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WiP Redesign the encoding of Longs in JavaScript. #5205

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WiP Redesign the encoding of Longs in JavaScript. #5205

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720015d
Branchless algorithm for RuntimeLong.toDouble.
sjrd Jun 23, 2025
331baa8
Introduce code paths for Longs that are *signed* safe doubles.
sjrd Jun 23, 2025
3e51123
WiP Redesign the encoding of Longs in JavaScript.
sjrd Jun 25, 2025
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34 changes: 18 additions & 16 deletions javalib/src/main/scala/java/lang/Long.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -120,7 +120,7 @@ object Long {
if (radix == 10 || radix < Character.MIN_RADIX || radix > Character.MAX_RADIX)
toString(i)
else
toStringImpl(i, radix)
toStringImpl(i.toInt, (i >>> 32).toInt, radix)
}

@inline // because radix is almost certainly constant at call site
Expand All @@ -133,48 +133,50 @@ object Long {
val radix1 =
if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX) 10
else radix
toUnsignedStringImpl(i, radix1)
toUnsignedStringImpl(i.toInt, (i >>> 32).toInt, radix1)
}
}

// Intrinsic
@inline def toString(i: scala.Long): String = "" + i

@inline def toUnsignedString(i: scala.Long): String =
toUnsignedStringImpl(i, 10)
toUnsignedStringImpl(i.toInt, (i >>> 32).toInt, 10)

// Must be called only with valid radix
private def toStringImpl(i: scala.Long, radix: Int): String = {
val lo = i.toInt
val hi = (i >>> 32).toInt
private def toStringImpl(lo: Int, hi: Int, radix: Int): String = {
import js.JSNumberOps.enableJSNumberOps

if (lo >> 31 == hi) {
// It's a signed int32
import js.JSNumberOps.enableJSNumberOps
lo.toString(radix)
} else if (hi < 0) {
val neg = -i
"-" + toUnsignedStringInternalLarge(neg.toInt, (neg >>> 32).toInt, radix)
} else if (((hi ^ (hi >> 10)) & 0xffe00000) == 0) { // see RuntimeLong.isSignedSafeDouble
// (lo, hi) is small enough to be a Double, so toDouble is exact
makeLongFromLoHi(lo, hi).toDouble.toString(radix)
} else {
toUnsignedStringInternalLarge(lo, hi, radix)
val abs = Math.abs(makeLongFromLoHi(lo, hi))
val s = toUnsignedStringInternalLarge(abs.toInt, (abs >>> 32).toInt, radix)
if (hi < 0) "-" + s else s
}
}

// Must be called only with valid radix
private def toUnsignedStringImpl(i: scala.Long, radix: Int): String = {
val lo = i.toInt
val hi = (i >>> 32).toInt
private def toUnsignedStringImpl(lo: Int, hi: Int, radix: Int): String = {
import js.JSNumberOps.enableJSNumberOps

if (hi == 0) {
// It's an unsigned int32
import js.JSNumberOps.enableJSNumberOps
Integer.toUnsignedDouble(lo).toString(radix)
} else if ((hi & 0xffe00000) == 0) { // see RuntimeLong.isUnsignedSafeDouble
// (lo, hi) is small enough to be a Double, so toDouble is exact
makeLongFromLoHi(lo, hi).toDouble.toString(radix)
} else {
toUnsignedStringInternalLarge(lo, hi, radix)
}
}

// Must be called only with valid radix and with (lo, hi) >= 2^30
// Must be called only with valid radix and with (lo, hi) >= 2^53
@inline // inlined twice: once in toStringImpl and once in toUnsignedStringImpl
private def toUnsignedStringInternalLarge(lo: Int, hi: Int, radix: Int): String = {
import js.JSNumberOps.enableJSNumberOps
import js.JSStringOps.enableJSStringOps
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