more editing of chapter 3

book.tex

@@ -747,7 +747,7 @@ following grammar.
 
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\chapter{Integers and Variables}
+\chapter{Compiling Integers and Variables}
 \label{ch:int-exp}
 
 This chapter concerns the challenge of compiling a subset of Racket,
@@ -906,7 +906,7 @@ called \emph{registers}, and instructions may load and store values
 into \emph{memory}.  Memory is a mapping of 64-bit addresses to 64-bit
 values. Figure~\ref{fig:x86-a} defines the syntax for the subset of
 the x86-64 assembly language needed for this chapter.  (We use the
-AT\&T syntax that is expected by the GNU assembler inside \key{gcc}.)
+AT\&T syntax expected by the GNU assembler inside \key{gcc}.)
 
 An immediate value is written using the notation \key{\$}$n$ where $n$
 is an integer. 
@@ -915,23 +915,20 @@ A register is written with a \key{\%} followed by the register name,
 such as \key{\%rax}.
 %
 An access to memory is specified using the syntax $n(\key{\%}r)$,
-which reads register $r$, obtaining address $a$, and then offsets the
-address by $n$ bytes (8 bits), producing the address $a + n$. The
-address is then used to either load or store to memory depending on
-whether it occurs as a source or destination argument of an
-instruction.
+which reads register $r$ and then offsets the address by $n$ bytes (8
+bits). The address is then used to either load or store to memory
+depending on whether it occurs as a source or destination argument of
+an instruction.
 
-An arithmetic instruction, such as $\key{addq}\,s\,d$, reads from the
+An arithmetic instruction, such as $\key{addq}\,s,\,d$, reads from the
 source $s$ and destination $d$, applies the arithmetic operation, then
-write the result in $d$. So the \key{addq} instruction computes $d
-\gets d + s$.
+write the result in $d$.
 %
 The move instruction, $\key{movq}\,s\,d$ reads from $s$ and stores the
 result in $d$. 
 %
 The $\key{callq}\,\mathit{label}$ instruction executes the procedure
-specified by the label, which we shall use to implement
-\key{read}. 
+specified by the label.
 
 \begin{figure}[tbp]
 \fbox{
@@ -980,11 +977,11 @@ that the operating system can call it. The label \key{\_main:}
 indicates the beginning of the \key{\_main} procedure which is where
 the operating system starting executing this program.  The instruction
 \lstinline{movq $10, %rax} puts $10$ into register \key{rax}. The
-  following instruction \lstinline{addq $32, %rax} adds $32$ to the
-    $10$ in \key{rax} and puts the result, $42$, back into
-    \key{rax}. The instruction \key{retq} finishes the \key{\_main}
-    function by returning the integer in the \key{rax} register to the
-    operating system.
+following instruction \lstinline{addq $32, %rax} adds $32$ to the
+$10$ in \key{rax} and puts the result, $42$, back into
+\key{rax}. The instruction \key{retq} finishes the \key{\_main}
+function by returning the integer in \key{rax} to the
+operating system.
 
 
 \begin{wrapfigure}{r}{2.25in}