[SPCA] more assembly

semester3/spca/code-examples/01_asm/02_max.s

@@ -0,0 +1,9 @@
+max:
+    cmpl %esi, %edi     // Set condition flags
+    jle .IF             // Conditional jump if %edi <= %esi
+    movl %edi, %edx     // %edi -> return register
+    jmp .ELSE
+.IF:
+    movl %esi, %edx     // &esi -> return register
+.ELSE:
+    ret

semester3/spca/code-examples/01_asm/03_absdiff.s

@@ -0,0 +1,8 @@
+absdiff:
+    movl %edi, %eax     
+    subl %esi, %eax     // arg2 - arg1 -> eax
+    movl %esi, %edx     
+    subl %edi, %edx     // arg1 - arg2 -> edx
+    cmpl %esi, %edi     // Set condition flags
+    cmovle %edx, %eax   // edx -> eax, only if eax <= edx
+    ret

semester3/spca/parts/00_asm/03_operations.tex

@@ -1,10 +1,12 @@
 \subsection{Operations}
 Assembly operations include performing arithmetic or logic functions on registers or memory data,
-transferring data between memory and registers and transferring control (conditional or unconditional jumps)
+transferring data between memory and registers and transferring control (conditional or unconditional jumps).\\
+Note that \verb|move| instructions \textit{cannot} move data directly from memory to memory.
 
 Most of the memory-related instructions in \texttt{x86} assembly have the format
 \mint{asm}|movq dest, src|
-whereas arithmetic / logic operations have the format inversed (below \texttt{X} is to be replced with size postfix).
+
+Arithmetic / logic operations have the format inversed (below \texttt{X} is to be replced with size postfix).
 \begin{tables}{lll}{Mnemonic & Format             & Computation}
               \texttt{addl}  & \texttt{Src, Dest} & \texttt{Dest} $\gets$ \texttt{Dest + Src}               \\
               \texttt{subX}  & \texttt{Src, Dest} & \texttt{Dest} $\gets$ \texttt{Dest - Src}               \\

semester3/spca/parts/00_asm/04_control-flow.tex

@@ -0,0 +1,15 @@
+\newpage
+\subsection{Control Flow}
+
+Control flow structures from \verb|C| like \verb|if/else| or \verb|for| are compiled into assembly mainly using jumps and conditional \verb|move|.
+
+By the nature of Assembly and thanks to compilers optimizing aggressively, there is no \textit{single} definitive translation of the \verb|C| control structures: The compiler may translate it very differently depending on the context of the program.
+
+\subsubsection{Conditional statements}
+A function using an \verb|if/else| construct to choose the maximum of $2$ numbers might compile like this:
+
+\inputcodewithfilename{gas}{code-examples/01_asm/}{02_max.s}
+
+A function computing the absolute difference $|x-y|$ using an \verb|if/else| construct, might use a conditional \verb|move| instead:
+
+\inputcodewithfilename{gas}{code-examples/01_asm/}{03_absdiff.s}

semester3/spca/spca-summary.tex

@@ -86,6 +86,7 @@ If there are changes and you'd like to update this summary, please open a pull r
 \input{parts/00_asm/01_syntax.tex}
 \input{parts/00_asm/02_data-types.tex}
 \input{parts/00_asm/03_operations.tex}
+\input{parts/00_asm/04_control-flow.tex}
 
 
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