There are two kinds of lookahead assertions: positive and negative.

有两种前进的说法：积极和消极的。

As with regular expressions, you can create either positive or negative lookahead assertions.

正如正则表达式一样，你可以创建或者正的，或者负的前观断言。

A fast carry-skip adder is proposed based on variable-sized two-level block carry-lookahead logic.

提出了一种基于方块超前进位的快速进位跳跃加法器。

A fast carry - skip adder is proposed based on variable - sized two - level block carry - lookahead logic.

提出了一种基于方块超前进位的快速进位跳跃加法器.

Negative lookahead assertion. This is the opposite of the positive assertion; it succeeds if the contained expression doesn't match at the current position in the string.

前向否定界定符。与肯定界定符相反；当所含表达式不能在字符串当前位置匹配时成功。