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8301205: Port fdlibm log10 to Java

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Reviewed-by: bpb
This commit is contained in:
Joe Darcy 2023-01-30 20:33:01 +00:00
parent b84f4c40fd
commit 63bb2ce8de
4 changed files with 222 additions and 15 deletions
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79
src/java.base/share/classes/java/lang/FdLibm.java
View file

@ -1,5 +1,5 @@
/*
* Copyright (c) 1998, 2021, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1998, 2023, 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
@ -745,4 +745,81 @@ class FdLibm {
}
}
}
/**
* Return the base 10 logarithm of x
*
* Method :
* Let log10_2hi = leading 40 bits of log10(2) and
* log10_2lo = log10(2) - log10_2hi,
* ivln10 = 1/log(10) rounded.
* Then
* n = ilogb(x),
* if(n<0) n = n+1;
* x = scalbn(x,-n);
* log10(x) := n*log10_2hi + (n*log10_2lo + ivln10*log(x))
*
* Note 1:
* To guarantee log10(10**n)=n, where 10**n is normal, the rounding
* mode must set to Round-to-Nearest.
* Note 2:
* [1/log(10)] rounded to 53 bits has error .198 ulps;
* log10 is monotonic at all binary break points.
*
* Special cases:
* log10(x) is NaN with signal if x < 0;
* log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
* log10(NaN) is that NaN with no signal;
* log10(10**N) = N for N=0,1,...,22.
*
* Constants:
* The hexadecimal values are the intended ones for the following constants.
* The decimal values may be used, provided that the compiler will convert
* from decimal to binary accurately enough to produce the hexadecimal values
* shown.
*/
static class Log10 {
private static double two54 = 0x1.0p54; // 1.80143985094819840000e+16;
private static double ivln10 = 0x1.bcb7b1526e50ep-2; // 4.34294481903251816668e-01
private static double log10_2hi = 0x1.34413509f6p-2; // 3.01029995663611771306e-01;
private static double log10_2lo = 0x1.9fef311f12b36p-42; // 3.69423907715893078616e-13;
private Log10() {
throw new UnsupportedOperationException();
}
public static double compute(double x) {
double y, z;
int i, k;
int hx = __HI(x); // high word of x
int lx = __LO(x); // low word of x
k=0;
if (hx < 0x0010_0000) { /* x < 2**-1022 */
if (((hx & 0x7fff_ffff) | lx) == 0) {
return -two54/0.0; /* log(+-0)=-inf */
}
if (hx < 0) {
return (x - x)/0.0; /* log(-#) = NaN */
}
k -= 54;
x *= two54; /* subnormal number, scale up x */
hx = __HI(x);
}
if (hx >= 0x7ff0_0000) {
return x + x;
}
k += (hx >> 20) - 1023;
i = (k & 0x8000_0000) >>> 31; // unsigned shift
hx = (hx & 0x000f_ffff) | ((0x3ff - i) << 20);
y = (double)(k + i);
x = __HI(x, hx); // replace high word of x with hx
z = y * log10_2lo + ivln10 * StrictMath.log(x);
return z + y * log10_2hi;
}
}
}

6
src/java.base/share/classes/java/lang/StrictMath.java
View file

@ -1,5 +1,5 @@
/*
* Copyright (c) 1999, 2022, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1999, 2023, 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
@ -281,7 +281,9 @@ public final class StrictMath {
* @return the base 10 logarithm of {@code a}.
* @since 1.5
*/
public static native double log10(double a);
public static double log10(double a) {
return FdLibm.Log10.compute(a);
}
/**
* Returns the correctly rounded positive square root of a