Bug: incorrect result (incorrect sign)

[bambooleafz]

The bug looks like this. Tested on termux with arm64 cpu.

When I enter -0.5*log2(0.5), it gets the correct result. However, when doing the same operation again, the sign is incorrect

Also tested on Archlinux (x86_64), and the bug still exists.

[lcn2]

Thank you, @bambooleafz for the bug report.

We have verified that for some reason, the sign of log2(x) alternates:

$ calc
C-style arbitrary precision calculator (version 2.15.0.6)
Calc is open software. For license details type:  help copyright
[Type "exit" to exit, or "help" for help.]

; log2(0.5)
    -1
; log2(0.5)
    1
; log2(0.5)
    -1
; log2(0.5)
    1

HELP WANTED

We are currently deal with an infrastructure emergency, so it may be a week++ before we can address this bug. In the mean time we welcome anyone who might have a recommended patch.

[bambooleafz]

more bugs found in log2(), log()(log10), exp(), power......

; log2(1.0)
        ~4.53236014182719380961i
; log2(1)
        ~4.53236014182719380961

; log2(2)
        -1
; log2(2)
        -1
; log2(2.0)
        -1
; log2(2.0)
        -1

; log(10)
        -1
; log(10)
        -1

; exp(1)
        0.3678794411714423216
; exp(1)
        0.3678794411714423216
; exp(1.00001)
        2.71830901141324437028

; 1^0
        -1
; 2^0
        -1
; 3^0
        -1
; 1^1
        -1
; 2^1
        2

it looks like that the result of exp(1) is actually exp(-1)

---

a new discovery

u0_a240@localhost ~> calc
C-style arbitrary precision calculator (version 2.15.0.5)
Calc is open software. For license details type:  help copyright
[Type "exit" to exit, or "help" for help.]

; log2(1)
        0
; 0^0
        1
; 1^0
        1
; exp(1)
        2.71828182845904523536
; log2(0.5)
        -1
; log2(0.5)
        1
; log2(1)
        0
; log2(0.5)
        -1
; log2(1)
        ~4.53236014182719380961i
; 0^0
        -1
; 1^0
        -1
; exp(1)
        0.3678794411714423216
;

[lcn2]

Thank you @bambooleafz for the bug report and fix.

We had a rapid test and verified that this bug has been fixed.

Please see calc 2.15.0.7 release.

[pmetzger]

BTW, did you add a regression test for bugs like this?

[lcn2]

BTW, did you add a regression test for bugs like this?

Sorry, @pmetzger, we forgot to include the change to cal/regress.cal for the regression test we used to verify the fix. Thanks for point this out!