sqrt calculates incorrectly with elastic_fixed_point

[hbe72]

Simple test to copy paste to test/fixed_point/extras.cpp

using cnl::fixed_point;
using cnl::elastic_fixed_point;
//cnl::sqrt
TEST(utils_tests, sqrt)
{
    EXPECT_FLOAT_EQ(static_cast<float>(sqrt(fixed_point<cnl::int32, -20>(0))), 0.0f);
    EXPECT_FLOAT_EQ(static_cast<float>(sqrt(fixed_point<cnl::int32, -20>(2.0))), 1.414213562373095f);
    EXPECT_FLOAT_EQ(static_cast<float>(sqrt(fixed_point<cnl::int32, -20>(4.0))), 2.0f);
    EXPECT_FLOAT_EQ(static_cast<float>(sqrt(elastic_fixed_point<32, -20>(0))), 0.0f);
    EXPECT_FLOAT_EQ(static_cast<float>(sqrt(elastic_fixed_point<32, -20>(2.0))), 1.414213562373095f);
    EXPECT_FLOAT_EQ(static_cast<float>(sqrt(elastic_fixed_point<32, -20>(4.0))), 2.0f);
}

Fails with

<path>/cnl/cmake-build-debug/src/test/fp_test --gtest_filter=* --gtest_color=no
<path>/cnl/src/test/fixed_point/extras.cpp:55: Failure
Expected equality of these values:
  static_cast<float>(sqrt(elastic_fixed_point<32, -20>(2.0)))
    Which is: 2
  1.414213562373095f
    Which is: 1.4142135

<path>/cnl/src/test/fixed_point/extras.cpp:56: Failure
Expected equality of these values:
  static_cast<float>(sqrt(elastic_fixed_point<32, -20>(4.0)))
    Which is: 2.8284264
  2.0f
    Which is: 2

[johnmcfarlane]

Thanks!