Hi Compiler Experts,
I am using flex to generate a scanner. It creates a yy_get_next_buffer()
function in lex.yy.cc among other things.
I want to discuss a particular performance issue and how I tried to fix it. I
am wondering why it is not part of the default scanner generated by flex
because I think the developers must have seen this too.
When I run a particular test-case, I see a lot of time being taken by this
function (yy_get_next_buffer). On running tools like "quantify" to measure
performance, I found that these particular lines in yy_get_next_buffer() are
taking a lot of time.
/* First move last chars to start of buffer. */
number_to_move = (int) ((yy_c_buf_p) - (yytext_ptr)) - 1;
for ( i = 0; i < number_to_move; ++i )
*(dest++) = *(source++);
When I change this to the following, I get a huge improvement in performance.
/* First move last chars to start of buffer. */
number_to_move = (int) ((yy_c_buf_p) - (yytext_ptr)) - 1;
memcpy(dest,source,number_to_move);
-regards
Gautam
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