SI-10148 Follow Java for float literals

[som-snytt]

Use Float.parseFloat instead of converting from Double.
Error when a value rounds to zero.

JIRA: https://issues.scala-lang.org/browse/SI-10148

[janekdb]

Why no check using Float.MinValue? Probably demonstrating my ignorance of something here!

[som-snytt]

My name isn't ScalaCheck. Also, the difference is just a sign bit which is turned on by a leading midlevel horizontal bar symbol. Of course, the test wouldn't hurt.

[janekdb]

Ignorance of IEEE 754 fully demoed (by me)! Java MIN_VALUE is not the negative float with the greatest magnitude but the smallest positive nonzero value.

https://docs.oracle.com/javase/7/docs/api/java/lang/Float.html#MIN_VALUE

Having said that why not add a check for the effect of a leading hyphen-minus?

[som-snytt]

OK, if I have time to switch my repo back to this branch on my old home machine.

There's a puzzler (BTW) that turns on the fact that -1.0f is a literal. See here.

[SethTisue]

thx AP!

[SethTisue]

this turned up in the community build:

[breeze] [error] /Users/tisue/community.212/target-0.9.7-RC1/project-builds/breeze-ef73d8d5e54fa4ff81b6f6abfe9e238739cc5d8a/math/src/test/scala/breeze/signal/filter/DesignFilterTest.scala:53: double precision floating point number too small
[breeze] [error]   val testFirwin4 = DenseVector( -0.000000000000000000e+00, 3.794040820411270776e-01, 3.794040820411272441e-01, -0.000000000000000000e+00)
[breeze] [error]                                   ^
[breeze] [error] /Users/tisue/community.212/target-0.9.7-RC1/project-builds/breeze-ef73d8d5e54fa4ff81b6f6abfe9e238739cc5d8a/math/src/test/scala/breeze/signal/filter/DesignFilterTest.scala:53: double precision floating point number too small
[breeze] [error]   val testFirwin4 = DenseVector( -0.000000000000000000e+00, 3.794040820411270776e-01, 3.794040820411272441e-01, -0.000000000000000000e+00)
[breeze] [error]                                                                                                                  ^
[breeze] [error] two errors found

is this a regression, or is the code in breeze erroneous...?

[som-snytt]

Zero is pretty small. It looks like the little heuristic for testing whether you said zero is not right.