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<H2><A NAME="SECTION00918000000000000000"></A><A NAME="4158"></A>
<BR>
8.1.8 Bit-shifting Operations.
</H2>

<P>
Bit shifting is one of the most frequently used operation in embedded
programming. SDCC tries to implement bit-shift operations in the most
efficient way possible, e.g.:
<BLOCKQUOTE>
<TT>unsigned char i;</TT>&nbsp;
<BR><TT>... </TT>&nbsp;
<BR><TT>i &gt;&gt;= 4; </TT>&nbsp;
<BR><TT>...</TT>

</BLOCKQUOTE>
generates the following code:
<BLOCKQUOTE>
<TT>mov&nbsp; a,_i </TT>&nbsp;
<BR><TT>swap a </TT>&nbsp;
<BR><TT>anl&nbsp; a,#0x0f </TT>&nbsp;
<BR><TT>mov&nbsp; _i,a</TT>

</BLOCKQUOTE>
In general SDCC will never setup a loop if the shift count is known.
Another example:
<BLOCKQUOTE>
<TT>unsigned int i; </TT>&nbsp;
<BR><TT>... </TT>&nbsp;
<BR><TT>i &gt;&gt;= 9; </TT>&nbsp;
<BR><TT>...</TT>

</BLOCKQUOTE>
will generate:
<BLOCKQUOTE>
<TT>mov&nbsp;&nbsp;a,(_i + 1) </TT>&nbsp;
<BR><TT>mov&nbsp;&nbsp;(_i + 1),#0x00 </TT>&nbsp;
<BR><TT>clr&nbsp;&nbsp;c </TT>&nbsp;
<BR><TT>rrc&nbsp;&nbsp;a </TT>&nbsp;
<BR><TT>mov&nbsp;&nbsp;_i,a</TT>

</BLOCKQUOTE>

<P>
<BR><HR>
<ADDRESS>

2011-03-20
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