
<             else z=atan(Math.abs(y/x));         /* safe to do y/x */
<             switch (m) {
<             case 0: return       z  ;   /* atan(+,+) */
<             case 1: 
<                 // original:__HI(z) ^= 0x80000000;
<                 z = __HI(z, __HI(x) ^ 0x80000000);
<                 return       z  ;   /* atan(-,+) */
<             case 2: return  pi-(z-pi_lo);/* atan(+,-) */
<             default: /* case 3 */
<                 return  (z-pi_lo)-pi;/* atan(-,-) */
<             }
---
>             if (k > 60) {   // |y/x| >  2**60
>                 z = pi_o_2+0.5*pi_lo;
>             } else if (hx < 0 && k < -60) { // |y|/x < -2**60
>                 z = 0.0;
>             } else { // safe to do y/x
>                 z = StrictMath.atan(Math.abs(y/x));
>             }
>             return switch (m) {
>             case 0  ->  z;                    // atan(+, +)
>             case 1  -> -z;                    // atan(-, +)
>             case 2  -> Math.PI - (z - pi_lo); // atan(+, -)
>             default -> (z - pi_lo) - Math.PI; // atan(-, -), case 3
>             };

A few notes: I decided to use expression switches, but that is not necessary. Also, in the final switch I used "-z" as a more direct idiom to negate z than the form in the original fdlibm.

mlbridge · 2023-02-16T19:38:02Z

Webrevs

bplb · 2023-02-16T21:51:38Z

The port looks reasonable to me.

rgiulietti · 2023-02-17T13:32:34Z

test/jdk/java/lang/StrictMath/FdlibmTranslit.java

+            hy = __HI(y); iy = hy&0x7fffffff;
+            ly = __LO(y);
+            if(((ix|((lx|-lx)>>31))>0x7ff00000)||
+               ((iy|((ly|-ly)>>31))>0x7ff00000))    /* x or y is NaN */


I think that >>31 must be replaced by >>>31.

test/jdk/java/lang/StrictMath/FdlibmTranslit.java

rgiulietti · 2023-02-17T13:50:17Z

src/java.base/share/classes/java/lang/FdLibm.java

+            iy = hy&0x7fff_ffff;
+            ly = __LO(y);
+            if (((ix | ((lx | -lx) >> 31)) > 0x7ff0_0000)||
+                ((iy |((ly | - ly) >> 31)) > 0x7ff0_0000))    // x or y is NaN


I think that >> 31 must be replaced by >>> 31.

Well spotted; corrected the code and added additional tests to catch that case. Thanks.

Well spotted; corrected the code and added additional tests to catch that case. Thanks.

PS From some quick manual inspections, the other recent ports of FDLIBM methods don't look vulnerable to this kind of problem. However, as follow-up work later in 21 I'll implement: JDK-8302800: Augment NaN handling tests of FDLIBM methods.

rgiulietti · 2023-02-17T14:02:35Z

src/java.base/share/classes/java/lang/FdLibm.java

+                return switch(m) {
+                case 0, 1 ->  y;              // atan(+/-0, +anything)  = +/-0
+                case 2    ->  Math.PI + tiny; // atan(+0,   -anything)  =  pi
+                default   -> -Math.PI - tiny; // atan(-0,   -anything)  = -pi


The original switch statement and this switch expression are semantically equivalent only because of our knowledge that m can only assume values 0, 1, 2, or 3. This requires more reasoning than a more verbatim copy of the original statement. Not sure if it is worth.

The same holds for the switch expressions below.

Yes, the use of switch expressions here is certainly not strictly necessary.

Something that helped convince me it was okay was that the final switch on m in atan2 uses the set of case labels {0, 1, 2, default}., further implying that m can only take on the values {0, 1, 2, 3}.

Reverted to switch statements rather than switch expressions.

test/jdk/java/lang/Math/Atan2Tests.java

bplb

Looks good.

openjdk · 2023-02-22T21:57:45Z

@jddarcy This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8302028: Port fdlibm atan2 to Java

Reviewed-by: bpb

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 33 new commits pushed to the master branch:

07e976a: 8303081: Serial: Remove unused VM_MarkSweep
8de841d: 8302667: Improve message format when failing to load symbols or libraries
f893d23: 8303024: (fs) WindowsFileSystem.supportedFileAttributeViews can use Set.of
d7ada66: 8303084: G1 Heap region liveness verification has inverted return value
5d7e7e2: 8302760: Improve liveness/remembered set verification for G1
b0e0f37: 8303067: G1: Remove unimplemented G1FullGCScope::heap_transition
1a62a12: 8302880: Fix includes in g1ConcurrentMarkObjArrayProcessor files
ee37af4: 8302975: Remove redundant mark verification during G1 Full GC
83bea26: 8300575: JVMTI support when using alternative virtual thread implementation
25bfed3: 8302979: (fs) Files usage of SUPPORTED_CHARSETS could be simplified
... and 23 more: https://git.openjdk.org/jdk/compare/dfce4e1943f2f95b74b5a9cdde9d738dcffd0b43...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

jddarcy · 2023-02-22T22:08:22Z

/integrate

jddarcy · 2023-02-22T22:23:25Z

/integrate

openjdk · 2023-02-22T22:51:03Z

Going to push as commit fcaf871.
Since your change was applied there have been 33 commits pushed to the master branch:

07e976a: 8303081: Serial: Remove unused VM_MarkSweep
8de841d: 8302667: Improve message format when failing to load symbols or libraries
f893d23: 8303024: (fs) WindowsFileSystem.supportedFileAttributeViews can use Set.of
d7ada66: 8303084: G1 Heap region liveness verification has inverted return value
5d7e7e2: 8302760: Improve liveness/remembered set verification for G1
b0e0f37: 8303067: G1: Remove unimplemented G1FullGCScope::heap_transition
1a62a12: 8302880: Fix includes in g1ConcurrentMarkObjArrayProcessor files
ee37af4: 8302975: Remove redundant mark verification during G1 Full GC
83bea26: 8300575: JVMTI support when using alternative virtual thread implementation
25bfed3: 8302979: (fs) Files usage of SUPPORTED_CHARSETS could be simplified
... and 23 more: https://git.openjdk.org/jdk/compare/dfce4e1943f2f95b74b5a9cdde9d738dcffd0b43...master

Your commit was automatically rebased without conflicts.

openjdk · 2023-02-22T22:52:15Z

@jddarcy Pushed as commit fcaf871.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

openjdk · 2023-02-22T23:03:16Z

@jddarcy The command integrate can only be used in open pull requests.

JDK-8302028: Port fdlibm atan2 to Java

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openjdk bot added the rfr Pull request is ready for review label Feb 16, 2023

openjdk bot added the core-libs core-libs-dev@openjdk.org label Feb 16, 2023

jddarcy added 2 commits February 16, 2023 19:32

Merge branch 'master' into JDK-8302028

d0aad55

Update regression test.

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rgiulietti reviewed Feb 17, 2023

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Correct and test for issue found in code review.

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jddarcy mentioned this pull request Feb 19, 2023

JDK-8302800: Augment NaN handling tests of FDLIBM methods #12644

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jddarcy added 3 commits February 21, 2023 10:33

Merge branch 'master' into JDK-8302028

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Use NaN regression test infrastructure.

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Respond to review feedback.

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bplb approved these changes Feb 22, 2023

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jddarcy deleted the JDK-8302028 branch October 26, 2024 19:26

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JDK-8302028: Port fdlibm atan2 to Java #12608

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JDK-8302028: Port fdlibm atan2 to Java #12608

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