1.-1.e-13=1-1e-13
1.-3.1=1-3.1

If the result of the expression is within 10--12 of an integer, the function produces a character value representing that integer.
以上是SAS Help原话，即integer取整的精度在1e-12，在整数N加减1e-12范围内的，都被视作N
之后的SAS Help就是
If the result of the expression is positive, INTEGER returns the same result as FLOOR. If the result of the expression is negative, INTEGER returns the same result as CEIL. An expression with a missing value produces a missing value.
描述相关作取整的算法以及缺失值处理
希望对你有帮助，呵呵