Improves numerical precision (if applicable) using pairwise summation:
https://en.wikipedia.org/wiki/Pairwise_summation

Thanks to Rasmus Larsen for the succinct binary tree aggregation pseudocode.

Also adds AsString for Variant types: this emits the Variant as a string via
its DebugString().

PiperOrigin-RevId: 340246073
Change-Id: I009281f46cbea30d6e33ecf79a1723d62e96cc6d

The `printf` format specifier only allows `#`, `0`, `-`, `+` and space as flag characters. Others are interpreted as width/precision/length modifier or conversion specifiers. If a character does not fit into any of these sets `printf` just displays it.

Also add a test suite for `tf.strings.as_string`. Also fix the issue where the flag character was used only if width was specified.

PiperOrigin-RevId: 332553548
Change-Id: Ie57cf2a7c14d1a36097642794c14329db669bbba

This is a part of a larger migration effort for tensorflow::tstring.
See: https://github.com/tensorflow/community/pull/91
PiperOrigin-RevId: 262172788

The tf.as_string supports most of the data types (including complex64)
but not complex128.

This fix add complex128 support for tf.as_string.
Signed-off-by: NYong Tang <yong.tang.github@outlook.com>

PiperOrigin-RevId: 201110240

PiperOrigin-RevId: 201033171

PiperOrigin-RevId: 201011811

In `tf.as_string`, integers are mostly supported (`int8`, `int32`, `int64`)
but not `int16`. This fix adds the `int16` support for `tf.as_string`.
Signed-off-by: NYong Tang <yong.tang.github@outlook.com>

Change: 125063019