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[SPCA] Fix various errors

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Janis Hutz
2026-01-23 10:33:49 +01:00
parent b86fd00a60
commit 25b3381294
15 changed files with 36 additions and 23 deletions
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5
semester3/spca/parts/00_asm/03_operations/02_condition-codes.tex
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@@ -11,12 +11,13 @@ The following condition codes were covered in the lecture (operation: \texttt{t
\content{Explicit computation}
In the below explanations, we always assume \texttt{src2 = b} and \texttt{src1 = a}
To explicitly compute them, we can use the \texttt{cmpX src2, src1} instruction (with X again any of the size postfixes),
To explicitly compute them, we can use the \texttt{cmpX src2, src1} (i.e. for easier understanding, \texttt{cmpX b, a}) instruction (with X again any of the size postfixes),
that essentially computes $(a - b)$ without setting a destination register.
When we execute that instruction, \texttt{CF} is set if \texttt{a < b} (unsigned), \texttt{ZF} is set if \texttt{a == b}, \texttt{SF} is set if \texttt{a < b} (signed)
and \texttt{OF} is set as above, where \texttt{t = a - b}.
Another instruction that is used is \texttt{testX src2, src1} (X again a size postfix), and acts like computing \texttt{a \& b} and where \texttt{ZF} is set if \texttt{a \& b == 0}
Another instruction that is used is \texttt{testX src2, src1} (X again a size postfix, easier: \texttt{testX b, a}), and acts like computing \texttt{a \& b} and where \texttt{ZF} is set if \texttt{a \& b == 0}
and \texttt{SF} is set if \texttt{a \& b < 0}.
\content{Zeroing register} We can use a move instruction, but that is less efficient than using \texttt{xorl reg, reg}, where \texttt{reg} is the 32-bit version of the reg we want to zero.

10
semester3/spca/parts/00_asm/03_operations/03_jumping.tex
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@@ -1,8 +1,8 @@
\subsubsection{Jumping}
To jump, use \texttt{jmp <label>} (unconditional jump) or the \texttt{jC} instructions, with \texttt{C} from table \ref{tab:condition-codes}
To jump, use \texttt{jmp <label>} (unconditional jump) or the \texttt{jC <label>} instructions, with \texttt{C} from table \ref{tab:condition-codes}
\begin{table}[h!]
\begin{tables}{lll}{\texttt{setX} & Condition & Description}
\begin{tables}{lll}{\texttt{setC} & Condition & Description}
\texttt{e} & \verb|ZF| & Equal / Zero \\
\texttt{ne} & \verb+~ZF+ & Not Equal / Not Zero \\
\texttt{s} & \verb|SF| & Negative \\
@@ -23,11 +23,11 @@ To jump, use \texttt{jmp <label>} (unconditional jump) or the \texttt{jC} instru
Similar to \texttt{jC}, the same postfixes can be applied to \texttt{cmovC}, for example:
\begin{minted}{gas}
cmpl %eax, %edx
cmovle %edx, %eax
cmpl %eax, %edx # computes (edx - eax) without overwriting edx
cmovle %edx, %eax # only copies edx into eax if edx <= eax
\end{minted}
Will move \verb|%edx| into \verb|%eax|, only if \verb|%edx| is less or equal (\verb|le|) \verb|%eax|.
Due to the computed condition flags, this will move \verb|%edx| into \verb|%eax|, only if \verb|%edx| is less than or equal (\verb|le|) to \verb|%eax|.
This can be used to, for example, compile ternary expressions from \verb|C| to Assembly.
However, this requires evaluating both possible expressions, which may lead to a (significant) performance overhead.