It is undefined behaviour in C99 if the floating point number is less than or equal to -1.0. If it's in the range (-1.0, 0.0), the resulting value will be 0.
From C99, §6.3.1.4, paragraph 1
When a finite value of real floating type is converted to an integer type other than _Bool, the fractional part is discarded (i.e., the value is truncated toward zero). If the value of the integral part cannot be represented by the integer type, the behavior is undefined
Footnote 50 clarifies the behaviour for the (-1.0, 0.0) range.
