Re: [PATCH] Speedup prefixcmp() common case

"Marco Costalba" [off-list ref] writes:

On Dec 29, 2007 8:32 PM, Junio C Hamano [off-list ref] wrote:

quoted

Why isn't it like this?

        if (!prefix[1])

well, what about if prefix == NULL ?

What about it?  Do not trim what's relevant when your quote,
please.

Your slow path does this:

 	return strncmp(str, prefix, strlen(prefix));
 }

So it will barf when prefix == NULL anyway due to strlen().  I
think passing NULL as prefix to prefixcmp() is a caller-error.

I think my version is also buggy.  Passing "" as prefix to
prefixcmp() is nonsense but is supported, and checking prefix[1]
without looking at prefix[0] reads past the end of the string.

So, in summary, I think the following is what we would want.

 static inline int prefixcmp(const char *str, const char *prefix)
 {
+	// shortcut common case of a single char prefix
+	if (prefix[0] && !prefix[1])
+		return *str - *prefix;
+
 	return strncmp(str, prefix, strlen(prefix));
 }