RFR: JDK-8301396: Port fdlibm expm1 to Java

Joe Darcy darcy at openjdk.org
Thu Feb 2 22:35:29 UTC 2023


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 */

-------------

Commit messages:
 - JDK-8301396: Port fdlibm expm1 to Java

Changes: https://git.openjdk.org/jdk/pull/12394/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12394&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301396
  Stats: 516 lines in 4 files changed: 497 ins; 12 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/12394.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12394/head:pull/12394

PR: https://git.openjdk.org/jdk/pull/12394


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