[SR-6671] Decimal.leastNonzeroMagnitude, leastNormalMagnitude should have -128 exponent #4266
Description
| 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.
https://github.com/apple/swift-corelibs-foundation/blob/ee61823ae71f4c4f9ca157fd290c4b7de915b2a4/Foundation/Decimal.swift#L120
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?