math: missing Nextafter32

[griesemer]

Nextafter cannot be used for float32 operands. Should probably introduce

Nextafter32
Nextafter64

and make Nextafter an "alias" for Nextafter64.

[griesemer]

Comment 1:

See also https://golang.org/cl/93550043 which implements Nextafter32 in
math/big.

[gopherbot]

Comment 2:

CL https://golang.org/cl/101750048 mentions this issue.

[griesemer]

Comment 3:

Status changed to Started.

[griesemer]

Comment 4:

This issue was closed by revision a9035ed.

Status changed to Fixed.