Revert "Fix waring: using abs() for floating point type"

This reverts commit a6a1e538928656f20e946b4f45acd4362bd0f6d0.
Because the change yields a segfault
flowgrind: properly fix compiler warning

Rewritten function to determine length of integer part of a decimal
number
Merge pull request #170 from alexander-zimmermann/next

flowgrind: properly fix compiler warning