Compilation Principle Quaternary Problem, Seeking Explanation,

Okay, I'll help you understand, let's look at the basics first:

Quaternions are a more commonly used intermediate form. The four components of a quaternion are: the operator op, the first and second operators arg1 and arg@ and the result result.

Operators and results sometimes refer to user-defined variables, and sometimes refer to temporary variables introduced by the compiler. For example, the quaternion of a = b*c + b*d is expressed as follows:

1）（*b， c， t1）

2）（*b， d， t2）

3）（+t1， t2， t3）

4）（∶=，t3， －a）

The main difference between a quaternion and a ternary is that a quaternion's reference to an intermediate result must be through a given name, whereas a ternary is numbered by a ternary that produces an intermediate result. That is, the connection between the quaternions is achieved through temporary variables.

Sometimes, to be more intuitive, the form of the quaternion is also written as a simple assignment form or a more understandable form. For example, write the above quaternion sequence as:

1）t1∶=b*c

2）t2∶=b*d

3）t3∶=t1+t2

4）a∶=t3

Write (jump, ,l) as goto l

Write (jrop,b,c,l) as if b rop c goto l

Okay, let's analyze a This is an expression, and its result is either 0 or 1, because there is no specification of where this expression is stored, so a temporary variable is needed to store it, in your case, t. Obviously, t has two values: 0 or 1

Therefore, there is. 101 t:=0 (this is the exit with a false expression).

103 t:=1 (this is the exit for the expression to be true).

Because your expression has only one a100: if a101: t:=0 (otherwise, enter a fake exit).

102: goto 104 (of course, you have to skip the true outlet, otherwise the value of t will enter the real outlet again, and become true).

103: t:=1

104: (The program continues).

Is the landlord not written in the original style? Look at your formula, the original formula should be.

if aelse t=0

The quaternion is one of the more commonly used intermediate forms.

Form. **Quaternion expressions for segments.

101 t:=0 (exit with false expression).

103 t:=1 (the expression is true).

Because the user's expression has only one a100: if a101: t:=0 (otherwise, enter a fake exit).

102: goto 104 (to skip the true exit, otherwise the value of t will enter the true exit again, true).

103: t:=1

104: (The program continues).