boost::unit_test::data::random(-FLT_MAX, FLT_MAX) only generates +Infinity - c++

Question

I'm using boost::unit_test::data::random (with boost-1.61.0_1 installed) and I'm having some issues generating random floats using boost::unit_test::data::random(-FLT_MAX,FLT_MAX). It only seems to generate +Infinity.
Through trial and error, I found that I could generate random floats in [-FLT_MAX,-FLT_MAX * 2^-25) and [-FLT_MAX * 2^-25, FLT_MAX) separately, which gives me a possible work-around, but I'm still curious as to what I'm doing wrong trying to generate floats in [-FLT_MAX, FLT_MAX).
#define BOOST_TEST_MODULE example
#include <boost/test/included/unit_test.hpp>
#include <boost/test/data/monomorphic.hpp>
#include <boost/test/data/test_case.hpp>
#include <cfloat>
inline void in_range(float const & min, float const & x, float const & max) {
BOOST_TEST_REQUIRE(min <= x);
BOOST_TEST_REQUIRE(x < max);
}
static constexpr float lo{-FLT_MAX / (1024.0 * 1024.0 * 32.0)};
// this test passes
namespace bdata = boost::unit_test::data;
BOOST_DATA_TEST_CASE(low_floats, bdata::random(-FLT_MAX, lo) ^ bdata::xrange(100), x,
index) {
#pragma unused(index)
in_range(-FLT_MAX, x, lo);
}
// this test passes
BOOST_DATA_TEST_CASE(high_floats, bdata::random(lo, FLT_MAX) ^ bdata::xrange(100), x,
index) {
#pragma unused(index)
in_range(lo, x, FLT_MAX);
}
// this test fails
BOOST_DATA_TEST_CASE(all_floats, bdata::random(-FLT_MAX, FLT_MAX) ^ bdata::xrange(100), x,
index) {
#pragma unused(index)
in_range(-FLT_MAX, x, FLT_MAX);
}
results in:
$ ./example
Running 300 test cases...
example.cpp:9: fatal error: in "all_floats": critical check x < max has failed [inf >= 3.40282347e+38]
Failure occurred in a following context:
x = inf; index = 0;
...
example.cpp:9: fatal error: in "all_floats": critical check x < max has failed [inf >= 3.40282347e+38]
Failure occurred in a following context:
x = inf; index = 99;
*** 100 failures are detected in the test module "example"

Answer 1

boost::unit_test::data::random uses std::uniform_real_distribution, which has the requirement:
Requires: a ≤ b and b - a ≤ numeric_limits<RealType>::max().
In your case, b - a is 2 * FLT_MAX, which is +Inf in float.
You could use your workaround, or you could generate in double and cast back to float.