JDK-8301396: Port fdlibm expm1 to Java

[jddarcy]

Next on the FDLIBM C -> Java port, expm1.
Coming soon, hyperbolic transcendentals (sinh, cosh, tanh)!

For expm1, the C vs transliteration port show the usual kind of differences, beside formatting of the constants, the use of the __HI macro on the left-hand side needs to be replaced by a method call and an assignment, as seen below:

< 
< #include "fdlibm.h"
< 
< #ifdef __STDC__
< static const double
< #else
< static double
< #endif
< one             = 1.0,
< huge            = 1.0e+300,
< tiny            = 1.0e-300,
< o_threshold     = 7.09782712893383973096e+02,/* 0x40862E42, 0xFEFA39EF */
< ln2_hi          = 6.93147180369123816490e-01,/* 0x3fe62e42, 0xfee00000 */
< ln2_lo          = 1.90821492927058770002e-10,/* 0x3dea39ef, 0x35793c76 */
< invln2          = 1.44269504088896338700e+00,/* 0x3ff71547, 0x652b82fe */
---
>     static class Expm1 {
>         private static final double one             = 1.0;
>         private static final double huge            = 1.0e+300;
>         private static final double tiny            = 1.0e-300;
>         private static final double o_threshold     = 7.09782712893383973096e+02; /* 0x40862E42, 0xFEFA39EF */
>         private static final double ln2_hi          = 6.93147180369123816490e-01; /* 0x3fe62e42, 0xfee00000 */
>         private static final double ln2_lo          = 1.90821492927058770002e-10; /* 0x3dea39ef, 0x35793c76 */
>         private static final double invln2          = 1.44269504088896338700e+00; /* 0x3ff71547, 0x652b82fe */
111,115c104,108
< Q1  =  -3.33333333333331316428e-02, /* BFA11111 111110F4 */
< Q2  =   1.58730158725481460165e-03, /* 3F5A01A0 19FE5585 */
< Q3  =  -7.93650757867487942473e-05, /* BF14CE19 9EAADBB7 */
< Q4  =   4.00821782732936239552e-06, /* 3ED0CFCA 86E65239 */
< Q5  =  -2.01099218183624371326e-07; /* BE8AFDB7 6E09C32D */
---
>         private static final double Q1  =  -3.33333333333331316428e-02; /* BFA11111 111110F4 */
>         private static final double Q2  =   1.58730158725481460165e-03; /* 3F5A01A0 19FE5585 */
>         private static final double Q3  =  -7.93650757867487942473e-05; /* BF14CE19 9EAADBB7 */
>         private static final double Q4  =   4.00821782732936239552e-06; /* 3ED0CFCA 86E65239 */
>         private static final double Q5  =  -2.01099218183624371326e-07; /* BE8AFDB7 6E09C32D */
117,123c110
< #ifdef __STDC__
<         double expm1(double x)
< #else
<         double expm1(x)
<         double x;
< #endif
< {
---
>         static double compute(double x) {
126c113
<         unsigned hx;
---
>             /*unsigned*/ int hx;
157c144
<                 k  = invln2*x+((xsb==0)?0.5:-0.5);
---
>                     k  = (int)(invln2*x+((xsb==0)?0.5:-0.5));
188c175
<                 __HI(y) += (k<<20);     /* add k to y's exponent */
---
>                     y = __HI(y,  __HI(y) + (k<<20));     /* add k to y's exponent */
193c180
<                 __HI(t) = 0x3ff00000 - (0x200000>>k);  /* t=1-2^-k */
---
>                     t = __HI(t, 0x3ff00000 - (0x200000>>k));  /* t=1-2^-k */
195c182
<                 __HI(y) += (k<<20);     /* add k to y's exponent */
---
>                     y = __HI(y, __HI(y) + (k<<20));     /* add k to y's exponent */
197c184
<                 __HI(t)  = ((0x3ff-k)<<20);     /* 2^-k */
---
>                     t = __HI(t, ((0x3ff-k)<<20));     /* 2^-k */
200c187
<                 __HI(y) += (k<<20);     /* add k to y's exponent */
---
>                     y = __HI(y, __HI(y) + (k<<20));     /* add k to y's exponent */
205c192
< 
---
>     }

When comparing the transliteration port and the more idiomatic port, there were no surprising or notable differences:

$ diff -w Expm1.translit.java Expm1.fdlibm.java  
99,102c99,102
<         private static final double o_threshold     = 7.09782712893383973096e+02; /* 0x40862E42, 0xFEFA39EF */
<         private static final double ln2_hi          = 6.93147180369123816490e-01; /* 0x3fe62e42, 0xfee00000 */
<         private static final double ln2_lo          = 1.90821492927058770002e-10; /* 0x3dea39ef, 0x35793c76 */
<         private static final double invln2          = 1.44269504088896338700e+00; /* 0x3ff71547, 0x652b82fe */
---
>         private static final double o_threshold =  0x1.62e42fefa39efp9;   //  7.09782712893383973096e+02
>         private static final double ln2_hi      =  0x1.62e42feep-1;       //  6.93147180369123816490e-01
>         private static final double ln2_lo      =  0x1.a39ef35793c76p-33; //  1.90821492927058770002e-10
>         private static final double invln2      =  0x1.71547652b82fep0;   //  1.44269504088896338700e+00
104,108c104,108
<         private static final double Q1  =  -3.33333333333331316428e-02; /* BFA11111 111110F4 */
<         private static final double Q2  =   1.58730158725481460165e-03; /* 3F5A01A0 19FE5585 */
<         private static final double Q3  =  -7.93650757867487942473e-05; /* BF14CE19 9EAADBB7 */
<         private static final double Q4  =   4.00821782732936239552e-06; /* 3ED0CFCA 86E65239 */
<         private static final double Q5  =  -2.01099218183624371326e-07; /* BE8AFDB7 6E09C32D */
---
>         private static final double Q1          = -0x1.11111111110f4p-5;  // -3.33333333333331316428e-02
>         private static final double Q2          =  0x1.a01a019fe5585p-10; //  1.58730158725481460165e-03
>         private static final double Q3          = -0x1.4ce199eaadbb7p-14; // -7.93650757867487942473e-05
>         private static final double Q4          =  0x1.0cfca86e65239p-18; //  4.00821782732936239552e-06
>         private static final double Q5          = -0x1.afdb76e09c32dp-23; // -2.01099218183624371326e-07
116,118c116,118
<             xsb = hx&0x80000000;            /* sign bit of x */
<             if(xsb==0) y=x; else y= -x;     /* y = |x| */
<             hx &= 0x7fffffff;               /* high word of |x| */
---
>             xsb = hx & 0x8000_0000;            /* sign bit of x */
>             y = Math.abs(x);
>             hx &= 0x7fff_ffff;               /* high word of |x| */
121,124c121,124
<             if(hx >= 0x4043687A) {                  /* if |x|>=56*ln2 */
<                 if(hx >= 0x40862E42) {              /* if |x|>=709.78... */
<                     if(hx>=0x7ff00000) {
<                         if(((hx&0xfffff)|__LO(x))!=0)
---
>             if (hx >= 0x4043_687A) {                  /* if |x| >= 56*ln2 */
>                 if (hx >= 0x4086_2E42) {              /* if |x| >= 709.78... */
>                     if (hx >= 0x7ff_00000) {
>                         if (((hx & 0xf_ffff) | __LO(x)) != 0) {
126c126,131
<                         else return (xsb==0)? x:-1.0;/* exp(+-inf)={inf,-1} */
---
>                         } else {
>                             return (xsb == 0)? x : -1.0; /* exp(+-inf)={inf,-1} */
>                         }
>                     }
>                     if (x > o_threshold) {
>                         return huge*huge; /* overflow */
128d132
<                     if(x > o_threshold) return huge*huge; /* overflow */
131c135
<                     if(x+tiny<0.0)          /* raise inexact */
---
>                     if (x + tiny < 0.0) {         /* raise inexact */
134a139
>             }
137,142c142,152
<             if(hx > 0x3fd62e42) {           /* if  |x| > 0.5 ln2 */
<                 if(hx < 0x3FF0A2B2) {       /* and |x| < 1.5 ln2 */
<                     if(xsb==0)
<                         {hi = x - ln2_hi; lo =  ln2_lo;  k =  1;}
<                     else
<                         {hi = x + ln2_hi; lo = -ln2_lo;  k = -1;}
---
>             if (hx > 0x3fd6_2e42) {           /* if  |x| > 0.5 ln2 */
>                 if (hx < 0x3FF0_A2B2) {       /* and |x| < 1.5 ln2 */
>                     if (xsb == 0) {
>                         hi = x - ln2_hi;
>                         lo =  ln2_lo;
>                         k =  1;}
>                     else {
>                         hi = x + ln2_hi;
>                         lo = -ln2_lo;
>                         k = -1;
>                     }
151,152c161
<             }
<             else if(hx < 0x3c900000) {      /* when |x|<2**-54, return x */
---
>             } else if (hx < 0x3c90_0000) {      /* when |x|<2**-54, return x */
154a164,165
>             } else {
>                 k = 0;
156d166
<             else k = 0;
164,165c174,176
<             if(k==0) return x - (x*e-hxs);          /* c is 0 */
<             else {
---
>             if (k == 0) {
>                 return x - (x*e - hxs);          /* c is 0 */
>             } else {
168c179,181
<                 if(k== -1) return 0.5*(x-e)-0.5;
---
>                 if (k == -1) {
>                     return 0.5*(x - e) - 0.5;
>                 }
170,171c183,187
<                     if(x < -0.25) return -2.0*(e-(x+0.5));
<                     else          return  one+2.0*(x-e);
---
>                     if(x < -0.25) {
>                         return -2.0*(e - (x + 0.5));
>                     } else {
>                         return  one + 2.0*(x - e);
>                     }
180c196
<                     t = __HI(t, 0x3ff00000 - (0x200000>>k));  /* t=1-2^-k */
---
>                     t = __HI(t, 0x3ff0_0000 - (0x2_00000 >> k));  /* t=1-2^-k */

---

Progress

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Issue

• JDK-8301396: Port fdlibm expm1 to Java

Reviewers

• Brian Burkhalter (@bplb - Reviewer)

Reviewing

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[bridgekeeper]

👋 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]

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

• core-libs

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[mlbridge]

Webrevs

• 01: Full - Incremental (5c065d3d)
• 00: Full (203092fe)

[turbanoff]

Suggested change

	x = Math.nextDown(Double.MIN_NORMAL);
	x = Math.nextDown(Double.MIN_NORMAL);

[turbanoff]

Suggested change

	lo = ln2_lo;
	lo = ln2_lo;

[turbanoff]

Suggested change

	k = 1;}
	k = 1;
	}

[turbanoff]

Suggested change

	if(x < -0.25) {
	if (x < -0.25) {

[turbanoff]

Suggested change

	return one + 2.0*(x - e);
	return one + 2.0*(x - e);

[turbanoff]

let's align this variable too

Suggested change

	y = Math.abs(x);
	y = Math.abs(x);

[turbanoff]

Suggested change

	x = hi - lo;
	x = hi - lo;

[jddarcy]

Thanks for the close reading; pushed those suggestions along with some others.

[rgiulietti]

With the corrections by @turbanoff LGTM.

[bplb]

Looks fine.

[openjdk]

@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:

8301396: Port fdlibm expm1 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 18 new commits pushed to the master branch:

• 3be5317: 8301798: [BACKOUT] jdb ThreadStartRequest and ThreadDeathRequest should use SUSPEND_NONE instead of SUSPEND_ALL
• e7247b1: 8298872: Update CheckStatus.java for changes to TLS implementation
• 20579e4: 8299994: java/security/Policy/Root/Root.java fails when home directory is read-only
• 5962226: 8300891: Deprecate for removal javax.swing.plaf.synth.SynthLookAndFeel.load(URL url)
• 8b70256: 8301787: java/net/httpclient/SpecialHeadersTest failing after JDK-8301306
• bccd55b: 8300295: [AIX] TestDaemonDestroy fails due to !is_primordial_thread assertion
• 7435b27: 8301744: Remove unused includes of genOopClosures.hpp
• 6f9106e: 8301306: java/net/httpclient/* fail with -Xcomp
• ac9e046: 8301479: Replace NULL with nullptr in os/linux
• cf68d9f: 8299155: C2: SubTypeCheckNode::verify() should not produce dependencies / oop pool entries
• ... and 8 more: https://git.openjdk.org/jdk/compare/ee0f5b5ed0f8f081c5e61e2083c31863cbf14fd2...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]

/integrate

[openjdk]

Going to push as commit 3449324.
Since your change was applied there have been 18 commits pushed to the master branch:

• 3be5317: 8301798: [BACKOUT] jdb ThreadStartRequest and ThreadDeathRequest should use SUSPEND_NONE instead of SUSPEND_ALL
• e7247b1: 8298872: Update CheckStatus.java for changes to TLS implementation
• 20579e4: 8299994: java/security/Policy/Root/Root.java fails when home directory is read-only
• 5962226: 8300891: Deprecate for removal javax.swing.plaf.synth.SynthLookAndFeel.load(URL url)
• 8b70256: 8301787: java/net/httpclient/SpecialHeadersTest failing after JDK-8301306
• bccd55b: 8300295: [AIX] TestDaemonDestroy fails due to !is_primordial_thread assertion
• 7435b27: 8301744: Remove unused includes of genOopClosures.hpp
• 6f9106e: 8301306: java/net/httpclient/* fail with -Xcomp
• ac9e046: 8301479: Replace NULL with nullptr in os/linux
• cf68d9f: 8299155: C2: SubTypeCheckNode::verify() should not produce dependencies / oop pool entries
• ... and 8 more: https://git.openjdk.org/jdk/compare/ee0f5b5ed0f8f081c5e61e2083c31863cbf14fd2...master

Your commit was automatically rebased without conflicts.

[openjdk]

@jddarcy Pushed as commit 3449324.

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

[AlanBateman]

@jddarcy Are you planning a GC of unused functions in StrictMath.c too? (for this PR I'm wondering about Java_java_lang_StrictMath_expm1).

[jddarcy]

@jddarcy Are you planning a GC of unused functions in StrictMath.c too? (for this PR I'm wondering about Java_java_lang_StrictMath_expm1).

Yes, once the port is done, I'll remove all the remaining FDLIBM C files. There are dependencies between the different C files, sinh calls expm1, etc., so to avoid needed to untangle all of those, I was going to do the removal in one step at the end.