strconv: Support for Hex Floats (like %a in C)

[gopherbot]

by odysseus9672:

What does 'go version' print?
go version go1.3beta2 +708e129e91a9 Wed May 21 16:01:54 2014 -0700 darwin/amd64

What steps reproduce the problem?
If possible, include a link to a program on play.golang.org.

1. Go does not support the hex encoded floats produceable from the C verb %a in stdio.h
and float.hex/float.fromhex in Python.
2. Example numbers:
pi = 0x1.921fb54442d18p+1
-e = -0x1.5bf0a8b145769p+1
15.39453125 = f.65 = 0x1.eca0000000000p+3
2^-1070 = 0x0.0000000000010p-1022

http://play.golang.org/p/446DOTlpbw

What happened?
A bunch of errors.

What should have happened instead?

Please provide any additional information below.

I know that Go implements an equivalent syntax in the %b verb, but having %a would be
nice for cross compatibility with C, Python, and Java. The best part is that producing
the FormatFloat part of the code is trivial. The tricky part is, as always, getting the
parser to work right.

[ianlancetaylor]

Comment 1:

Given the existence of %b, I don't see an argument for %a.  It's nice to have a syntax
similar to C and Python, but the syntax is already different, and one more difference
doesn't matter.
Leaving this open for strconv issues.

Labels changed: added repo-main, release-none.

[gopherbot]

Comment 2 by odysseus9672:

Here's the beginning of a function that produces such output. It could use some
prettying up - removal of trailing zeros, the ability to handle flags for field width,
precision, etc.

Attachments:

1. F64toHex.go (1052 bytes)

[ianlancetaylor]

Comment 3:

Thanks.  The issue tracker is not the place for patches.  Please see
http://golang.org/doc/contribute.html for how to contribute patches.

[robpike]

Comment 4:

Not worth doing.

Status changed to WorkingAsIntended.