std.java.math

Math functions that give exactly what Java’s StrictMath gives, on every platform. That matters for code ported from Java whose results depend on the last bit, such as Minecraft’s world generation, and every nextGaussian(), which calls log. Other code should use std.math, which has the same functions under the same names, faster where a better algorithm exists.

CalxOutput

Tested

import std.java.math.{exp, log, pow}

fn main() {
    println("{log(1.0)} {log(2.0)} {log(10.0)}")
    println("{exp(1.0)} {pow(7.0, 22.0)}")
}

exp(1.0) is one ULP above E here, and pow(7.0, 22.0) one ULP below the double nearest 7²², because that’s what StrictMath gives. std.math gives 2.718281828459045 and 3.9098210485829883E18.

It has PI, E, exp, expm1, log, log10, log1p, pow, sin, cos, tan, asin, acos, atan, atan2, hypot, cbrt, sinh, cosh and tanh, with the same arguments and special values as StrictMath’s.

How it matches

• Each function is ported from fdlibm 5.3, the library StrictMath is defined by, keeping its constants and its order of operations, which decide the last bit. fdlibm’s permissive notices are kept in the source.
• Java code often calls Math, which HotSpot may replace with intrinsics that are off by an ULP. With those intrinsics off, Math and StrictMath agree, and Calx matches both (spec).
• Every function matched JDK 25’s StrictMath on 1,043,282 arguments, in debug and release builds, on Windows and Linux: zeros, subnormals, infinities, NaN, the ends of each range, numbers next to multiples of pi/2, the arguments whose reduction by pi/2 is hardest, and hundreds of thousands of random ones. tests/std/java_math.calx keeps the hardest 138.

Speed

The port keeps fdlibm’s arithmetic but not its control flow, where a change can’t alter a result: sin, tan and atan are exactly odd and cos exactly even in fdlibm, so they work on |x| and apply the sign at the end, and a case fdlibm splits off that computes what the general one does is merged into it. Nanoseconds per call on random arguments, against StrictMath on JDK 25:

Function	std.java.math	StrictMath
sin	8.1	13.6
cos	8.2	13.3
tan	10.3	12.5
exp	3.7	5.3
log	3.6	4.4
pow	29.5	56.3
atan2	9.9	18.2
acos	5.8	7.0

std.java.math is written in Calx: std/java/math.calx.