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8362376: Use @Stable annotation in Java FDLIBM implementation #26341

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7fec151
JDK-8362376: Use @Stable annotation in Java FDLIBM implementation
jddarcy Jul 16, 2025
a7b86ee
Respond to review feedback and update copyright.
jddarcy Jul 17, 2025
5e1233b
Implement review feedback.
jddarcy Jul 17, 2025
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46 changes: 32 additions & 14 deletions src/java.base/share/classes/java/lang/FdLibm.java
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/*
* Copyright (c) 1998, 2024, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1998, 2025, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
Expand All @@ -25,6 +25,8 @@

package java.lang;

import jdk.internal.vm.annotation.Stable;

/**
* Port of the "Freely Distributable Math Library", version 5.3, from
* C to Java.
Expand Down Expand Up @@ -451,7 +453,9 @@ static double compute(double x) {
*/
private static final double
pio4 = 0x1.921fb54442d18p-1, // 7.85398163397448278999e-01
pio4lo= 0x1.1a62633145c07p-55, // 3.06161699786838301793e-17
pio4lo= 0x1.1a62633145c07p-55; // 3.06161699786838301793e-17
@Stable
private static final double
T[] = {
Comment on lines +457 to 459
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The legacy C‑like array field syntax is confusing in Java, and it’s not used for the @Stable int[] arrays below.

Suggested change
@Stable
private static final double
T[] = {
@Stable
private static final double[] T = {

Or at least put the T[] on the same line so that it’s clear why this field has @Stable, since regular static final doubles are already constant folded and @wenshao’s comment1 confused me on the “Conversation” tab, since it was missing the T[] there.

Suggested change
@Stable
private static final double
T[] = {
@Stable
private static final double T[] = {

Footnotes

  1. https://github.com/openjdk/jdk/pull/26341#discussion_r2213012163 ↩

0x1.5555555555563p-2, // 3.33333333333334091986e-01
0x1.111111110fe7ap-3, // 1.33333333333201242699e-01
Expand Down Expand Up @@ -546,6 +550,7 @@ static final class RemPio2 {
/*
* Table of constants for 2/pi, 396 Hex digits (476 decimal) of 2/pi
*/
@Stable
private static final int[] two_over_pi = {
0xA2F983, 0x6E4E44, 0x1529FC, 0x2757D1, 0xF534DD, 0xC0DB62,
0x95993C, 0x439041, 0xFE5163, 0xABDEBB, 0xC561B7, 0x246E3A,
Expand All @@ -560,6 +565,7 @@ static final class RemPio2 {
0x4D7327, 0x310606, 0x1556CA, 0x73A8C9, 0x60E27B, 0xC08C6B,
};

@Stable
private static final int[] npio2_hw = {
0x3FF921FB, 0x400921FB, 0x4012D97C, 0x401921FB, 0x401F6A7A, 0x4022D97C,
0x4025FDBB, 0x402921FB, 0x402C463A, 0x402F6A7A, 0x4031475C, 0x4032D97C,
Expand Down Expand Up @@ -807,8 +813,10 @@ static final class KernelRemPio2 {
* to produce the hexadecimal values shown.
*/

@Stable
private static final int init_jk[] = {2, 3, 4, 6}; // initial value for jk
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Suggested change
private static final int init_jk[] = {2, 3, 4, 6}; // initial value for jk
@Stable private static final int init_jk[] = {2, 3, 4, 6}; // initial value for jk

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Suggested change
private static final int init_jk[] = {2, 3, 4, 6}; // initial value for jk
@Stable
private static final int[] init_jk = {2, 3, 4, 6}; // initial value for jk

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Missed that array on my edit; will add. Thanks.


@Stable
private static final double PIo2[] = {
0x1.921fb4p0, // 1.57079625129699707031e+00
0x1.4442dp-24, // 7.54978941586159635335e-08
Expand Down Expand Up @@ -1232,20 +1240,23 @@ static double compute(double x) {
static final class Atan {
private Atan() {throw new UnsupportedOperationException();}

@Stable
private static final double atanhi[] = {
0x1.dac670561bb4fp-2, // atan(0.5)hi 4.63647609000806093515e-01
0x1.921fb54442d18p-1, // atan(1.0)hi 7.85398163397448278999e-01
0x1.f730bd281f69bp-1, // atan(1.5)hi 9.82793723247329054082e-01
0x1.921fb54442d18p0, // atan(inf)hi 1.57079632679489655800e+00
};

@Stable
private static final double atanlo[] = {
0x1.a2b7f222f65e2p-56, // atan(0.5)lo 2.26987774529616870924e-17
0x1.1a62633145c07p-55, // atan(1.0)lo 3.06161699786838301793e-17
0x1.007887af0cbbdp-56, // atan(1.5)lo 1.39033110312309984516e-17
0x1.1a62633145c07p-54, // atan(inf)lo 6.12323399573676603587e-17
};

@Stable
private static final double aT[] = {
0x1.555555555550dp-2, // 3.33333333333329318027e-01
-0x1.999999998ebc4p-3, // -1.99999999998764832476e-01
Expand Down Expand Up @@ -2245,12 +2256,14 @@ else if (j < 0xBB67A)

// Compute ss = s_h + s_l = (x-1)/(x+1) or (x-1.5)/(x+1.5)

final double BP[] = {1.0,
1.5};
final double DP_H[] = {0.0,
0x1.2b80_34p-1}; // 5.84962487220764160156e-01
final double DP_L[] = {0.0,
0x1.cfde_b43c_fd006p-27};// 1.35003920212974897128e-08
// final double BP[] = {1.0,
// 1.5};
// final double DP_H[] = {0.0,
// 0x1.2b80_34p-1}; // 5.84962487220764160156e-01
final double DP_H1 = 0x1.2b80_34p-1;
// final double DP_L[] = {0.0,
// 0x1.cfde_b43c_fd006p-27};// 1.35003920212974897128e-08
final double DP_L1 = 0x1.cfde_b43c_fd006p-27;

// Poly coefs for (3/2)*(log(x)-2s-2/3*s**3
final double L1 = 0x1.3333_3333_33303p-1; // 5.99999999999994648725e-01
Expand All @@ -2259,15 +2272,17 @@ else if (j < 0xBB67A)
final double L4 = 0x1.1746_0a91_d4101p-2; // 2.72728123808534006489e-01
final double L5 = 0x1.d864_a93c_9db65p-3; // 2.30660745775561754067e-01
final double L6 = 0x1.a7e2_84a4_54eefp-3; // 2.06975017800338417784e-01
u = x_abs - BP[k]; // BP[0]=1.0, BP[1]=1.5
v = 1.0 / (x_abs + BP[k]);

double BP_k = 1.0 + 0.5*k; // BP[0]=1.0, BP[1]=1.5
u = x_abs - BP_k;
v = 1.0 / (x_abs + BP_k);
ss = u * v;
s_h = ss;
s_h = __LO(s_h, 0);
// t_h=x_abs + BP[k] High
t_h = 0.0;
t_h = __HI(t_h, ((ix >> 1) | 0x20000000) + 0x00080000 + (k << 18) );
t_l = x_abs - (t_h - BP[k]);
t_l = x_abs - (t_h - BP_k);
s_l = v * ((u - s_h * t_h) - s_h * t_l);
// Compute log(x_abs)
s2 = ss * ss;
Expand All @@ -2285,12 +2300,12 @@ else if (j < 0xBB67A)
p_h = __LO(p_h, 0);
p_l = v - (p_h - u);
z_h = CP_H * p_h; // CP_H + CP_L = 2/(3*log2)
z_l = CP_L * p_h + p_l * CP + DP_L[k];
z_l = CP_L * p_h + p_l * CP + DP_L1*k;
// log2(x_abs) = (ss + ..)*2/(3*log2) = n + DP_H + z_h + z_l
t = (double)n;
t1 = (((z_h + z_l) + DP_H[k]) + t);
t1 = (((z_h + z_l) + DP_H1*k) + t);
t1 = __LO(t1, 0);
t2 = z_l - (((t1 - t) - DP_H[k]) - z_h);
t2 = z_l - (((t1 - t) - DP_H1*k) - z_h);
}

// Split up y into (y1 + y2) and compute (y1 + y2) * (t1 + t2)
Expand Down Expand Up @@ -2430,13 +2445,16 @@ else if (j < 0xBB67A)
static final class Exp {
private Exp() {throw new UnsupportedOperationException();}

@Stable
private static final double[] half = {0.5, -0.5,};
private static final double huge = 1.0e+300;
private static final double twom1000= 0x1.0p-1000; // 9.33263618503218878990e-302 = 2^-1000
private static final double o_threshold= 0x1.62e42fefa39efp9; // 7.09782712893383973096e+02
private static final double u_threshold= -0x1.74910d52d3051p9; // -7.45133219101941108420e+02;
@Stable
private static final double[] ln2HI ={ 0x1.62e42feep-1, // 6.93147180369123816490e-01
-0x1.62e42feep-1}; // -6.93147180369123816490e-01
@Stable
private static final double[] ln2LO ={ 0x1.a39ef35793c76p-33, // 1.90821492927058770002e-10
-0x1.a39ef35793c76p-33}; // -1.90821492927058770002e-10
private static final double invln2 = 0x1.71547652b82fep0; // 1.44269504088896338700e+00
Expand Down