glibc中几个数值处理函数

ceil/floor/rint/round，这几个C的数值处理函数，我们通常用它们来取整某个特定的浮点数。


— Function: double ceil (double x)

These functions round x upwards to the nearest integer, returning that value as a double. Thus, ceil (1.5) is 2.0.


— Function: double floor (double x)


These functions round x downwards to the nearest integer, returning that value as a double. Thus, floor (1.5) is 1.0 and floor (-1.5) is -2.0.


— Function: double rint (double x)

These functions round x to an integer value according to the current rounding mode.The default rounding mode is to round to the nearest integer; some machines support other modes, but round-to-nearest is always used unless you explicitly select another.


— Function: double round (double x)

These functions are similar to rint, but they round halfway cases away from zero instead of to the nearest integer (or other current rounding mode).


Examples:

1. 请注意rint(+/-0.5)和round(+/-0.5)之间的区别(对于+/-0.5，round函数总是返回远离0的值):

	0.3	0.5	0.6	-0.3	-0.5	-0.6
ceil	1	1	1	-0	-0	-0
floor	0	0	0	-1	-1	-1
rint	0	0	1	-0	-0	-1
round	0	1	1	-0	-1	-1

2. rint和round此时相同：

	1.3	1.5	1.6	-1.3	-1.5	-1.6
ceil	2	2	2	-1	-1	-1
floor	1	1	1	-2	-2	-2
rint	1	2	2	-1	-2	-2
round	1	2	2	-1	-2	-2