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[SR-6671] Decimal.leastNonzeroMagnitude, leastNormalMagnitude should have -128 exponent #4266

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swift-ci opened this issue Dec 28, 2017 · 3 comments
Closed

[SR-6671] Decimal.leastNonzeroMagnitude, leastNormalMagnitude should have -128 exponent #4266

swift-ci opened this issue Dec 28, 2017 · 3 comments
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@xwu
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Previous ID SR-6671
Radar None
Original Reporter takasek (JIRA User)
Type Bug
Status Resolved
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Foundation
Labels Bug
Assignee @xwu
Priority Medium

md5: f8e60ccf11f2fdc6d95d64e7bcbd0e41

relates to:

  • SR-14974 Decimal.ulp produces inaccurate results

Issue Description:

`Decimal.leastNonzeroMagnitude` and `Decimal.leastNormalMagnitude` are set -127 as their exponents.

swift-corelibs-foundation/Foundation/Decimal.swift

Line 120 in ee61823

_exponent: -127,

However, you can make less value than least magnitude by such code below.

func truelyLeastDecimal() -> Decimal {
    var x = Decimal(string: "0.1")!
    var r = Decimal()
    NSDecimalPower(&r, &x, 128, .plain)
    return r
}

func p(_ d: Decimal) {
    print("=====")
    print(d)
    print(d._mantissa)
    print(d._exponent)
}
p(Decimal.leastNormalMagnitude)
p(truelyLeastDecimal())

/*
 =====
 0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001
 (1, 0, 0, 0, 0, 0, 0, 0)
 -127
 =====
 0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001
 (1, 0, 0, 0, 0, 0, 0, 0)
 -128
 */

NSDecimalNumber defines its exponent's range is down to -128.
https://developer.apple.com/documentation/foundation/nsdecimalnumber

Thus `Foundation.Decimal` should follow it. Isn't it?
@swift-ci
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Comment by Yoshitaka Seki (JIRA)

I just submitted #1386 .

@weissi
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weissi commented Apr 13, 2021

this still crashes on main:

 40> truelyLeastDecimal()
$R3: Decimal = 0.000000

 41> print(truelyLeastDecimal()) 
0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001
 42> p(truelyLeastDecimal())
Execution interrupted. Enter code to recover and continue.
Enter LLDB commands to investigate (type :help for assistance.)

@xwu
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xwu commented Aug 30, 2021

#3067

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@shahmishal shahmishal transferred this issue from apple/swift May 5, 2022
This issue was closed.
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@xwu @weissi @swift-ci