Next up on the FDLIBM porting countdown, the log method.
Original C vs transliteration port:
$ diff -w Log.c Log.translit.java
1c1
< /* __ieee754_log(x)
---
> /**
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<
< #include "fdlibm.h"
<
< #ifdef __STDC__
< static const double
< #else
< static double
< #endif
---
> static class Log {
> private static final double
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< static double zero = 0.0;
---
> private static double zero = 0.0;
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< #ifdef __STDC__
< double __ieee754_log(double x)
< #else
< double __ieee754_log(x)
< double x;
< #endif
< {
---
> static double compute(double x) {
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< unsigned lx;
---
> /*unsigned*/ int lx;
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< __HI(x) = hx|(i^0x3ff00000); /* normalize x or x/2 */
---
> // __HI(x) = hx|(i^0x3ff00000); /* normalize x or x/2 */
> x =__HI(x, hx|(i^0x3ff00000)); /* normalize x or x/2 */
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> }
Transliteration port vs more idiomatic port:
$ diff -w Log.translit.java Log.fdlibm.java
2c2
< * Return the logarithm of x
---
> * Return the (natural) logarithm of x
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< ln2_hi = 6.93147180369123816490e-01, /* 3fe62e42 fee00000 */
< ln2_lo = 1.90821492927058770002e-10, /* 3dea39ef 35793c76 */
< two54 = 1.80143985094819840000e+16, /* 43500000 00000000 */
< Lg1 = 6.666666666666735130e-01, /* 3FE55555 55555593 */
< Lg2 = 3.999999999940941908e-01, /* 3FD99999 9997FA04 */
< Lg3 = 2.857142874366239149e-01, /* 3FD24924 94229359 */
< Lg4 = 2.222219843214978396e-01, /* 3FCC71C5 1D8E78AF */
< Lg5 = 1.818357216161805012e-01, /* 3FC74664 96CB03DE */
< Lg6 = 1.531383769920937332e-01, /* 3FC39A09 D078C69F */
< Lg7 = 1.479819860511658591e-01; /* 3FC2F112 DF3E5244 */
---
> ln2_hi = 0x1.62e42feep-1, // 6.93147180369123816490e-01
> ln2_lo = 0x1.a39ef35793c76p-33, // 1.90821492927058770002e-10
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< private static double zero = 0.0;
---
> Lg1 = 0x1.5555555555593p-1, // 6.666666666666735130e-01
> Lg2 = 0x1.999999997fa04p-2, // 3.999999999940941908e-01
> Lg3 = 0x1.2492494229359p-2, // 2.857142874366239149e-01
> Lg4 = 0x1.c71c51d8e78afp-3, // 2.222219843214978396e-01
> Lg5 = 0x1.7466496cb03dep-3, // 1.818357216161805012e-01
> Lg6 = 0x1.39a09d078c69fp-3, // 1.531383769920937332e-01
> Lg7 = 0x1.2f112df3e5244p-3; // 1.479819860511658591e-01
>
> private static final double zero = 0.0;
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< hx = __HI(x); /* high word of x */
< lx = __LO(x); /* low word of x */
---
> hx = __HI(x); // high word of x
> lx = __LO(x); // low word of x
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< if (hx < 0x00100000) { /* x < 2**-1022 */
< if (((hx&0x7fffffff)|lx)==0)
< return -two54/zero; /* log(+-0)=-inf */
< if (hx<0) return (x-x)/zero; /* log(-#) = NaN */
< k -= 54; x *= two54; /* subnormal number, scale up x */
< hx = __HI(x); /* high word of x */
---
> if (hx < 0x0010_0000) { // x < 2**-1022
> if (((hx & 0x7fff_ffff) | lx) ==0) { // log(+-0) = -inf
> return -TWO54/zero;
> }
> if (hx < 0) { // log(-#) = NaN
> return (x - x)/zero;
> }
> k -= 54;
> x *= TWO54; // subnormal number, scale up x
> hx = __HI(x); // high word of x
> }
> if (hx >= 0x7ff0_0000) {
> return x+x;
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< if (hx >= 0x7ff00000) return x+x;
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< hx &= 0x000fffff;
< i = (hx+0x95f64)&0x100000;
< // __HI(x) = hx|(i^0x3ff00000); /* normalize x or x/2 */
< x =__HI(x, hx|(i^0x3ff00000)); /* normalize x or x/2 */
---
> hx &= 0x000f_ffff;
> i = (hx + 0x9_5f64) & 0x10_0000;
> x =__HI(x, hx|(i ^ 0x3ff0_0000)); // normalize x or x/2
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< if((0x000fffff&(2+hx))<3) { /* |f| < 2**-20 */
---
> if ((0x000f_ffff & (2 + hx)) < 3) {// |f| < 2**-20
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< if (k==0) return zero;
< else {dk=(double)k; return dk*ln2_hi+dk*ln2_lo;}
---
> if (k == 0) {
> return zero;
> } else {
> dk = (double)k;
> return dk*ln2_hi + dk*ln2_lo;
> }
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< if(k==0) return f-R; else {dk=(double)k;
< return dk*ln2_hi-((R-dk*ln2_lo)-f);}
---
> if (k == 0) {
> return f - R;
> } else {
> dk = (double)k;
> return dk*ln2_hi - ((R - dk*ln2_lo) - f);
> }
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< i = hx-0x6147a;
---
> i = hx - 0x6_147a;
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< if(k==0) return f-(hfsq-s*(hfsq+R)); else
---
> if (k == 0) {
> return f-(hfsq-s*(hfsq+R));
> } else {
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> }
> } else {
> if (k == 0) {
> return f - s*(f - R);
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< if(k==0) return f-s*(f-R); else
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> }
The transliteration port passes the "exhausting" test of all float arguments
when run against a JDK 20 build. The idiomatic port matches the transliteration
port on the same test.
-------------
Commit messages:
- Appease jcheck.
- Preliminary version of regression test.
- Switch to hex literals.
- JDK-8301202: Port fdlibm log to Java
Changes: https://git.openjdk.org/jdk/pull/12465/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12465&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8301202
Stats: 392 lines in 3 files changed: 391 ins; 0 del; 1 mod
Patch: https://git.openjdk.org/jdk/pull/12465.diff
Fetch: git fetch https://git.openjdk.org/jdk pull/12465/head:pull/12465
PR: https://git.openjdk.org/jdk/pull/12465
