> 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)
> ---
>> /**
> 51,58c51,52
> <
> < #include "fdlibm.h"
> <
> < #ifdef __STDC__
> < static const double
> < #else
> < static double
> < #endif
> ---
>> static class Log {
>> private static final double
> 70c64
> < static double zero = 0.0;
> ---
>> private static double zero = 0.0;
> 72,78c66
> < #ifdef __STDC__
> < double __ieee754_log(double x)
> < #else
> < double __ieee754_log(x)
> < double x;
> < #endif
> < {
> ---
>> static double compute(double x) {
> 81c69
> < unsigned lx;
> ---
>> /*unsigned*/ int lx;
> 98c86,87
> < __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 */
> 128a118
>> }
>
>
> 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
> 53,62c53,54
> < 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
> 64c56,64
> < 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;
> 71,72c71,72
> < 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
> 75,80c75,87
> < 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;
> 82d88
> < if (hx >= 0x7ff00000) return x+x;
> 84,87c90,92
> < 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
> 90c95
> < if((0x000fffff&(2+hx))<3) { /* |f| < 2**-20 */
> ---
>> if ((0x000f_ffff & (2 + hx)) < 3) {// |f| < 2**-20
> 92,93c97,102
> < 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;
>> }
> 96,97c105,110
> < 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);
>> }
> 102c115
> < i = hx-0x6147a;
> ---
>> i = hx - 0x6_147a;
> 111c124,126
> < if(k==0) return f-(hfsq-s*(hfsq+R)); else
> ---
>> if (k == 0) {
>> return f-(hfsq-s*(hfsq+R));
>> } else {
> 112a128,131
>> }
>> } else {
>> if (k == 0) {
>> return f - s*(f - R);
> 114d132
> < if(k==0) return f-s*(f-R); else
> 115a134
>> }
>
>
> 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.
Joe Darcy has updated the pull request incrementally with two additional
commits since the last revision:
- Appease jcheck.
- Add StrictMath.log vs Math.log differences.
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/12465/files
- new: https://git.openjdk.org/jdk/pull/12465/files/b7f0e8d2..cafd1f1f
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=12465&range=02
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=12465&range=01-02
Stats: 102 lines in 2 files changed: 101 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
