Expression

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This article is imported from the old MTS2 wiki. You can help Sims2Wiki by cleaning it up. It's original page with comments can be found at http://old_wiki.modthesims2.com/Expression
==Expression==

For those familiar with TS1 modding, there is nothing new here. This page is designed primarily for the newcomer who does not have any previous experience with SimAntics.

This is by far the most used BHAV operation and, therefore, one of the first an aspiring behavioral modder should learn. At its heart, Expression is a fairly simple instruction, taking two items and performing a logical comparison or mathematical calculation with them.

The structure (with the exception of the as yet unknown bytes) is also fairly simple. We will use the following example instruction to explore the structure further:

OpCode, Tru, Fal, Flag, op1, op2, op3, op4, op5, op6, op7, op8, un1, un2, un3, un4, un5, un6, un7, un8


0x0002, 2, Err, 00, 00, 00, 00, 00, 00, 05, 19, 09, 00, 00, 00, 00, 00, 00, 00, 00

The True and False lines are the same as in any other instruction, so we can ignore them for now. The Flag is still not fully understood, so we will not be discussing it either. The 8 Unknown bytes (un1 - un8) will also not be discussed as they do not appear to be used directly by the 0x0002 instruction.

This only leaves us with the 8 ops (op1 - op8), which break down as follows:

op6 is the Operator, which tells the game which mathematical/logical operation to perform op7 is the first (or left-side) Operand op8 is the second (or right-side) Operand op1 and op2 are read together as a single little-endian short. It is an argument for the first Operand op3 and op4 are read together as a single little-endian short. It is an argument for the second Operand op5 was never completely understood in TS1. Either it is some type of flag or is unused.

So in our example instruction: the Operator is 05 (Assign To:) the first Operand is 19 (Local Variable) which has an argument of 00 (numeric 0) the second Operand is 09 (Parameters) which has an argument of 00 (numeric 0)

Our instruction would therefore be read as "Local Variable 0 Assign To: Parameters 0". In simple terms, this means "the value for Local Variable 0 = the value listed in Parameter 0"

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