pi constant

[vicuna]

Original bug ID: 4170
Reporter: Richard Jones
Assigned to: @garrigue
Status: resolved (set by @alainfrisch on 2016-12-07T17:42:27Z)
Resolution: suspended
Priority: normal
Severity: feature
Version: 3.09.2
Category: standard library
Related to: #5173
Monitored by: mehdi warwick @Chris00

Bug description

The stdlib should (IMHO) define a pi constant in Pervasives.

[vicuna]

Comment author: @garrigue

My standard code for pi is acos(-1.)
Is this too long?

[vicuna]

Comment author: Richard Jones

Since you ask ...

Is acos(-1.) the most accurate pi considering either the IEEE representation or the longer internal representation used by x86?

I know that glibc defines this constant carefully so that the most accurate pi is used. (glibc also provides long-double -- 128 bit -- variants but I guess we can't use those in OCaml).

[vicuna]

Comment author: warwick

I suggested a similar thing in issue 005173. I think having a predefined value "pi" is a lot clearer than having to write acos(-1.) ... or acos(-.1.)

[vicuna]

Comment author: @alainfrisch

Sounds like a useful addition. A PR would be appreciated!