On Sunday 15 April 2007, Johannes Schindelin wrote:
> On Sun, 15 Apr 2007, Shawn O. Pearce wrote:
> > static int simple_length(const char *match)
> > {
> > - const char special[256] = {
> > - [0] = 1, ['?'] = 1,
> > - ['\\'] = 1, ['*'] = 1,
> > - ['['] = 1
> > - };
> > int len = -1;
> >
> > for (;;) {
> > unsigned char c = *match++;
> > len++;
> > - if (special[c])
> > + switch (c) {
> > + case 0: case '?':
> > + case '\\': case '*':
> > + case '[':
> > return len;
> > + }
> > }
> > }
>
> You are replacing a table-based check with a switch based, which might be
> substantially slower (depends on how often cmp_name() is called).
Or faster. When the table gives a cache miss and has to be
loaded from main memory, I am quite sure that 5 compares in a row are
faster than the cache miss.
Actually, with the switch, the compiler is free to implement it with a
table (and gcc usually does this, probably even using a substantially
smaller table). The table-based check in contrast looks
like some kind of micro-optimization which makes the code IMHO more
difficult to read, and which only would be justified with meassured
improvements.
Josef
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